the garden atrium apartment
TRANSCRIPT
7
APPROPRIATE HIGH DENSITY URBAN HOUSING PROTOTYPE
FOR THE LAGOS MEGACITY: THE GARDEN ATRIUM
APARTMENT Olumide Olusanya
University of Lagos, Department of Architecture, Lagos, Nigeria
Phone no.: +234-802-3065-560 E-mail: [email protected]
Keywords: environmental comfort in tropical climate, urban housing, natural light and
ventilation, public and private space, skywalk.
Abstract
Lagos is the commercial capital of Nigeria with an estimated population of seventeen million,
the largest in Africa. It is generally regarded as the fastest growing city in the world and
expected to rank amongst the three largest megacities by year 2015 at its present rate of
growth.
Two problems compound one another to create a disastrous housing situation: a monumental
shortfall in the requirement for housing and the general proliferation of sub-standard
inadequate housing forms. The most common form of urban housing in Lagos is the double
banked apartment block with rooms or flats on two sides opening to a common corridor
leading to a stairwell. The corridor is generally narrow with poor lighting and ventilation.
Cross ventilation is difficult to achieve within the flat because the door to the corridor is
always locked for reason of security and windows do not open to it for reason of privacy.
One innovation that has been found to satisfy the requirements for environmental comfort in
an urban and tropical climate is an upgrade that adds value to a familiar form. The double
loaded corridor is expanded into an atrium; the conventional 1.2m corridor is converted into
a skywalk suspended in the atrium, opening all the way to clearstory windows in the roof to
catch both breeze and natural light. Light wells on both sides of the skywalk transfer light
and breeze all the way to the ground level as well as provide a buffer (for privacy) between
the apartment and the walkway. The system of skywalks organizes the circulation arteries
into a gradation of public, semi-public, semi private and private spaces. This allows the
atrium to double as a social, as well as circulation space. The spaces below the light wells
are landscaped to create an indoor garden on the ground floor with plants growing through
the wells to the upper reaches of the atrium.
This paper presents the actualization of this concept in a small scale prototype; a hostel
apartment block, and design of the scaled up prototype being adopted by the Lagos State
Government for a large scale housing program.
INTRODUCTION Traditionally the 3 basic ways of organizing functions and circulation spaces in building
layouts are:
The single banked corridor (fig.1)
The double banked corridor (fig.2)
The courtyard corridor
8
Spatial modules of rooms, classrooms, offices and
apartments organized along or around linear circulation
spaces are utilized in various building typologies, to
include commercial, institutional and residential.
The single banked corridor, offers the most efficient
utilization of natural lighting and cross ventilation. The
disadvantages are that windows opening directly onto
circulation spaces compromise privacy; also the
arrangement does not make for efficient use of land.
The double banked corridor on the other hand, is
extremely efficient in terms of cost and land utilization,
which makes it the most prevalent of all architectural
layouts for a wide range of use.
Its main disadvantage is that in the tropical climate, the
corridors can be dark and stuffy while the rooms that
open onto it and are hard to ventilate without loss of
privacy.
The courtyard corridor layout has the advantage of
some ventilation and its land use is better than the
single banked corridor. However its land use is not
efficient in prime urban land and privacy is
compromised where windows open to the corridors in
a residential layout.
The garden atrium concept (fig.3 & 4) is an attempt to resolve and harmonise the issues of
efficient land use, optimal light, cross ventilation and privacy in the tropical climate.
The Garden Atrium
The concept combines the
advantages of the double
banked and the courtyard
corridors by expanding the
circulation space into an
atrium opening all the way
to the roof. The dimension
of the circulation corridor
is retained and suspended
in the atrium thereby
providing the light wells
on either side .The interior spatial modules can then be opened to the light wells for natural
light and ventilation without loss of privacy. The key feature of the concept is a landscaped
atrium with plants shooting through the light wells towards the roof. This makes it an
embodiment of green and sustainable architecture.
The Institute Of Venture Design
The Institute of Venture Design in Abeokuta (60km to the North of Lagos) is a centre for
research and development work. It consists of a hostel and an academic block. The hostel
block is designed to provide continuous interaction amongst the research fellows
The garden atrium concept is here adapted to a slopping site to provide hostel rooms, dining
hall, and a variety of lounges and other services.
1 1
2
3
a
b c
a-private b-semi-private c- semi-public
d- light/air well
d .
4
9
Institute Of Venture Design Prof. Olumide Olusanya: architect
A thermal comfort field study of the hostel block was conducted with the aim to investigate
the comfort temperature, occupants’ behaviour and the breaking of barriers to comfort. In the
dry season, the opening of windows scored almost 98% for always and most often and scored
93% in the rainy season; it is thus the most favoured adaptive control out of six; followed by
cold drink, go to the atrium, take a bath, change cloth and switch on A/C, in that order. The
high preferences for the opening of windows signify that wind or air movement inside the
building is highly favourable and essential to enhance occupants thermal comfort satisfaction.
(Adebamowo and Olusanya 2012)
5
6
10
The steel
handrails double
as trussed bridges
suspended into the
atrium as
circulation
arteries. The floor
of the suspended
bridge is 75mm
r.c. slab for a total
of 5.6m3 of
concrete. A
conventional r.c.
beam and slab
construction for
the circulation
artery would have
required 20.57m3
of concrete. Since
the hand railing is
an imperative in
either mode of
construction, the
suspended bridge
represents about
75% reduction in
material. This
would translate
into significant
cost and time
savings especially
on large scales for
mass housing
production.
7
11
Mass Housing Prototype for the Lagos Mega City:
Garden Atrium Maisonette Apartments
The garden atrium concept utilized for the organization of hostel rooms at the Institute of
Venture Design, is proposed for the organization of low rise maisonette apartments for Lagos
State Government’s mass housing scheme. Its main advantage for mass housing production is
the modularized layout which lends itself to standardized prefabricated components (systems
building) for rapid site assembly. A system building tailored to the level of industrial
development in Nigeria, developed by Professor Olusanya, and successfully utilized in some
previous projects are proposed for the wall and floor systems (fig.11&12). The use of
prefabricated trusses for the suspended circulation would result in huge cost and time savings
in a multi-storey construction.
Proposed Garden Atrium Maisonette Apartments Prototype for Lagos State Government Mass Housing Scheme.
Prof. Olumide Olusanya: architect
8
9
12
The system of skywalks on several levels of the multi-story block organizes the circulation
arteries into an evolving hierarchy of defensible space from public, semi-public, semi private
to private. (Fig. 3 & 9)
According to Oscar Newman (1972), defensible space design returns to the productive use of
residents, the public areas beyond the doors of individual apartments: the hallways, lobbies,
grounds and surrounding streets, areas which are [normally] beyond the control of
inhabitants. Certain elements of physical designs are used for the creation of secure
environment; i.e. the territorial definition of space in developments reflecting the areas of
influence of the inhabitants. This works by sub dividing the residential environment into
zones towards which adjacent residents easily adopt proprietary attitude.
Conclusion
The garden atrium approach to natural lighting and ventilation combined with optimal land
use is designed to minimize waste and to achieve considerable reduction in energy
consumption, both in the capital and running cost of housing. This appropriate technology
approach, in a developing economy, provides a useful tool in addressing the problem of
housing inadequacy in relation to environmental comfort in a tropical climate.
REFERENCES
[1] Mike Adebamowo and Olumide Olusanya (2012). Energy savings in housing through
enlightened occupant behaviour and by breaking barriers to comfort: A Case Study of a
Hostel Design in Nigeria. Low Energy Architecture Research, vol7 no1, p.101.
[2] Oscar Newman (1972). Defensible space: HUD office of the policy development and
research. Washington D.C. p. 8-9.
[3] Olumide Olusanya (2007). World class housing and sustainable industrial production:
strategies and tactics for a developing economy: private sector driven housing delivery:
issues challenges and prospects A book of readings .Ed: T. Nubi ‘et al department of estate
management, university of Lagos. p.237-247
10
13
Extent of commercial use of stabilised earth construction alleviating urban
housing crisis in Africa
Dr. Mohammad Sharif Zami & Dr. Mohammad Babsail
Department of Architecture
College of Environmental Design
King Fahd University of Petroleum & Minerals (KFUPM)
KFUPM Box: 1802, Dhahran 31261
Saudi Arabia
Email: [email protected] and [email protected]
Key words: Earth construction, extensive, commercial, urban, housing
ABSTRACT
Rural urban migration is a common phenomenon in most of the African countries which
leads the shortage of affordable housing in the urban areas. Several studies have shown that
contemporary stabilised earth construction has the potentials to alleviate the urban housing
crisis in African countries. The aim of this paper is to critically review and argues the extent
of commercial usage of stabilised earth construction to address urban housing crisis in
Africa as this indicates success of this technology. A Delphi method is adopted in this paper
to investigate and ascertain from the construction professionals the extent of commercial
usage of stabilised earth construction alleviating urban housing crisis in Africa.
INTRODUCTION
There is an urban housing crisis in most of the developing countries and this is largely
attributed by the rapid urbanisation (Dwyer et al, 1981, 33). According to Kamete (2006), the
housing crisis is often sold and pushed onto the agenda in pre-dominantly quantitative terms
and the mismatch between supply and demand is perhaps the scariest indicator used by
proponents of increased housing delivery. The majority of the urban local authorities and
central governments did and do not have a tradition of providing shelter to a large permanent
population; there has been a lag of supply to demand of urban housing (Zami and Lee, 2007).
According to UN Habitat (1996), housing shortage in African cities ranges from 33% to 90%.
To meet housing needs, many people have resorted to renting backyard shacks and squatting
on illegal land. The unprecedented boom in the construction industry since independence
resulted in the high demand of building materials that superseded the production capacity of
the manufacturing sector in most of the African countries (Zami and Lee, 2008). According
to the South African census report of 1996, 1,049,686 households lived in informal
dwellings. People reside in squatter settlements, where there are no provisions for social
services and utilities. UN Habitat (1996) also estimates that approximately 60% of the
African population resides in shantytowns, slums and uncontrolled settlements.
The aim of this paper is to find out the extent of commercial usage of stabilised earth as an
alternative material to housing in such a way, that if compared to established materials, it
should prove to be an ideal alternative. Furthermore, to achieve the aim, the authors critically
review relevant literature and adopt the Delphi technique to analyse and validate the
arguments of this paper. The following section reviews the current state of art of the
successful cases of contemporary stabilised earth construction to establish a base for the
Delphi technique study as to compare the literature against construction professional
perspectives.
14
CONTEMPORARY EARTH CONSTRUCTION METHODS AND COST
COMPARISON
Historically, earth was used as a construction material all over the world. Among the most
widely known and practical construction methods are rammed earth in formwork, brick
moulded in raw earth and baked by the sun or ‘adobe’ and compressed earth blocks, which
are produced in presses (Houben & Guillaud, 1989). At present, stabilisation of earth is a
common modern construction method; it modifies the properties and characteristics of soil,
but does not necessarily improve quality.
Adobe Block, Compressed Stabilised Earth Block (CSEB) and Rammed Earth (RE) are the
most common earth construction methods experimented in most African countries (Zami,
2010). Considering the local situation and the drawbacks of earth construction, the stabilised
form (RE/CSEB) of earth construction is most suitable to address the low cost housing crisis
in most of the countries in Africa, because the drawbacks that are derived and discussed in
the literature are from the experience of un-stabilised earth construction. The drawbacks
associated with un-stabilised earth construction can be overcome by suitable improvements in
design and technology, such as soil stabilisation, appropriate design, and improvement in
structural techniques. According to Walker et al. (2005) rammed earth is formed by
compacting moist subsoil inside temporary formwork. Stabilised Rammed Earth is an
alternative form of wall construction that uses the rammed earth technique, but generally
includes cement (although other forms of stabilisers such as gypsum, lime and bitumen can
be applied), primarily as an additive to change the material’s physical characteristics (Walker
et al. 2005). Correct proportions of sand, clay and water are mixed together and poured into
the formwork in layers of 100 to 150mm deep, and compacted by ramming to the sufficient
wall strength after which the framework is moved to another section of the wall, either
horizontally or vertically, repeating the same process until the wall is finished. Figure 1
shows the manufacturing process of RE production.
Figure 1
Production process of in situ stabilised rammed earth. Source: Zami and Lee (2010)
Compressed stabilised earth bricks or blocks are becoming popular in various parts of the
world especially with the growing need for sustainable construction, and soil is the main raw
material used in CSEB manufacturing (Jayasinghe, 2007). Some of the process stages in the
production and construction of compressed stabilised earth blocks are similar to RE. Figure 2
shows the manufacturing process of CSEB production.
Drying Excavation
of soil Screening
of soil Pulverisation Dry mixing
Add
Stabiliser
Add Water
Ramming Reaction
Loading the
soil into
formwork Wet
mixing
Drying
15
Figure 2
Production process of stabilised compressed earth block. Source: Zami and Lee (2010)
Considering the widespread adoption of contemporary stabilised earth construction to address
the urban housing crisis in Africa, the economic benefit would be the primary reason to adopt
this technology (Zami, 2010). According to Hadjri et al (2007) in Zambia, housing
construction using conventional materials (brick and concrete) is too expensive for the
majority in urban areas where transport amounts to about 40% of the total material cost.
Gooding and Thomas (1995) carried out an economic analysis of building materials
competing for the urban and peri-urban markets, which shows that cement stabilised earth
block is cheaper compared to the conventional building material in several developing
countries. Maini (2005) further states that in Auroville (India), a finished cubic metre of
CSEB wall is generally 48.4% cheaper than wire cut bricks, and 23.6% cheaper than country
fired bricks. However, Figure 3 shows the reported cost reduction of some case studies using
earth construction in some African countries.
Figure 3
Reported cost reduction of some case studies using earth construction in Africa. Source: Authors, 2012.
CASES OF CONTEMPORARY EARTH CONSTRUCTION PROJECTS IN AFRICA
From thorough investigation of the literature review it seems to appear that majority of
experimented CSEB (Compressed Stabilised Earth Blocks) and RE (Rammed Earth) projects
in Africa are successful. This section is going to bring in some success cases of contemporary
earth construction in Africa. Existing urban structures of earth in Zimbabwe can be seen
mainly in the houses of the Crainbone suburb of Harare and in Bulawayo’s Sourcetown
suburb. Initially Zimbabwean professionals did not recognise the use of earth for construction
of ‘descent’ shelter for the urban environment (Zami and Lee, 2007). The recognition of
Drying Excavation
of soil
Screening
the soil Pulverisation Dry mixing
Add Stabiliser
Add Water
Construction Curing Block moulding Drying
16
stabilised earth construction was expedited by the adoption of Zimbabwe Standard Code of
Practice for RE structures which was first published in 1996 (Kannemeyer, 2006) and
included in the Zimbabwe Model Building Bylaws in 2004.
The performance of experimental RE and CSEB construction in Zimbabwe is a great success
to date (Mubaiwa, 2002; Kannemeyer, 2006). One of the first stabilised earth projects was the
British government’s Overseas Development Administration (ODA) funded, the DfID School
block at the SIRDC (the Scientific and Industrial Research and Development Centre),
Hatcliffe, Harare, Zimbabwe. The building was inexpensive, and showed that wide span roofs
are possible with the technology, important for classrooms and clinics. The construction cost
of this block was 60% cheaper than the traditional concrete brick and blocks construction
(Zami, 2010). Besides, a number of RE projects in the country was carried out amongst some
of them were a private house in Bonda, Manicaland in 1997, Office and housing (Figure 4) in
Chimanda on the North East border with Mozambique. SIRDC built a RE teacher’s house
(Figure 5) at Rukanda Secondary School in Mutoko. Costs incurred in building the two
roomed Rukanda teacher’s house shows that construction using RE and roofing with MCR
(micro-concrete roofing) tiles resulted in a low cost of 18 million Zimbabwe dollars
compared to $45 million when using conventional technologies. The Chitungwiza House is
one of the few known buildings made of CSEB. This pilot project by the Intermediate
Technology Group (ITG) was implemented with the participation of the Chitungwiza
municipality in 1993 as a low income house. The aim of this project was to evaluate the
response of the people towards earth structure and the performance of low tech and
sustainable materials used in the construction of low cost housing. The use of local labour
and the absence of imported materials sent a message to the local communities that the
solution of affordable sustainable and low cost housing is possible. Until now this structure
stands as a success to all participants working in the housing industry in Zimbabwe.
Figure 4 Figure 5
Chimanda office under construction. House built by SIRDC at Rukanda School.
Source: Ram Cast CIC website, 2008. Source: The Herald, ZITF Supplement.
Compressed stabilised earth blocks were successfully used for low-income housing in Sudan
(Adam and Agib, 2001 cited in Hadjri et al. 2007). According to Adam and Agib (2001), the
cost of producing compressed stabilised earth blocks will vary a great deal from country to
country and even from one area to another within the same country. Unit production costs
will differ in relation to local conditions. Adam and Agib (2001) also noted that block making
can be carried out on a ‘self-help’ basis, where labour costs are eliminated and soil is often
available at no cost. The Al Haj Yousif experimental prototype school was constructed from
compressed stabilised earth blocks, and was found to be very cost effective by Sudanese
17
standards. The total savings made, in cost per square metre, were approximately 40%
compared to conventional brick and block construction. Similar findings were also reported
in Kenya where the average unit cost of compressed stabilised earth blocks is approximately
20% to 70% that of concrete blocks, depending on the method of production followed (Adam
and Agib, 2001).
Similar to the Al Haj Yousif School, Gando Primary School in Burkina Faso is also a
success story of CSEB. This school is the result of one man’s (Architect Diébédo Francis
Kéré) mission to improve conditions in his village. Not only did he design the school and
raise the funds to build it; he also secured government support to train people in building with
local materials, and drew on the strong tradition of community solidarity to engage all of the
villagers in the construction of this school for their children. Construction of the school began
in October 2000, carried out largely by the village’s men, women and children. After the
school was completed in July 2001, construction of buildings for resident teachers began
along similar principles. To achieve sustainability, the project was based on the principles of
designing for climatic comfort with low-cost construction, making the most of local materials
and the potential of the local community (Website: Aga Khan Award for Architecture).
Mumemo is about a training course carried out in Mumemo (Maputo, Mozambique) on earth
construction by two Portuguese architects, Miguel Mendes and Teresa Beirao, during May
and August 2006. The project was created for the inhabitants of a new village, created as a
resettlement for the victims of the massive floods in the year 2000. The course gave students
a wide and solid knowledge about earthen construction and three main techniques (rammed
earth, adobe, compressed earth blocs) as well as provided them with the ability to direct
similar courses in other communities. During the course, a small 50m2 house was built
shown in (Website: Mumemo, 2009).
The aim of these contemporary earth construction projects was to evaluate the response of the
people towards contemporary earth structure and the performance of low tech and sustainable
materials used in the construction of urban housing. The use of local labour and the absence
of imported materials sent a message to the local communities that the solution of affordable
sustainable and urban housing is possible. Until now these structures stand as a success to all
working in the housing industry in Africa. Surprisingly stabilized earth construction
technology has not been adopted to address the urban housing crisis in Africa despite the fact
that the experimental projects are successful. This section has reviewed that the experimental
use of stabilised earth as an alternative building material is worthwhile in the light of
successful African cases of earth construction. But the use of stabilised earth construction in
urban housing is not yet extensive to date. Therefore, it is important to investigate the extent
of its commercial use.
RESEARCH METHODOLOGY
After a critical review of the existing literatures, it appears that there is a lack of structured
research, to date, carried out to investigate the extent of commercial use of contemporary
stabilised earth construction alleviating urban housing crisis in Africa. The critical review of
the successful cases in the literature intended to permit the researcher to recognise and
identify the existing commercial usage of stabilised earth construction in Africa. The extent
of usage of stabilised earth construction is found in the literature. Therefore, the research
technique adopted in this paper is interviews (Delphi technique) which effectively collect
information from construction professionals all over the world.
18
The Delphi technique can be applied to problems that do not lend themselves to precise
analytical techniques but rather could benefit from the subjective judgments of individuals on
a collective basis (Adler and Ziglio, 1996) and to focus their collective human intelligence on
the problem at hand (Linstone and Turloff, 1975). Therefore, for this research, the Delphi
technique is chosen as a suitable research technique because the results will offer an informed
look at the current and potential status of the use of stabilised earth construction in general.
Based on the nature, attitudes and beliefs of a carefully selected group of expert respondents,
the extent of use of stabilised earth construction are captured.
The Delphi technique adopted for this research consists of two rounds, whereby the second
round was constructed from question and feedback acquired from the previous question. The
aim of the question in the first round was to elicit the extent of commercial use of stabilised
earth alleviating urban housing in Africa. The second round of the Delphi technique
summarised the expert’s comments and were presented to the experts for reconsideration and
validation. A list of thirty-four (34) participants (experts) was contacted from both the private
and public sector that would appear to have the required knowledge and/or experience of the
subject. Therefore, thirty four letters were sent out inviting them to take part in this Delphi
technique. A total of fourteen (14) individuals responded and agreed to participate, equating
to a 41% response rate. Out of the fourteen (14) individuals, seven (07) were academician
researchers, one (01) was a practitioner, and six (06) were practitioner researchers. During the
second round of administering the Delphi technique, three (03) academician researchers and
one (01) practitioner experts did not respond, which made a total of ten (10) participants.
Only two rounds of the study were needed for the participants to reach a consensus. Experts
remain anonymous in this study and they are called by the English letters A-N.
ANALYSIS AND DISCUSSION OF THE FINDINGS OF THE DELPHI FIRST
ROUND
All experts were asked what is the extent and commercial use of stabilised earth construction
in urban low cost housing in Africa? Out of the fourteen experts surveyed, only thirteen
responded to the question. Three (21%) out of the fourteen experts agreed that stabilised earth
construction is used extensively and commercially in urban low cost housing, whereas the
remaining ten (72%) respondents disagreed.
According to Expert ‘F’, generally architects and engineers are not convinced of the
usefulness of earth construction. Expert ‘H’ stated, “I would not say there is extensive
application of stabilised earth for urban housing, but there is moderate use. The new building
technologies are difficult to disseminate. Because of environmental and economic benefits
these technologies are being slowly and steadily picked-up by the public”. It is important to
note that, stabilised earth construction is not used extensively and commercially even though
it is environmentally and economically beneficial in the construction of urban low cost
housing. Awareness of its benefit and architecture-aesthetic values is growing in select Indian
cities, such as Bangalore. In support of the majority of expert opinion, Expert ‘E’ stated,
“Where there is a tradition of building in earth, as in parts of Africa, North, Central and
South America, Central and Western Asia, parts of India and China, adobe, pise, and
stabilised earth may still be used extensively and commercially”. Therefore, the viability and
possibility of stabilised earth construction in urban low cost housing is well supported by the
experts. Although Expert ‘C’ and ‘H’ responded ‘Yes’ to this question and confirmed that
there are many projects using stabilised earth in Australia and India, Expert ‘K’ stated that,
“though many commercial and residential projects in Australia are done with earth
construction it is still very much a ‘fringe’ industry, even in countries such as Australia
19
(10,000 + modern buildings) and India (80,000+ modern buildings)”. This statement provides
an argument that though there are more projects being done with stabilised earth construction
in Australia and India compared to the other countries around the globe, the question needs to
be asked: is this number of projects enough to conclude that stabilised earth construction is
used extensively and commercially in Australia and India?
It is also noted that, in Peru, stabilised earth construction methods are used extensively by
people with low economical resources but they are not used in a commercial way and
moreover, they are not used extensively in the UK at present. Therefore, according to most of
the expert’s opinions stabilised earth construction is not yet used extensively and
commercially in the construction of urban low cost housing in all over the world.
ANALYSIS AND DISCUSSION FROM THE DELPHI SECOND ROUND
The second round of the Delphi technique brought about a more detailed explanation on the
extent and commercial use of stabilised earth construction in urban low cost housing.
According to Expert ‘M’, there are 5,000 urban houses built with CSEB in Sri Lanka, which
is a clear indication that people are appreciating and slowly starting to use contemporary
earth construction. It is as also shown by Expert ‘M’ that the building regulations in most
major urban settlements, even in countries where there is a well-established tradition of
building in earth, discriminate against most earth based building materials and techniques.
According to Expert ‘N’, contemporary stabilised earth construction is not yet used
extensively because of the lack of training for the professionals; especially the fact that the
universities do not teach earthen architecture which results in limited knowledge amongst the
building industry professionals.
CONCLUSIONS
In response to the Delphi question, the majority of experts agreed that the extent of use of
stabilised earth construction is limited and not used commercially all over the world. Besides,
it is evident from the existing literature that experimented stabilised earth construction in
urban housing is environmentally sustainable compare to the conventional (fired brick,
concrete, etc.) building materials. Promotion and implementation of earth as an alternative
low cost urban house construction material is worthwhile and significantly helpful in
achieving environmental sustainability. Earth is affordable and available and would be
appropriate in the case of affordable urban house construction in in many African countries.
Therefore, the promotion and implementation of stabilised earth as an alternative building
material is worthwhile in the light of successful African cases of earth construction. It is
possible to use un-stabilised raw earth as rammed earth or compressed earth blocks; but the
stabilised form is more suitable for the African situation in terms of by-laws and housing
standards stipulated by the municipalities. The flexibility and simplicity in technology
incorporated in earth building affords adaptability and easy transfer of knowledge between
different stakeholders in the building industry. Individuals and community as a whole can
easily participate in building their own homes in affordable ways.
ACKNOWLEDGEMENTS The authors are grateful to King Fahd University of Petroleum and Minerals (KFUPM),
Dhahran, Saudi Arabia for their support to write and present this paper to the 5th
International Conference on Appropriate Technology November 20-24, 2012, Pretoria, South
Africa.
20
REFERENCES
[1] Adam, E. A. and Agib, A. R. A. (2001). Compressed Stabilised Earth Block
Manufacture in Sudan. Printed by Graphoprint for the United Nations Educational,
Scientific and Cultural Organization. France, Paris, UNESCO.
[2] Adler, M. and Ziglio. E. (1996). Gazing into the oracle: The Delphi Method and its
application to social policy and public health. London: Jessica Kingsley Publishers.
[3] Aga Khan Award for Architecture Website, (2008).
http://www.akdn.org/akaa_award9_awards_detail2.asp
[4] Dwyer, D. J. (1981). People and Housing in Third World Cities, perspectives on the
problem of spontaneous settlements. Longman Group Limited, London and New York.
[5] Hadjri, K., Osmani, M., Baiche, B. And Chifunda, C. (2007). Attitude towards earth
building for Zambian housing provision. Proceedings of the ICE institution of civil
engineers, engineering sustainability 160, issue ES3.
[6] Houben, H. and Guillaud, H. (1989). Earth construction. Intermediate Technology
publications 1994, London.
[7] Jayashinghe, C. (2007). Characteristics of different masonry units manufactured with
stabilized earth. International Symposium on Earthen Structures, Indian Institute of Science,
Bangalore, 22-24 August. Interline Publishing, India.
[8] Kamete, A. Y. (2006). Revisiting the urban housing crisis in Zimbabwe: some
forgotten dimensions? Habitat International, 30, 981-995. Elsevier Ltd.
[9] Kannemeyer, H. S. (2006). Towards sustainable low-cost housing through green
architecture: a look at rammed earth housing in Zimbabwe. Undergraduate Dissertation,
Department of Architecture, National University of Science and Technology, Bulawayo,
Zimbabwe.
[10] Linstone, H. and Turoff, M. (1975). “Introduction” in the Delphi Method: Techniques
and Applications Linstone and Turoff (Eds) Addison-Wesley Publishing Company, London.
[11] Maini, S. (2005). Earthen architecture for sustainable habitat and compressed stabilised
earth block technology. Progrmmae of the city on heritage lecture on clay architecture and
building techniques by compressed earth, High Commission of Ryadh City Development.
The Auroville Earth Institute, Auroville Building Centre – INDIA.
[12] Mubaiwa, A. (2002). Earth as an alternative building material for affordable and
comfortable housing in Zimbabwe: Undergraduate Dissertation. Department of Architecture,
National University of Science and Technology, Bulawayo, Zimbabwe.
[13] Mumemo Website, (2009). Accessed 12.12.2010.
http://www.eartharchitecture.org/index.php?/archives/1047-MUMEMO.html
[14] UN HABITAT (1996). Participation in Shelter Strategies at Community Level in
Urban Informal Settlements. UN Habitat.
[15] Walker, P. Keable, R. Martin, J. and Maniatidis, V. (2005). Rammed earth: Design and
Construction Guidelines. BRE Bookshop, Zimbabwe.
[16] Zami, M. S. and Lee, A. (2007). Earth as an alternative building material for
sustainable low cost housing in Zimbabwe. The 7th International Postgraduate Research
Conference. March 28 – 29, 2007, The Lowry, Salford Quays, Salford, Greater Manchester,
United Kingdom.
[17] Zami, M. S. and Lee, A. (2008). Forgotten dimensions of low cost housing crisis in
Zimbabwe. The 8th International Postgraduate Research Conference. June 26 – 27, 2008, the
Czech Technical University of Prague (CVUT), Czech Republic.
[18] Zami, M.S. (2010). Understanding the factors that influence the adoption of stabilised
earth by construction professionals to address the Zimbabwe urban low cost housing crisis.
PhD thesis submitted to University of Salford, United Kingdom.
21
SUSTAINABLE CONCRETE TECHNOLOGIES: A CASE STUDY OF
INSUDEK-MOKETE RIBBED SLABS AND WAFFLE-RAFT SYSTEMS
Usiri Paul1 and Kuchena Jabulani Charles
2,
1Ae-xergy (Pty) Ltd, Principal Engineer/Director
The Prism Office Park, Building 1, Fourways, Johannesburg South Africa
Phone: 0027 11 367 0698; Fax: 0027 86 668 5365; Cell: 0027 72 822 6043
Mail: [email protected]
2University of Johannesburg – Civil Engineering Department, Senior Lecturer
PO Box 395, Pretoria 001, South Africa
Phone: 0027 12 841 3830; Fax: 0027 12 841 3539; Cell: 0027 76 852 7127
Mail: [email protected]; [email protected]
Key words: Advanced Construction Technologies, Ribbed Suspended Slabs, Waffle-Raft
Foundation Slabs, Sustainable, Green Building
Abstract
The concrete-and-cement industry plays an integral part in the construction of the
contemporary built-environment; infrastructure and building structures inclusive. However,
cement production is not only a source of combustion-related CO2 emissions, but globally is
one of the largest sources of industrial beneficiation-related emissions, through limestone
calcining. Ribbed-slab and raft-foundation systems are an innovative method of constructing
slabs utilizing temporary or permanent voiding formwork. Formers are arranged in a grid
pattern, to produce lighter and stiffer slabs, capable of achieving up-to 60% less concrete
usage and redundancy. The systems offer a more economical method of carrying light to
moderate loads on long spans, than with conventional solid slabs. Inadvertently, this has
opened up new possibilities for faster construction of building structures. New leaner,
stronger, energy efficient buildings can be constructed incorporating ribbed slab and raft
foundation systems.
This paper broadly explores, on a more disaggregated level, the development and adoption
rib-and-block and waffle-slab systems in South Africa. The paper presents a case study, on
the authors’ research and experiences with a proprietary Insudek-Mokete™ ribbed slab and
waffle-raft system. The paper also explores the industrial paradigm shift towards advanced-
sustainable ‘green building’ construction technology in South Africa and the SADC region.
INTRODUCTION
According to the Green Building Council of South Africa (2012), a “green building” is a
building which is energy efficient, resource efficient and environmentally responsible - it
incorporates design, construction and operational practices that significantly reduce or
eliminate the negative impact of development on the environment and occupants [5]. The
zeitgeist shift is to ensure that all buildings are built and operated in an environmentally
sustainable way so that humankind works and lives in healthy, effective and productive
environments. To this intent the construction materials and building systems we adopt have a
bearing on sustainability of the built environment.
1 Principal Engineer [email protected]
2 Senior Lecturer, [email protected]
22
Reinforced-concrete is a composite construction material, in which, concrete is designed for
its high-compressive strength characteristics and steel for its high-tension capacity. The
concrete and cement industry plays a vital part in the construction of the contemporary built-
environment; infrastructure and building structures inclusive. However, cement production is
not only a source of combustion-related CO2 emissions, but globally is one of the largest
sources of industrial beneficiation-related emissions, through the limestone calcining process.
Ribbed-slab and raft-foundation systems are an innovative method of constructing slabs
utilizing temporary or permanent voiding formwork. Formers are arranged in a grid pattern,
to produce lighter and stiffer slabs, capable of achieving up-to 60% less concrete usage. The
systems, offers a more economical method of carrying light to moderate loads on long spans,
than with conventional solid slabs. This is mainly because a considerable amount of concrete
in solid slabs, within the tension zone is redundant, as steel-reinforcement provides the
tension capacity.
Inadvertently, reducing this concrete redundancy has opened up new possibilities for faster
construction of building structures. New leaner, stronger, energy efficient buildings can be
constructed incorporating ribbed slab and raft foundation systems. Based on the authors’
local historical study, modern concrete pre-stress rib-block precast suspended flooring
systems have a proven track record of over 40 years in South Africa, This highly successful,
innovative design approach has proven versatility for irregular shapes and down lighters. The
hollow blocks offer excellent structural integrity, improved sound and heat insulation, and
allows for a high quality plastered finish. Substantial cost savings over conventional / in situ
slabs and speed of erection have made rib-block slabs a more attractive product for modern
building techniques. Rib-block slabs have been used on commercial and industrial projects,
as well as schools, town houses clusters and domestic homes.
OBJECTIVES According to Reddy-Venkatarama B. V. (2004), building materials and technologies, and
building practices have evolved through ages. Housing and building conditions reflect the
living standards of a society. Energy consumed in the manufacturing processes – energy
intensity; Problems of long distance transportation; Natural resources and raw materials
consumed; Recycling and safe disposal; Impact on environment, and Long-
term sustainability. Thus the issues related to energy expenditure, recycling, biodegradable,
environmental sustainability with respect to future demand needs to be addressed during the
manufacture and use of any new building material [13].
This objective of this paper is to broadly explore, on a more disaggregated level, the
development and adoption rib-and-block and waffle-slab systems in South Africa. The paper
presents a case study, on the authors’ research and experiences with a proprietary Insudek-
Mokete™ ribbed slab and waffle-raft system. The paper also explores the industrial paradigm
shift towards advanced-sustainable ‘green building’ construction technology in South Africa
and the SADC region. The investigation of the construction of rib-and-block and waffle-slab
systems is aimed:-
To promote and take advantage, in a sustainable and ecologically acceptable way, the
local resources for the production of alternative concrete construction materials;
alternative building construction technologies in South Africa and the SADC region.
To promote the production of local construction materials and alternative constructive
systems that are popularized and disseminated within Communities, Educational
Institutions and in the Professional Training Centres;
23
To contribute to the creation of regulations of alternative constructive systems and
uniformity of the method and quality of the local production materials.
JUSTIFICATION
Ribbed and waffle slabs provide a lighter and stiffer slab than an equivalent flat-solid slab,
reducing the extent of foundations. They provide a very good form where slab vibration is an
issue, such as laboratories and hospitals. Ribbed slabs are made up of wide band beams
running between columns with equal depth narrow ribs spanning the orthogonal direction. A
thick structural-top slab completes the system. Waffle slabs tend to be deeper than the
equivalent ribbed slab. Waffle slabs have a thin topping slab and narrow ribs spanning in both
directions between column heads or band beams; see different the types, Figure 1.
Insert 1: Prestressed Rib and Block Slab
Insert 2: Prestressed Rib and Block Slab
Insert 3: Steel Channel Rib and Polystrene Block
Slab
Insert 4 :Steel Channel Rib and Polystrene Block
Slab
24
Insert 5: Polystrene Block Raft Slab
Insert 6: Polystrene Block Raft Slab Concreting
Figure 1: Different proprietary rib-block and raft foundation systems.
From figure 1, it can be observed that rib-block systems, use less concrete and allow modular
installation as an advanced construction technology (ACTs). They have adapted modular
construction techniques from the process industry, which is tailored to large production
plants. The systems combine the advantages of factory offsite construction with the benefits
of modular construction. ACTs mimic the ordinary procedures of process plant construction
yet provide the advantages of traditional kit-units. Modules are assembled from
subcomponents built in specialty shops. The components are then moved to the assembly
floor/project where the concrete-module is constructed at the structural floor level [3]. METHODOLOGY
For the accomplishment of this work the following methodology was used:
A desk-top study has been undertaken to evaluate similar proprietary systems
currently in South African and the SADC region in general.
Research was also conducted on international experiences and structural concrete
design codes for rib-waffle slab systems and their construction applications.
Suitable representative locations for construction materials research were identified
and selected from the construction technology in South Africa and the SADC region
Research visits were carried out to selected areas (Field study) where Insudek-
Mokete™ ribbed slab projects have been constructed, in countries (South Africa,
Botswana, Lesotho, Swaziland)
Experiences were gained through consultation and, exchange dialogue;
According to the British Standard BS 8110-1:1997(Code of Practice for Reinforced
Concrete), which is reflective on codes in the SADC region; due to both technical exchange
and colonial legacy issues, there are two principal methods of construction [7] [8]:
1. Ribbed slabs without permanent blocks
2. Ribbed slabs with permanent hollow or solid blocks, (figure 2)
25
Figure 2: Ribbed Slabs-Construction Methods
The term “ribbed slab” therefore refers to in-situ slabs constructed in one of the following
ways:
a) Where topping is considered to contribute to structural strength:
1) as a series of concrete ribs cast in-situ between blocks which remain part of the
completed structure; the tops of the ribs are connected by a topping of concrete of the
same strength as that used in the ribs;
2) as a series of concrete ribs with topping cast on forms which may be removed after the
concrete has set;
3) with a continuous top and bottom face but containing voids of rectangular, oval or
other shape.
b) Where topping is not considered to contribute to structural strength: as a series of
concrete ribs cast in-situ between blocks which remain part of the completed structure; the
tops of the ribs may be connected by a topping of concrete (not necessarily of the same
strength as that used in the ribs).
c) Hollow or solid blocks and formers: may be of any suitable material but, however when
required to contribute to the structural strength of a slab, they should:
a) be made of concrete or burnt clay;
b) have a characteristic strength of at least 14 N/mm2, measured on the net section, when
axially loaded in the direction of compressive stress in the slab;
d) Spacing and sizing of ribs
1) The centres of the ribs should not exceed 1.5m
2) The depth of the ribs excluding topping should not exceed four times their average
width
3) The minimum rib width should consider cover, bar spacing and fire requirements.
4) The thickness of structural topping should not be less than 50mm or one-tenth clear
distance between ribs.
e) Design Considerations: Shear forces and moments for ribbed slabs may be analysed as a
series of T-beams with flange width equal to the distance between the ribs. Detailed design
code requirements are not the focus of this presentation, as these vary with countries or geo-
political regions.
OBSERVATIONS
The use of precast or semi-precast construction or in an otherwise in situ reinforced concrete
building is quite common in South Africa and the SADC region. There are various
proprietary precast and prestressed concrete floors on the market. Precast floors can be
designed to act compositely with an in situ structural topping, although the precast element
can carry loads without reliance on the topping. Design using proprietary products should be
carried out closely in conjunction with the particular manufacturer.
26
The paper presents a case study, on the authors’ research and experiences with a proprietary
Insudek-Mokete™ ribbed slab and waffle-raft system. Since its launch twelve years ago, the
Insudek/Litedek slab system has been used in over 2 000 000m2, in Southern Africa; in
projects ranging from commercial, institutional, residential and industrial buildings. The
system for insitu-concrete flooring system consists of light metal channels with prefixed
reinforcement; see figure 1 (insert 3 and 4). High density polystyrene blocks are rebated to fit
between the channels forming a permanent shutter for the casting of a +/-65mm structural
topping. The system can be designed as either one or two way spanning (waffle-raft slab). A
comparison of the system with normal reinforced solid slabs is shown below; Table 1. The
slab self weight or dead load is a measure of the amount of concrete weight imposed the
building structure, before other loads like finishes and live loads come into play.
Table 1: Insudek-Mokete Dead Load Structural Comparison with Solid Slabs.
(SELF-WEIGHT) DEAD LOAD TABLE:
Slab Depth Structural 150mm Rib 225mm Rib 300mm Rib Solid Slab
Thickness (mm) Topping
(mm) kN/m2 kN/m2 kN/m2 kN/m2
210 60 2.10 2.41 2.66 5.04
230 60 2.18 2.52 2.81 5.52
255 65 2.37 2.76 3.08 6.12
285 65 2.48 2.93 3.30 6.84
300 60 2.44 2.93 3.33 7.20
325 65 2.63 3.17 3.60 7.80
340 60 2.58 3.16 3.63 8.16
400 60 2.81 3.51 4.08 9.60
450 60 2.99 3.80 4.46 10.80
500 60 3.07 4.09 4.83 12.00
550 60 3.36 4.38 5.21 13.20
Rib Spacing c/c - 650mm 725mm 925mm N/A
DISCUSSION OF OBSERVATIONS
Reinforced-concrete is a composite construction material, in which, concrete is designed
for its high-compressive strength characteristics and the embedded steel for its high-
tension capacity; in such a manner that the two materials act together in resisting forces.
The reinforcing steel-bars, or mesh absorbs the tensile, shear, and sometimes the
compressive stresses in a concrete structure. Plain concrete does not easily withstand
tensile and shear-stresses caused by wind, earthquakes, vibrations, and other forces and
is therefore unsuitable in most structural applications. In reinforced concrete, the tensile
strength of steel and the compressive strength of concrete work together to allow the
member to sustain these stresses over considerable spans. However a considerable
amount of concrete in solid slabs, within the tension zone is redundant, as steel-
reinforcement provides the tension capacity
Figure 3, is reflective of the significant weight reduction achieved from lighter and stiffer
slabs, capable of achieving up-to 60% less concrete usage which is desirable as ‘green
building’ sustainable construction technology. This increases concrete and economic
savings in the overall structure.
27
Figure 3: Graph-Insudek-Mokete Dead Load Structural Comparison with Solid Slabs.
It is noted that, there are other different proprietary rib-and–block systems on the market,
however an exhaustive study of all systems, is not the objective of this study. The
presentation above is indicative only, and highlights practical examples and the existence of
concrete technologies that are cleaner, use less energy and more sustainable to the
environment.
CONCLUSION
According to Kuchena and Usiri (2009), the creation of low-energy ecological habitats is a
key component to sustainable development [4]. The design of the housing and the use of the
materials have to correspond to local building traditions and to the user group’s way of living.
Religious and cultural traditions have a great influence on this and have to be included in the
planning process. As Reddy-Venkatarama B. V. (2004) says, “building materials and
technologies, and building practices have evolved through ages. Housing and building
conditions reflect the living standards of a society. Energy consumed in
the manufacturing processes – energy intensity; Problems of long distance transportation;
Natural resources and raw materials consumed; Recycling and safe disposal; Impact on
environment, and Long-term sustainability . Thus the issues related to energy expenditure,
recycling, biodegradable, environmental sustainability with respect to future demand needs to
be addressed during the manufacture and use of any new building material” [13]. Therefore
introducing new sustainable construction technologies, it is important that it is not deemed as
a type of houses only for low-income families. Social impact and effect of status, is in this
case very important. People with a low income do not want to live in houses labeled only for
low-income people, because then everybody knows that the persons living in these houses are
poor. The standardization of technology is imperative to such communities to manage
perceptions. Lower income groups tend to copy the houses of the rich, which also is one of
the reasons why it is important that adoption of sustainable technologies must be
implemented at all levels. As the developed world adopts low-carbon footprint housing
systems this sets in motion a paradigm shift from the obsession of steel and concrete, towards
Slab Thickness (mm)
Dead
L
oad
kN
/m2
28
a realization that communities are already endowed with natural resources it is the
beneficiation knowledge systems which remain largely untapped.
ACKNOWLEDGEMENTS
The authors would like to acknowledge the assistance of Mokete Africa Holdings CC. for
availing information on their proprietary “Insudek” slab system.
BIBLIOGRAPHY
[1] Ballad, G. and Howell, G., 2006. “Introduction to Lean Construction: Work Structuring
and Production Control”, Lean Construction Instituite, www.leanconstruction.org
[2] Kuchena, J.C. and Chakwizira, J., 2004. “ Appropriate Low Cost Building Materials in
Zimbabwe”, Paper Presentation, International Conference on Alternative Technologies,
NUST, Bulawayo, Zimbabwe
[3] Kuchena, J.C. and Usiri, P. 2009 "Sustainable Advanced Construction Technologies", 4th
International Conference on EcoMaterials (ECOMAT 4, 2009), 24-27 November 2009, Bayamo,
Cuba
[4] Kuchena, J. C., and Usiri P., 2009. ”Low Cost Construction Technologies and Materials
– Case Study Mozambique”, Proceedings of the 11th Interantional Conference on Non-
conventional Materials and Technologis (NOCMAT 2009) Bath UK.,Sept. 2009
[5] Green Building Council South Africa, http://www.gbcsa.org.za/home.php
20012/07/01(11:00AM)
[6] Ministry of Local Government and Housing, Zimbabwe 1981, “Model Building By-Laws
(Amended)”, Government Printers,
[7] The Institution of Structural Engineers, 1989 “Standard Method of Detailing Structural
Concrete”. The Concrete Society, Published by the Institution of Structural Engineers
[8] The Institution of Civil Engineers, 2002, “Manual for the Design of Reinforced Concrete
[9] Building Structures”, 2ND
Edition, Published by, The Institution of Structural Engineers
[10] Usiri, P, 2011. “The Design and Development of Energy Efficient Buildings “,The National
Infrastructure Asset Management Conference 2011, 22th-23
th June 2011,Harvard Training Institute
,Johannesburg
[11] Van Wyk, L. and Kuchena,J. 2008. “Low-income Housing and Sustainability in South
Africa:A Case Study Housing Planning & Research – E. Cape”, Paper & presentation,
Proceedings of SAHF (South Afraican Housing Foundation Int. Conference, Cape Town,
SA
[12] Van Wyk, L. 2008. “Developing and maintaining a South African construction
manufacturing capability: lessons from the automotive industry”, ACTP (Advanced
Construction Technology Platform), Technical Report, CSIR, SA
[13] Van Wyk L. 2009. “ACTP (Advanced Construction Technology Platform)”,
Presentation Report to the RAP (Research Advisory Panel), CSIR, SA
[14] Venkatarama-Reddy, B. V. 2004, “Sustainable building technologies,” Current
Science: Special Section: Application of S&T to Rural Areas Volume 87, No. 7.
29
APPROPRIATE ARCHITECTURE FOR SUSTAINABLE
DEVELOPMENT: THE CREATION OF ECOLOGICAL FOOTPRINT
AND HUMAN DEVELOPMENT INDEX CAPABILITY
Jeremy Gibberd
Built Environment Unit, CSIR, Pretoria, South Africa, [email protected]
Keywords: Sustainable Development, Ecological Footprint, Human Development Index
Abstract
Carbon emission scenarios are used as key inputs in the sustainability and built environment
strategies and policies. Decisions and direction in these are based on carbon emission
models which show the optimum mix of interventions required to achieve carbon emission
reductions or stabilization.
Reducing carbon emissions however does not lead sustainability. Sustainability is more
complex and requires the achievement of minimum quality of life standards as well as a
balance between environmental and human systems. The danger with a focus on carbon
emissions is that limited resources and timeframes may be exhausted trying to achieve
reductions and valuable opportunities to build long term sustainable solutions will be being
lost.
This paper argues that increasingly scarce resources, the timeframes for addressing climate
change and the lifespan of infrastructure and buildings (50+ years) mean that we cannot
address carbon emission reductions first, and then address sustainability later; we need to
address both at once. We need to develop appropriate architecture for sustainable
development and not just carbon emission reduction.
The paper draws on a definition of sustainability developed by the World Wildlife Fund to
show how a sustainable development approach can address carbon emissions while building
more sustainable systems. It proposes a built environment sustainability framework and
shows how this can be used to assess built environments and identify appropriate mixes of
interventions to improve the sustainability performance of built environments. It also
provides an indication of the type of appropriate architecture for sustainable development
envisaged by this framework.
INTRODUCTION Carbon emission projections are widely used in both developed and developing countries to
inform development strategies and policy. Projections are used to identify the most
appropriate interventions required to achieve carbon emission stabilisation or downward
trajectories to in order to meet global or national targets. Selected interventions then form the
basis of key national development frameworks (Barker 2007) (Winkler 2007).
There are, however, problems with using carbon emissions as the key input into development
strategies. Increasing carbon dioxide levels in the atmosphere are a symptom of imbalance in
planetary systems and, as with the human body, a sole focus on addressing symptoms, may
not lead to a cure.
30
A focus on addressing carbon emission symptoms often results in the selection of
standardised technological solutions such as renewable energy or solar water heaters which
can be easily modeled, and uniformly applied. These solutions however may not take into
account pressing local social and economic circumstances. This results in the selected
solutions not being implemented as these are not seen as a local priority and therefore are
seen as inappropriate. Alternatively, if these are implemented, the technological solutions
(often imported) consume valuable resources that are then not available to address local
social and economic issues.
This approach is reflected in green building rating tools which emphasize technological
solutions such as improved artificial lighting, efficient air-conditioning systems and
renewable energy. This however assumes that this technology is available and affordable. It
also assumes that there is the technical capacity and ongoing funding to install and maintain
these types of installations. This is obviously not the case in many developed countries, as is
demonstrated in the case study, later in the paper.
This paper argues that it is important to respond directly to local situations and build local
systems with a view to long term sustainability. Instead of addressing symptoms of
environmental imbalance with partial solutions, we must develop human and environmental
systems which work together to achieve sustainability. For this, a definition of sustainability
that both captures of the key characteristics of human and environmental systems and can be
easily applied to the built environment, is required [1].
Defining Sustainability A suitable definition of sustainability has been developed by the World Wildlife Fund
(WWF). This describes sustainability as being the achievement of above 0.8 on the Human
Development Index (HDI) and the achievement of an Ecological Footprint (EF) below 1.8
global hectares per person [2].
The Human Development Index was developed by the United Nations as an alternative to
economic progress indicators and aimed to provide a broader measure that defined human
development as a process of enlarging people’s choices and enhancing human capabilities
[3], The measure is based on:
A long healthy life, measured by life expectancy at birth
Knowledge, measured by the adult literacy rate and combined primary, secondary, and
tertiary gross enrolment ratio
A decent standard of living, as measure by the GDP per capital in purchasing power
parity (PPP) in terms of US dollars In order to measure the Human Development Index, minimum and maximum values
(goalposts) are chosen for each of the above indicators. These goalposts are outlined below:
Dimensional indicator Maximum value Minimum value
Life expectancy at birth 85 25
Adult literacy rate (%) 100 0
Combined gross enrollment
ratio (%)
100 0
GDP per capita (PPP US$) 40,000 100
31
The Human Development Index is the average of three dimensional indexes:
HDI = 1/3 (life expectancy index) + 1/3 (education index) + 1/3 (GDP index)
An Ecological Footprint is an estimate of the amount of biologically productive land and sea
required to provide the resources a human population consumes and absorb the
corresponding waste. These estimates are based on consumption of resources and production
of waste and emissions in the following areas:
Food, measured in type and amount of food consumed
Shelter, measured in size, utilization and energy consumption
Mobility, measured in type of transport used and distances travelled
Goods, measured in type and quantity consumed
Services, measured in type and quantity consumed
Waste, measured in type and quantity produced
The area of biologically productive land and sea for each of these areas is calculated in global
hectares (gha) and then added together to provide an overall ecological footprint [4].This
measure is particularly useful as it enables the impact of infrastructure and lifestyles to be
measured in relation to the earth’s carrying capacity of 1.8 global hectares (gha) per person.
National Development Trajectories National figures using the Human Development Index and Ecological Footprint have been
combined in graph, shown below.
Figure 1 National Development Trajectories [3]
32
This shows that countries in Europe and North America very high Ecological Footprints and
acceptable Human Development Indexes (above 0.8), while countries in Africa have
unacceptably low Human Development Indexes (below 0.8) but have Ecological Footprints
within the biosphere’s allowable capacity per person.
The graph also indicates national development trajectories (the lines between the diamonds
and dots). For example, the trajectory of the USA has been steep, with a large increase in
their ecological footprint and relatively limited improvement in their Human Development
Index in the last 20 years. In contrast, Hungary, over the same time period, has improved
their Human Development Index to achieve the minimum sustainability criteria and, at same
time, reduced their ecological footprint.
This suggests that strategies based on an understanding of current HDI and EF performance
can support a shift towards sustainability [5].This is supported by Holden et al (2007) who
argues, through reference to purchasing price parity and ecological footprint measures, that
developing and developed countries require different strategies to achieve sustainability [6].
There is therefore a strong argument that built environment development strategies should
respond to local EF and HDI performance and, through the provision of appropriate
characteristics, support development trajectories aimed at achieving sustainability.
Minimum Standards and Built Environment Characteristics
The tables below interpret Ecological Footprint and Human Development Index criteria into
minimum standards. The built environment characteristics required to achieve these
minimum standards are then listed in the last column.
Table 1 Ecological Footprint, Minimum Standards and Built Environment Characteristics
Ecological Footprint Criteria Minimum
Standards
Built Environment
Characteristics
Food: Measured in type and
amount of food consumed
Occupants can meet their
nutritional requirements
through affordable, low
ecological footprint means.
Local markets with low
ecological footprint foods.
Ability to produce low
ecological footprint food.
Shelter: Measured in size,
utilization and energy
consumption
Occupants can meet shelter
requirements through
affordable, low ecological
footprint means.
Appropriately sized, resource
efficient accommodation.
Mobility: Measured in type of
transport used and distances
traveled
Occupants can access daily
requirements using low
ecological footprint means.
Daily requirements accessible
within walking distance.
Access to local public transport.
Goods: Measured in type and
quantity consumed
Occupants can access
required goods through
affordable, low ecological
footprint means.
Appropriate goods available
locally.
Facilities to support efficient
usage / shared use of goods.
Services: Measured in type and
quantity consumed
Occupants can access
required services through
affordable, low ecological
footprint means.
Appropriate services available
locally.
Facilities to support efficient
usage of services.
33
Table 2 Human Development Index, Minimum Standards and Built Environment
Characteristics
Human Development Index
Criteria
Minimum
Standards
Built Environment
Characteristics
Health: A long healthy life, measured
by life expectancy at birth
Occupants can access
facilities required for
health.
Access to sports, health, leisure
facilities.
Access to healthy food and clean water.
No local hazards such as violent crime
and pollution.
Knowledge: measured by the adult
literacy rate and combined primary,
secondary, and tertiary gross
enrolment ratio
Occupants can access
facilities required for
learning and education.
Access to primary, secondary, tertiary
and ongoing learning facilities.
Standard of Living: A decent
standard of living, as measure by the
GDP per capital in purchasing power
parity (PPP) in terms of US dollars
Occupants can access
opportunities to enable a
decent standard of living.
Access to employment opportunities.
Self employment opportunities.
Access to support for small enterprise
development.
The Study Area
In order to understand the built environment characteristics listed in the Tables 1 and 2, these
are translated into built environment sustainability criteria, shown in Table 3.
These criteria are then used to evaluate an area of Atteridgeville, a suburb of Pretoria. The
study area is typical of many urban areas in South Africa and consists of self-built informal
housing constructed in a loosely planned grid. Only basic infrastructure in the form of water
(brought in by tankers) and some graded roads exists. Other infrastructure, such as street
lighting, storm water drainage, piped water, electricity, parks, schools, health facilities,
sports, leisure and retail facilities is limited or may not exist locally.
The built environment sustainability criteria were applied to a household (red rectangle) in
the centre of the study area. Rings of 1km, 2km and 3km were then marked on the study area
plan, indicated in Figure 2. A survey of the household and area using the criteria was then
carried out.
Figure 2. Study area. Red rings indicate 1, 2 and 3 km distance from household
location (red dot)
34
The results of this assessment using the Built Environment Sustainability Tool (BEST) are
captured under the ‘Existing’ column in Figure 3 below, in accordance with the following
key. An ‘0’ indicates the existence of the specified built environment sustainability criterion
on site or within a 3 km radius of the site, a ‘5’ indicates that this does not exist and a ‘3’ that
the criterion is partially fulfilled. For each set of built environment sustainability criteria,
such as ‘Health’, an average value is provided in red; in this case it is 4.20. This average
score provides an indication of the built environment capability within the respective areas,
with a low score (near 0) indicating strong capability and a high score (near 5) weak
capability.
The BEST results show that the site’s built environment capability to support EF and HDI
targets is particularly weak in the areas of ‘Goods’, ‘Knowledge’ and ‘Standard of Living’,
which all have an average of ‘5’. The best performing area was ‘Waste’ with a value of 1.67.
These results are also shown in a spider diagram in Figure 2 (the blue line). These results can
be used to diagnose gaps and prioritise interventions. In this case, built environment
capability gaps exist in ‘Knowledge’, ‘Standard of Living”, and ‘Goods’ and interventions to
address these should be prioritised.
Overall BEST measures of the HDI and EF capability can also be derived. Figure 3 indicates
that the site has an EF capability of 3.43 and an HDI Capability of 4.73. The BEST also
shows that the combined built environment capability is 4.08. This suggests that the site has
a very low capability to support the achievement of HDI sustainability targets. It also shows
that while the site has a better capability to support the achievement of EF targets, this is still
very poor. These BEST capability measurements reflect South Africa’s location shown in
Figure 1.
Appropriate Architecture for Sustainable Development Given the baseline results, what would be suitable interventions to support sustainability in
this area? What would be ‘appropriate architecture for sustainable development’ in this
location?
In order to begin to develop and evaluate ideas a number of options were introduced into the
tool and the impact assessed. These interventions are listed below:
Urban Gardens: Provides access to local food gardens.
Tool Hire: Provides access to local tool and equipment hire or sharing.
Urban Market: Provides access to local markets for food and goods.
Solar Water Heating: Provides solar water heating to houses.
Local Multipurpose School: Provides access to a preschool, primary
and secondary school and a learning resource centre with information
and communications technology and support for ongoing learning.
Rainwater Harvesting: Provides rainwater harvesting systems to
houses.
35
Table 3 Built Environment Sustainability Tool (BEST)
The overall impact of the interventions in terms of improved built environment capability
was ascertained from BEST total scores. This indicates that ‘Urban Gardens’, ‘Urban
Markets’, and ‘Multipurpose School’ have the highest BEST scores at 32, 32 and 40
respectively, and that ‘Tool Hire’, ‘Solar Water Heating’ and ‘Rainwater Harvesting’ have
the lowest, at 9, 8 and 10, respectively.
36
The BEST results are surprising as show they indicate that conventional greening
interventions such as the installation of solar water heaters, water efficiency programmes and
energy efficient housing may have a lower impact on local sustainability than urban
agriculture, multipurpose learning centers and local markets.
Conclusion
The paper concludes that the investigation into the implications of the HDI-EF definition of
sustainability for the built environment in a developing country is a valuable exercise and
leads to innovative and surprising results.
Translating the definition into a tool (the Built Environment Sustainability Tool) provides an
innovative and original way of assessing the sustainability of urban environments. This tool
can not only be used to assess the sustainability of urban environments but also the impact of
potential interventions. This makes it highly valuable as a planning decision support tool.
The findings of using the tool are surprising in that they suggest that conventional greening
interventions such as the solar water heater and water efficiency programmes may be less
effective in improving the sustainability of a developing country communities than the
development of urban agriculture, local markets and local multi-purposes community
learning resource centres. While this is unexpected, a more detailed understanding of the
local context and a deeper understanding of sustainability suggests that this finding is
accurate and therefore the tool could be used to improve development planning and decision-
making.
Further research on the tool and potential sustainability interventions should be carried out in
order to understand how more responsive and appropriate architecture for sustainable
development can be developed.
REFERENCES [1] Curwell, S. et al., 2010, The implications of urban sustainability. Building Research &
Information, (January 2012), 37-41.
[2]World Wild Life Fund, 2006, The Living Planet Report. Accessed from
www.panda.org/news_facts/publications/living_planet_report/linving_planet_report_timeline
/index.cfm
[3] United Nations Development Programme, 2007, Human Development Report 2007/2008.
United Nations Development Programme, New York.
[4]Wackernagel, M. and Yount, D., 2000, Footprints for Sustainability: the Next Steps.
Environment, Development and Sustainability 2, Kluwer Academic Publishers, 21-42.
[5] Moran, D.D. et al., 2008. Measuring sustainable development — Nation by nation.
Ecological Economics, 64(3), 470-474.
[6] Holden, E. & Linnerud, K., 2007, The Sustainable Development Area: Satisfying Basic
Needs and Safeguarding Ecological Sustainability. Sustainable Development, 187(October
2006), 74-187.
37
Sustainable Exploitation and Usage of Locally Available Building Materials
in Western Kenya
Robinson Onyango Manguro
Architect, Ministry of Public Works, P.O Box 152 - 00515, Buruburu, Nairobi, Kenya, Tel +
254721286228, Email: [email protected]
Keywords: construction, building materials, sustainable, exploitation, usage
Abstract
The construction industry in Kenya has undergone quite a considerable amount of growth
with the turn of the millennium. This has seen the use of construction of materials, both
locally available and imported. The local materials have however been used all around
without much information being shared on the source and the distribution of the various
material across the country. Traditional materials which are readily available have not been
well used much due to lack of this information as well as legislation. Another major
challenge facing the sustainable use of materials on Kenya is the poor legislation. This starts
from the point of exploitation to the usage of these materials. With effects of climate change
being felt all over the world, there is need to ensure that the exploitation and use of building
materials is sustainable. This research paper has taken up the task of identifying the various
sources of the locally available materials and their usage with special emphasis on Western
Kenya. The paper highlights their properties and suggesting ways of improving their
exploitation and usage in a sustainable manner: economically, environmentally, functionally
and aesthetically. After mapping out the locally available building materials detailing their
cost and functional qualities, those that need to be further developed will also be identified so
as to ensure more sustainable materials are used locally.
Introduction
Kenya has experienced considerable growth in the building industry which has become a
major driver of the economy in the last decade. Apart from the joint building council prices,
the local industry does not have a range of documentation on the availability and sustainable
use of building materials in various parts of the country. This has led to people haphazardly
using the building materials in a manner that is less sustainable economically and
environmentally. Locally available building materials have been exploited without
consideration for future users. Western Kenya has seen an increase in construction activities
in the past few years. In the age of climate change, every sector of the economy has a duty to
promote sustainability. So much environmental degradation is happening as a result of
construction activities and one way of cutting this is through the sustainable use and
exploitation of building materials more so the ones that are locally available. There is need to
adequately inform such a process and help ease the pressure on the economy and the
environment.
This paper deals with materials that are used in the sub structure and super structure and will
not dwell much on the interiors of buildings. The materials are sampled in three counties in
Western Kenya namely Kisii, Homa Bay and Kisumu.
Kisii County is located to the south east of Lake Victoria; A high percentage of its population
relies on agriculture and the setting is mainly rural. The town has experienced a high rate of
urban activities and construction is one major driver of the economy in the area.
38
Homa Bay County is located to the south of Lake Victoria and has been long known as the
headquarters of South Nyanza; For long, the town’s potential has been underutilized due to
poor road network but rapid urbanization can be observed with the improved road network
and impending devolution of government. Construction of modern structures is a major
activity currently.
Kisumu County is located to the east of Lake Victoria and has been long known as the
headquarters of Nyanza and widely viewed as a major town in Western Kenya; It is mainly
an urban area with neighboring rural settlements which rely on fishing and small scale
agriculture. Seen as a major hub connecting the other east African countries namely Rwanda,
Burundi, Uganda and North western Tanzania to Kenya, it is a fast growing town.
Construction of modern structures is a major activity currently.
Even though the chosen region is wide and it would have been necessary to study more
counties, it is important to note that these counties have a number of locally available
building materials and is representative of the region.
Locally Available Materials
Green Materials
Because building materials constitute a large part of the environmental burden created by a
building, the use of green building materials and products is one of the several constituents
that make a building sustainable. Extracting materials from the earth and processing them
into a finished product require energy and water resources and produce waste, some of which
may be hazardous.
Some products give off toxic gases after installation. Others require cleaning with chemicals
that may do likewise. Postconsumer disposal of products consumes landfills, some of which
may pollute groundwater. Materials whose overall environmental burden is low are referred
to as green materials. The relative greenness of a material is based on the same basic
determinants as for the building as a whole. More specifically, the greenness of a material is a
function of the following factors:
• Renewability
• Recovery and reusability
• Recyclability and recycled content
• Biodegradability
• Resource (energy and water) consumption
• Impact on occupants’ health
Figure iii: Map of Africa and Kenya, study area is around Lake Victoria in western Kenya
39
• Durability and life-cycle assessment of greenness
Building Materials
Natural Stone
Natural stone has been used majorly in Kenya as a load bearing member especially for the
walls both in the foundation and the super structure. This is due to the great structural
strength that it possesses. Properties of stone that need to be tested are appearance, strength,
porosity, absorption and permeability, temperature and moisture movement, fire resistance,
resistance to wear and chemical action. Some stones are used as they come from the quarry
with the face unchanged while others are cut to the size needed for final installation. They
can also be further smoothened and dressed on site.
Natural stone can also be broken down into aggregate. Aggregate is the granular material,
such as sand, gravel, crushed stone, crushed blast-furnace slag, or construction and
demolition waste that is used with a cementing medium to produce either concrete or mortar.
The term coarse aggregate refers to the aggregate particles larger than 4.75mm (No. 4 sieve),
and the term fine aggregate refers to the aggregate particles smaller than 4.75mm but larger
than 75µm (No. 200 sieve). Gravel is coarse aggregate resulting from natural disintegration
by weathering rock. The term sand is commonly used for fine aggregate resulting from either
natural weathering or crushing of stone. Crushed stone is the product resulting from industrial
crushing of rocks, boulders, or large cobblestones. Iron blast-furnace slag, a by-product of the
iron industry, is the material obtained by crushing blast-furnace slag that solidified by slow
cooling under atmospheric conditions. Aggregate from construction and demolition waste
refers to the product obtained from recycling of concrete, brick, or stone rubble.
Aggregates have considerable influence on the strength, dimensional stability, and durability
of concrete. In addition to these important properties of hardened concrete, the aggregate also
plays a major role in determining the cost and workability of concrete mixtures. Natural stone
is also used as a finish to walls, floors and working surfaces.
Concrete
Concrete in its simplest basic form consists of a mixture of cement, ballast/stone, sand and
water. (Ballast and sand are collectively known as aggregate). Depending on the specified
requirements during serviceability, certain admixtures could also be added as a further
component of the concrete mix. Concrete is the only major building material that can be
delivered to the job site in a plastic state. This unique quality makes concrete desirable as a
building material because it can be molded to virtually any form or shape.
Concrete can be moulded as blocks and used for building walls, either load bearing or non
load bearing in a framed structure. Concrete tiles have also become a common type of roofing
material used widely in the country. This has gained popularity due to its light weight
compared to clay roofing tiles. They are also considered fairly safe for rain water collection.
Reinforced Concrete is due to the fact that concrete is very brittle when subjected to normal
tensile stresses and impact loads. There has always been a need to add reinforcement to
concrete to compensate for this lack of ductility. In many cases, the concrete member is kept
intact using steel bars or welded wire fabric reinforcement in one or two locations of
potentially high stress. If the concrete cracks, the concrete is hinged together at those limited
locations.
40
Clay
They have ability to be crushed and mixed with water to form a plastic material which can be
moulded into various shapes. This can then be fired to high temperatures from which they
attain a hard, weather resistant characteristic.
Fired clay bricks remain one of the most enduring building materials known to the world
wide building industry. Some might argue that it is also one of the most beautiful and that it
adds character to any building with its colour, strength and texture. Being such a versatile
building material and because of its very good climatic characteristics, it remains the material
of choice for residential buildings. Bricks have an excellent fire rating, it is weatherproof and
has really good acoustic properties and is almost soundproof. Bricks also come in different
finishes and colours. This can be costly as the quality of different brick manufacturers vary
considerably as will also be reflected in the price. A very cheap brick might be of un-even
size or may warp making building with them a lot more difficult. This is mostly the case with
bricks that are burned locally in homemade kilns with minimal resources and expertise.
Interlocking bricks is becoming very popular and has been promoted as one of the most
economically sustainable materials. This is due to the fact that there is no need to use mortar
to fix this one brick to the other. The process of building is also quick as the bricks do not
need to be fired and the workmanship on site is fairly straightforward. This type of brick is
produced by mixing murram and small amount of cement in a special machine and they are
ready to use almost immediately.
Clay is also used to make roofing tiles which have remained popular especially for the high
end market due to the aesthetic and functional qualities. Many houses especially in the rural
and low income areas in towns are still made of mud walls, a traditional material used in
Kenya. This is due to its low cost, at times it costing the owners no amount of money for to
just scoop the naturally available clay soil and use it to make the walls after properly
kneading it.
Timber
In Kenya, timber is generally regarded as a secondary construction material, used only when
there are financial constraints or when the structure being built is temporary. Structural
timber is used extensively in roofing trusses for homes and institutions, mainly due to the
higher cost of alternative material such as steel. The extensive use of timber to construct
modern homes and as framing of large important structures such as concert halls, sports and
leisure centers has been hindered by several factors as listed below: -
i) Lack of proper technology and reference information for design and erection of
timber structures.
ii) Conservatism by many people who regard timber as a traditional material and
therefore unacceptable for modern structures.
iii) Lack of proper information on wood preservation has led to an over-estimation of the
hazards to structures by fungal and insect attack, leading to higher insurance and
mortgage premiums on timber structures.
iv) There is a general feeling that timber structures lack permanence and can only be
used on temporary structures.
v) Technological development in the use of other construction materials, especially
concrete and steel, has downgraded timber as a suitable alternative.
vi) Due to increased deforestation and the need to conserve the forests the authorities
have imposed a control on felling of trees and thus pushing timber prices up.
41
vii) Some structural customs force the use of a specific building material other than
timber, making timber unpopular in such areas.
Timber is widely used for window and door frames. These are used in all ranges of finishes,
from the lowly regarded off cuts to high grade well finished timber. Windows and door
materials also use timber.
Building Typologies
The buildings covered in this study are not limited to residential units but include Residential
Houses, Government Office buildings, Government Institutional buildings, Private
Institutional Buildings, Commercial buildings, Industrial Buildings and Other Buildings
within the residential home, industry, institutions or commercial centres, that might not fall in
any of the above categories and would bear distinctive characteristics for example are the
structures that are used as animal sheds.
Exploitation of materials
Masonary /Natural Stone
Aesthetics
Can be shaped and used to form decorative patterns
Function
Used for interior and external wall, cladding material, Fencing, Superstructure
Environmental sustainability Mining of natural stone is not properly protected and controlled. the Mining Act Cap 306 is
currently being reviewed. There is need to protect quarries from encroachment of human
settlements, otherwise there will be shortage of stone and ballast. The stone quarries are small
scale with neighbouring human settlements. Use of blasting machines would endanger the
lives of the neighbours with the stone debris reaching their homesteads. This means that the
miners have to use manual methods and cannot use machines to blast thereby the rock deposit
is not exploited to the maximum. When large deposits of underlying rock is left unexploited,
the space is left lying idle. With many sites being exploited halfway, there is danger of
exhausting the sources of natural stone which is one of the locally available materials.
The type stone mined locally is very hard and difficult to work on hence very labour
intensive. It is mined manually which makes it even more difficult to shape since they are not
machine cut. It ends up being used majorly for substructure hence some contractors prefer to
bring softer stones from further.
Figure ii Figure iii
42
Timber
Aesthetics
Majorly used for roofing trusses
Function
Can be finished to give rustic look
Environmental sustainability Timber used for building is reducing due to over exploitation of the material and dwindling
area of forest cover. The main use of timber in building is roofing trusses which use cypress.
However it is noted that the most locally available timber for construction is blue gum, which
is not structurally advisable in construction due to its poor seasoning characteristics. Steel is
also becoming a popular material, replacing timber trusses. The local population should be
sensitized about this fact and accordingly advised to embrace growing of other structurally
appropriate trees for timber e.g. cypress and pine. Hardwood which is normally used for
doors and other fixtures within the building is also in scarce supply.
Fired Clay Bricks
Aesthetics
Aesthetically appealing and offers a variety of surface treatments.
Function
Used extensively internally and externally in superstructure walling owing to its
availability.
Cladding material
Environmental sustainability
There exists no legislation to protect brick production. The bricks are manufactured in small
and large scale by the local people. The large scale manufacturers are however running out of
business and are unable to compete with the small scale producers. This is due to the fact that
the bricks produced at small scale are less expensive though they are of lower quality. The
users are not so keen on the quality and mind more about the pricing. A number of large scale
factories in the region have been forced to shut down because brick production is not viable
anymore but fired brick still remains the most popular material in the region. However there
are challenges posed by brick production especially at a small scale. Large areas that could be
used for farmland are being used for brick production hence causing a crisis of food security
especially in the drier years. There is another challenge of time taken to produce the bricks.
At some point, demand has surpassed the supply of the burnt clay bricks causing shortages
and this would lead to a crisis especially now that construction has been spurred by growth of
urban centres in the region due to government policy of devolution. Local brick production
uses firewood. This has promoted illegal logging of trees which leads to deforestation thus
making the burning of clay bricks at a small scale a potential source of environmental
disaster.
There is a problem with perception within the town area, where if it is used for walling it
reduces the perceived value of the building. The cost of using bricks can be expensive
(mortar, breakage and labour) if not done well and it requires a large area of walling to be
economical. For this reason it is used mostly in older buildings and private residential houses.
Another setback is that the Ministry of Public Works has not allowed use of bricks in its
43
projects even where it seems as the most viable option. Cost of using bricks is expensive
(mortar, breakage and labour) it requires a large area of walling to be economical.
Interlocking bricks are seen by the locals to be expensive to produce but is being promoted
by Ministry of Housing who are offering free labour for production and training to locals.
The potential is yet to be explored in the region.
Figure iv: Locally fired clay bricks Figure v: Decorated natural stone wall
Concrete Blocks
Aesthetics
Must be plastered and painted to give a nice finish
Function
Used for interior and external wall, Concrete paving blocks
Is not a popular material due to unreliability of the mix ratios and cost of cement
Natural stone and fired bricks preferred due to cost and availability
Environmental sustainability
Availability of ballast is minimal and the quarries have a very short life span if not checked.
There is no local manufacturer of cement and even the cement companies in Kisumu just act
as suppliers. The price is comparatively high since it is sourced from Nairobi, about 400km
away and some contractors find it cheaper to source it themselves from Nairobi in bulk.
There are however concrete block manufacturers locally in Kisumu and despite the
challenges of the mix ratio and quality control, it is increasingly becoming popular due to its
comparatively lower price. This is because the other ingredients are available locally ie
quarry dust, ballast and chippings. The same challenges caused by stone mining are posed by
the quarries that supply the ballast and quarry dust.
Conclusion
Construction industry has been recorded as one of the major drivers of Kenya’s economy and
luckily the country has a variety of locally available building materials which must be
exploited and used sustainably if they are to benefit the current as well as the future
generations. The government must speed up the process of streamlining the relevant
legislation that will ensure the construction materials are protected as part of the natural
resources in the country.
As the materials are being exploited and the environmental issues are coming to the fore, all
players must be actively involved in protecting the materials as well as the environment.
44
There is need to further develop some of the building materials to ensure that they are well
used and can withstand the test of time for example, fired clay bricks, if manufactured
properly can last for a long time and rated as a building material for permanent housing.
Acknowledgements
The author would like to acknowledge Architect Helen Kinuthia, Engineer Andrew Kimatu
and QS Ambrose Kiragu for support during the field study which was supported by the
Kenya Building Research Centre, a department of the Ministry of Public Works, Kenya.
References
[1] Campbell P.A, Timber for Building in Tanzania, Forest Department, Ministry of
Natural Resources and Tourism, Tanzania (1971)
[2] Mehta P.K., Monteiro P.J.M. Concrete: Microstructure, Properties and Materials, Tata
McGraw Hill, New Delhi, 3rd
edition, Pg. 168-175, 253-279, (2006)
[3] Geeson, A. G, Revised by Geeson C, Building Science Materials, for Students of
Architecture and Building Volume2, English University Press, (1967)
[4] BRE Digests).Building Materials, MTP Construction. (1973
[5] Watson D. A., Construction materials and Processes, Mc Graw-Hill. (1978)
[6] Hasegawa T. Environmentally Sustainable Buildings: Challenges and Policies, pages
190, 63, 87, OECD Publishing, (2003)
45
STRENGTHENING COMMUNITY BASED EROSION PROTECTION
PRACTISES WITH ENVIRONMENTALLY-FRIENDLY SISAL
GEOTEXTILES.
1Abraham B Nyoni and
2Tafadzwa T Sango
1 National University of Science and Technology, Department of Textile Technology
PO Box AC 939 Ascot, Bulawayo, Zimbabwe
Fax: +263. E-mail: [email protected] 2
National University of Science and Technology, Department of Textile Technology
PO Box AC 939 Ascot, Bulawayo, Zimbabwe
Key words: erosion, slope gradient, sisal, geotextiles, degradation
Abstract
Land degradation is one of the most visible aspects of environmental source depletion in
developing countries. It is normally manifest in declining productivity of land and
deteriorating quality of the physical environment. A common manifest of acute land
degradation is the development of wasteland through continued loss of land resources in the
form of soil erosion. This type of degradation has become an enduring feature of most urban
and rural environments in Southern Africa. The event of land degradation is particularly
evident in areas where the animal and human carrying capacities of ecosystems have been
exceeded, vegetation has been depleted and in slopping areas leading to extensive areas of
sheet and splash erosion.
The effectiveness of an erosion control geotextile is its ability to provide temporary erosion
control until natural vegetation, such as root formation establishes cover. The viability of
using a fabric made from Agave Deserti Sisal fibre as an erosion control geotextile was
conducted using a rainfall simulator and the sisal degradation period studied by burying
fabrics into an open field and periodically (weekly) testing the tensile strength of the
constituent yarns. The fabric samples were exposed to natural conditions and watered
according to seasonal rainfall predictions for the period of the research. Results show that
due to the sisal fabric structure (aperture size) and gradient, the fabrics provided a cover
factor ranging from 0.21 at 11.30 gradient to 0.74 at 45
0 gradient. Results for the
degradation experiment show that the percentage strength loss of the sisal fabric was 88.04%
after 7 weeks. This indicates a continuous degradation of the fabric therefore, before the
fabrics degrades completely it can provide temporary cover until vegetation establishes
necessary cover and protection.
Introduction
Rampant soil erosion is threatening the long-term viability of large areas of land in
Zimbabwe. The risk of losing soil fertility is increased and thus the productivity of the land is
decreased. There is also a large risk of over-sedimentation in rivers, lakes and reservoirs, as a
result of soil erosion, which therefore affects water supply [1].
Soil erosion is a two-phase process consisting of the detachment of individual soil particles
from the soil mass and their transport by erosive agents such as running water and wind. A
third phase, deposition, occurs when there is no longer energy to transport the particles [2].
Climatically Zimbabwe is characterised by a mono-modal rainfall regime which is associated
with the annual migration of the inter-tropical convergence zone (ITCZ). The ITCZ stretches
across central Zimbabwe from December to February allowing the dry trade winds and
extremely moist equatorial air masses to converge. As a result the bulk of the rain falls in the
46
form of heavy convectional downpours [3]. The rain drops falling causes a type of erosion
called splash erosion. As the name suggests, splash erosion is the spattering of small soil
particles caused by the impact of raindrops on wet soil. Sheet erosion then takes place, as a
fairy uniform layer of top-soil, is gradually removed by run-off water [2] and is more
effective at a gradient. The rate and magnitude of erosion by rain water is controlled by
rainfall intensity and runoff, soil erodibility, vegetation, slope gradient and length [2,4].
Erosion Control Technologies Reliable and proven soil conservation technologies include ridge-planting, no-till cultivation,
crop rotations, strip cropping, grass strips, mulches, living mulches, agro-forestry, terracing,
contour planting, cover crops and windbreaks [5]. All conservation methods generally reduce
soil erosion rates by maintaining or facilitating vegetative cover over the soil.
In some countries new technologies, relative to the traditional methods, are being
implemented to reduce the effect of soil erosion. New technology has brought the use of geo-
textiles in soil erosion control. Geotextiles are woven, knitted or non-woven textiles used in
or near the ground to enhance the ground’s characteristics. Different fabric composition and
construction are suitable for different applications such as filtration, drainage, separation,
reinforcement, moisture barrier, and erosion control [6,7,8].
Geo-textiles can reduce runoff, retain soil particles and protect soil which has not been
vegetated, from the sun, rain and wind. They can also be used to suppress weeds around
newly planted trees. Erosion control can be applied to riverbanks and coastlines to prevent
undermining by the ebb and flow of the tide or just by wave motion [1].
Geotextiles have been used for many years for various applications such as roadway
construction in the days of the Pharaohs using natural fibres only, to a variety of modern day
uses using not only natural fibres but synthetic and composite fibres.
(a) (b)
Figure Error! No text of specified style in document.1 Natural fibre geotextile applied on
bare ground (a) and plants growing (b) [9]
47
Theoretical experiments
Table 1 Physical Properties of fabric samples
Fabric
Physical property Vm1 Vm2 Vm3
Count (Ktex) 3.4 3.4 3.4
Aperture size (mm2) 10 x 10 15 x 15 20 x 20
Mass per unit area (g/m2) 340 227 170
The yarns were spun by the bunching and rolling method and woven into three fabrics with
aperture sizes; 10mm, 15mm and 20mm using the frame shown in Figure 2. The aim of the
aperture sizes was to determine the most suitable fabric structure that would provide an
effective cover factor that is, minimise the ratio of soil loss from a protected slope compared
to the soil loss from an unprotected slope.
Weaving frame –Three 0.5m x 1.0m frames were constructed (Figure 2) using wood and
nails. The nails were spaced 10mm, 15mm and 20mm apart and the woven fabrics were
labelled as fabric Vm1, Vm2 and Vm3 respectively.
Procedure
a) Warm water was used to wet yarns to make them soft and pliable;
b) The yarns were interlaced ensuring that they are pulled tightly across the frame;
c) The woven fabrics were left to dry for 45 minutes.
Figure 2 Weaving frame
48
Degradation
The rate of fabric degradation was determined by periodically (weekly) testing the tensile
strength of constituent warp and weft yarns of the unearthed fabrics using the Instron Tensile
Tester in accordance to ASTM D2256 Tensile properties of yarns by single strand method.
Procedure
a) Three burying areas 0.2m x 1.0m in size were carefully marked out and labelled Area
1, 2 and 3.
b) In each of the areas 10 strips (80mm x 200mm) of Vm1, Vm2 and Vm3 fabrics were
buried and watered according to the weekly watering schedule shown in Table 2.
c) After each week one fabric sample from each of the areas was collected and
unravelled into individual yarns and the tensile strength of five warp and five weft
yarns determined.
Gradient Erosion
The standard index test method (Figure 4) for the determination of unvegetated roll
erosion control product (RECP) ability to protect soil from rain splash and associated
runoff under bench-scale conditions [6] was adopted to determine erosion control
effectiveness of each fabric type at 1:1(11.3o), 2:1(14
o), 3.1(18.4
o), 4:1 (26.6
o) and
5:1.(45o) gradients. The collected "runoff sediment" was left to dry for a minimum of 24
hours, then weighed and the mass of eroded soil determined to ± 0.01 g.
Table 2 Weekly Watering Schedule
49
Figure 3 Average weather conditions in Bulawayo [10]
Results and Discussion
Determination of Cover Factor
Cover factor is defined as the number that indicates the extent to which the area of a fabric is
covered by one set of threads [12]. In this research cover factor refers to the ratio of soil loss
from a protected surface to soil loss from an unprotected surface. The RECP test result for the
cover factor provided by the fabrics Vm1, Vm2 and Vm3 were calculated by the formula;
Cover factor Vm = Soil loss from protected channel (MRECP) (1)
Soil loss from unprotected channel (Mcontrol)
Figure 4 Rainfall simulator [11]
50
Figure 5 shows the effect of gradient on the cover factor, Vm , for each fabric. The soil
erosion protection of the fabrics in order of increasing cover factors is as follows: Vm 3, Vm 2
then Vm 1 thus indicating the influence the aperture size has on the cover factor. The results
show that the cover factor is increasing with a decrease in the aperture size.
Figure 5 Effect of gradient on cover factor
This can be attributed to the fact that the fabric with a smaller aperture size has a greater
amount of cover due to the number of yarns per unit cross sectional area therefore, as the
aperture size decreases less soil particles can go through the fabric openings. Fabric Vm1
(10x10) is most effective at low and high gradients of inclination as it prevents a maximum of
82% soil loss, and a minimum of 56%.
For each geotextile, at slope inclinations 00 – 20
0, there is a steep increase in the cover factor
however, as the degree of inclination further increases the rate of increase in the cover factor
becomes smaller i.e. the geotextile becomes less effective. This can be attributed to an
increase in the gravitational pull acting on the soil particles as the degree of inclination is
increased thus resulting in more soil particles passing through the fabric openings.
Degradation of Sisal
An erosion control geotextile is temporary, as it provides erosion control until plants develop
to provide protection. The geotextile must therefore be degradable so as to allow for plant life
to take over. It was therefore important to find out how long the sisal geotextile takes to
degrade when subjected to weather elements.
The degradation period of the fabric was determined by using the experimental data obtained
over a period of 7 weeks. The line of best fit was derived from the data values of tenacity to
determine the point where the constituent yarns will have zero strength. The tenacity results
in Figure 6 show linear behaviour with a negative gradient indicating that the yarns were
continuously losing strength. After 7 weeks, the strength loss of the warp and weft yarns
51
dropped from 12.14 to 1.66 and 11.49 to 1.18 respectively. By using the line of best fit, the
expected point of degradation where the constituent yarns will have zero strength was
determined to be 7.8 weeks. This means that the fabric must be used with a plant that starts to
develop a steady root base within 8 weeks.
Figure 6 Weekly Tenacity of yarns
During the 8 weeks, the fabric might lose its structural stability as its strength reduces
however , the assumption is that before the complete deterioration of the fabric the plant will
also be helping with erosion control as the plant root formation occurs over a period of time
and it should be established before the sisal fabric completely biodegrades.
Conclusion
The effectiveness of an erosion control geotextile is its ability to provide temporary erosion
control until natural means such as root formation take over. The rate of degradation of
fabrics indicated by the continuous strength loss of the constituent yarns show that the sisal
fabrics will provide temporary cover until vegetation establishes necessary cover and
protection. Results also show that the slope gradient, and fabric structure (aperture size) play
a significant role in the rate of soil erosion.
References
[1] Ciubotariu A, Rusu L, Tiron C, Kovar R, Budulan C, Roman M (2010). Erosion
control using Geotextiles, 7th
International Conference TEXSCI 2010, September 6-8,
Liberec, Czech Republic.
[2] Wall G, Baldwin CS, Shelton IJ (1987). Soil Erosion – Causes and Effects,
Factsheet, http://www.omafra.gov.on.ca (15/10/2011 12:00pm)
[3] Morgan RPC (2005). Soil Erosion and Conservation Third Edition, National Soil
Resources Institute, Cranfield University.
52
[4] Vogel H (1992). Effects of conservation tillage on sheet erosion from sandy soils at
two experimental sites in Zimbabwe, Elsevier B. V, Netherlands, Applied Geography,
12,229-242.
[5] Pimentel D, Harvey C, Resosudarmo R, Sinclair K, Kurz D, McNair M, Crist S,
Shpritz L, Fitton L, Saffouri R, Blair R (1995). Environmental and Economic Costs of Soil
Erosion and Conservation Benefits, American Association for the Advancement of Science,
Science, New Seies, Vol 267.
[6] Wetland Rehabilitation Poster and Lesson Notes, http://www.waterwise.co.za
(09/10/2011).
[7] Joint Departments of the Army and Air Force (1995). Engineering Use of Geotextiles
TM 5-817-8/AFJMAN 32-1030.
[8] Practical Guide to Green Technology for Ground Engineering,
http://www.ismithers.net/downloads/chapters/ (15/10/2011).
[9] Smith R. The potential market for sisal and henequen geotextiles. http://www.fao.org
(02/01/2012 ).
[10] BBCWEATHER Bulawayo, http://www.bbc.co.uk/weather/894701.(09/02/2012).
[11] ECTC Test Protocol (2003). Standard Index Test Method for the Determination of
Unvegetated Rolled Erosion Control Product Ability to Protect Soil from Rain Splash and
Associated Runoff Under Bench-Scale Conditions, http://www.ectc.org (15/10/2011).
[12] Tubbs MC, Daniels PN (1991). Textile Terms and Definitions, Ninth Edition, The
Textile Institute, UK.
53
COMPRESSIVE STRENGTH EVALUATION OF BLENDED CEMENT
RICE HUSK ASH (RHA) CONCRETE Agbenyeku, E.E.
1) Okonta, F.N.
2)
1) & 2) Department of Civil Engineering Science, Faculty of Engineering and the Built
Environment,
University of Johannesburg, P. O. Box 524, Auckland Park 2006, South Africa 1)
E-mail: [email protected]
Key words: Rice Husk Ash, Pozzolanic properties, Cement, Compressive strength,
Agricultural Waste
Abstract
The cost saving benefits and potentials of using pozzolanas in cement production are well
documented in literature. Investigations on the use of artificial pozzolanas as Supplementary
Cementitious Materials (SCM) in concrete engineering are driven primarily by the need to
provide affordable and ecologically friendly home to the exploding global population. In the
continual search for substitute building/construction materials, the introduction of Rice Husk
Ash (RHA) as a cementitious material in concrete production was investigated. The
availability of this material provided the impetus for the study of the compressive strength of
concrete using RHA as a partial replacement for Ordinary Portland Cement
(OPC). Chemical analysis on RHA revealed the presence of significant quantities of active
pozzolanas. A total of 90 cubes of 150mm dimensions were cast with the percent cement
replacement by RHA ranging from 0 to 40%, while 28-day targeted strength of 25N/mm2 was
adopted as control. The cubes were cured at a relative humidity of 95 to100% and
temperature of 220
C to 250
C in a curing chamber for hydration periods of 7, 14, 21 and 28-
days. The results showed trends of strength development, revealing a decrease in the density
and compressive strength of samples with increase in RHA content. The 28-day density and
compressive strength of the normal concrete was 2465Kg/m3 and 28.57N/mm
2 while the
10%RHA sample (i.e. best replacement matrix) had 2398Kg/m3
and 25.97N/mm2
respectively.
The strength of 10%RHA/OPC concrete (25.97N/mm2) was higher than the adopted strength
(25N/mm2) at the 28-day, which makes it a suitable construction material. It can be a major
cost reduction factor in rural housing and development; where buildings of less structural
complexity are required. As such, it can be employed in the construction of simple
foundations and concrete composites.
INTRODUCTION
The development of supplementary cementitious materials (SCM) has become essential in
the advancement of low-cost construction materials used in the production of self-sufficient
means of shelter especially in developing countries. In recent past, the alarming and insistent
rise in the price of conventional construction/building materials has generated enormous
efforts from government, public and private sectors to search for locally available materials
as alternatives. These alternative materials are to supplement (i.e. partly or totally substitute)
the scarce and expensive conventional materials particularly in mortar and concrete
production. The use of these SCMs as admixtures not only improves concrete properties but
protects and conserves the environment by saving energy and natural resources [1]. Thus,
studies have been conducted to find the suitability of waste ash to replace cement in
conventional concrete [2-5]. Inert fillers in small amounts are acceptable as cement
replacement. Their pozzolanic properties convey not only technical advantages to the
resulting concrete but also enable larger quantities of cement to be successfully substituted
[6]. According to ECO-CARE [7], bulk of the cement used in construction work is the
54
Portland cement (PC) manufactured by mixing naturally occurring substances containing
calcium carbonate with substances containing alumina, silica and iron oxide. Over recent
decades, Portland cements (PC) containing Fly Ash (FA) and silica fume have gained
increasing acceptance while PC containing artificial pozzolans like sugar cane ash (baggase)
and burnt oil shale are commonly used in regions where they are abundant.
In pozzolanic materials, the amorphous silica present combines with lime and forms
cementitious materials. These materials can improve the durability of concrete, its rate of
strength gain and reduces the rate of liberation of heat of hydration which is highly beneficial
for mass concrete. Efforts are propelled toward substituting cement (wholly or partially) with
locally available pozzolanic materials like cassava peels ash, volcanic ash, saw dust ash,
millet husk ash, pulverized fuel ash, corn cob ash etc., in concrete [8,9]. This paper therefore
investigates the effect of merging locally available pozzolanic material Rice Husk Ash
(RHA) as partial replacement for cement on the strength characteristics of concrete [10]. The
addition of rice husk ash (a seemingly unsightly idle agricultural waste); into concrete is an
approach to transforming an agricultural waste material to an affordable and functional
produce. The 28-day strength is used as a trial assessment of pozzolanic activity in
consonance with ASTM C618 [11].
LITERATURE REVIEW According to Job [12], efforts have been made by researchers like Neville [13], Talero [14],
Popovics [15], and Smith [16] to practically substitute cement with locally available materials
called pozzolanas. “Pozzolana” is used to define naturally occurring and artificially siliceous
or siliceous and aluminous materials which in themselves have little or no cementitious
properties but in finely divided form and in the presence of moisture, chemically react with
calcium hydroxide which is liberated during the hydration of Portland cement at ordinary
temperatures to form compounds possessing cementitious properties [11, 17-20]. Research
trends on sourcing, discoveries, development and the use of alternative, locally available
materials have concentrated either on purely partial or total replacements of cement in
concrete revealing that pozzolanas can produce concrete with close characteristics as normal
concrete at age 28-days and beyond.
Rice which is a cereal grain, is the most important staple food for a large part of the world's
human population. It is the grain with the second-highest worldwide production, after maize
(corn). Ikpong [22], rice husk is the outer covering of the rice grain consisting of two
interlocking and it is an agricultural waste usually generated in large quantities during manual
or mechanical threshing process (figure-1). Neville and Brooks [17] and Verghese [23]
defined rice husk as a finely divided particle of agricultural waste measuring less than
11/2(i.e. about 1/9mm) in diameter, it is obtained when rice grain is removed from its shell.
Rice is normally grown as an annual plant around the world, although in tropical and sub-
tropical areas it can survive as a perennial and can produce a ratoon crop for up to 30 years.
This is a clear indication of its availability as an industrial raw material. Rice Husk Ash
(RHA) as shown in figure-3, is obtained after burning the husk in an electric furnace,
allowing accurate monitoring of the burning temperature maintained within the range of 650-
700oC in order to produce highly reactive amorphous ash [22]. Okpalla [10] described RHA
as a fine pozzolanic material, which by itself is poorly cementitious but in the presence of
lime and water forms a cementitious compound. The pozzolanic value of RHA depends on
the burning conditions and its colour is dependent on the carbon content of the ash.
Controlled incineration of the husk to about 7000C yields highly amorphous pozzolanic RHA.
According to Nagataki [21], the application of various ashes as potential cement substitutes
55
and replacements in mortar and concrete production has attracted the attention of researchers
as materials that not only contribute to improvement of concrete performance (i.e. increased
strength, durability and reduction of heat of hydration) but are also central to the reduction of
energy and carbon dioxide generated in the production of cement. Hence, researchers are
involved in experimental studies on various by-product mineral admixtures (i.e. waste ashes
and materials with pozzolanic potentials) such as; mining tailings, blast furnace slag,
pulverized fuel ash, volcanic ash, sawdust ash, wheat ash, sugar cane fiber (bagasse) ash, and
groundnut husk ash [8,15].
MATERIALS AND METHODS
Rice Husk used in this study was gotten as open dump waste from a local milling farm in
Lafia, Nassarawa State of Nigeria where at present, about 700 fully functional mills produce
rice for consumption. The rice shells (husk) were sun dried, burnt in open air and calcined in
an electric furnace to a temperature of about 700oC. The reactive amorphous rice husk
nodules (figure-2) were finely crushed and passed through the 75μm sieve. Results of the
RHA chemical content determined by X-Ray diffraction (XRD) and X-Ray fluorescent
(XRF) method shown in Table-1, reveals the total content of Silicon Dioxide (SiO2),
Aluminium Oxide (Al2O3) and Iron Oxide (Fe2O3) to be (75.87%) which is above the
minimum of 70% specified in ASTM C618 [11]. As such, indicates RHA (figure-3) to have
significant pozzolanic properties. RHA/OPC mix ratios ranging from 0 to 40% replacement
(produced in triplicates) were tested. The control specimen (i.e. plain concrete) was
proportioned for a targeted strength of 25N/mm2 in consonance with the British Mix Design
(D.O.E) method as the required minimum strength for structural concrete in accordance to
BS8110.
Table-1: Chemical composition of RHA (%)
Chemical
Composition
Fe2O3 SiO2 Al2O3 CaO
MgO
TiO
LOI
SiO2+Al2O3+Fe2O3
RHA 2.72 66.2 6.95 4.03 2.61 - 15.9 75.87
The mix proportion used for this study was 1:2:4. “Dangote”, locally produced ASTM Type I
Portland cement, conforming to the BS EN 197 [24] was used in this investigation. The
proportions of OPC/RHA in the concrete were 100:0% (as control), 90:10%, 80:20%,
70:30% and 60:40% respectively. The OPC/RHA substitution was computed by weight.
Physical properties from preliminary test results of the constituent materials are shown in
Table-2. The fine aggregate used was sharp river sand, free from impurities and injurious
substances while the coarse aggregate was 19 mm (3/4 inch) specific maximum size coarse
aggregate which were obtained from “Dantata and Sowoe Construction Company Nigeria
Limited, Abuja”. All the aggregates conformed to the British Standard Specification [25].
Portable tap water was used for the concrete mixing while the curing process was done in a
chamber.
56
Table-2: Summary of Physical Properties of Constituent Materials
Parameters RHA Sand Granite
Specific Gravity 2.97 2.55 2.63
Bulk Density (Kg/m3)
Uncompacted 1397 1375 1354
Compacted 1486 1428 1343
Void (%) 15.55 10.24 24.36
Moisture Content (%) 3.59
Sieve Analysis
Fineness Modulus (m2/Kg) 2.53
Coefficient of Uniformity (Cu) 8.05 1.43
Coefficient of Gradation (Cg) 1.04 0.95
Effect of the various percentage replacements of RHA on the compressive strength
properties (N/mm2) and demoulding densities (Kg/m
3) of RHA/OPC concrete were
investigated. For the comprehensive strength (N/mm2) to be determined, a total of 90
150(mm) dimension cubic samples were cast and cured at a relative humidity of 95 to 100
per cent and temperature of 220
C to 250
C in a curing chamber for hydration periods of 7,
14, 21 and 28 days. Permeable hessian bags were used to cover the samples and water was
constantly sprinkled on the cover over the seven day period up until the 28-day in
accordance with the TMH1 specifications [26]. At the end of every curing age, three
specimens (figure-4) of each mixture were crushed under direct loading using the
compression test machine and their averages were taken.
Table-3: Density (Kg/m3) and Compressive Strength (CS-N/mm
2) of RHA/OPC Concrete
Hydration Periods
OPC RHA
(%) (%)
7 14 21 28
Density CS Density CS Density CS Density CS
100 0 2435 18.07 2448 21.87 2479 24.98 2465 28.57
90 10 2429 15.85 2427 19.52 2399 23.76 2398 25.97
80 20 2397 13.46 2391 17.34 2384 20.47 2372 24.58
70 30 2279 10.04 2257 14.37 2236 18.14 2349 22.36
60 40 2248 7.86 2235 12.72 2232 16.05 2323 19.45
Figure-1. Rice Husk (disposed as waste) Figure-2. Rice Husk clinks
57
Figure-3. Incinerated RHA Figure-4. RHA/OPC Concrete Samples
RESULTS AND DISCUSSIONS Table-3 above shows the density (Kg/m
3) and compressive strength (N/mm
2) values of the
tested concrete samples. The result presented in Figure-5 show that; the percentage increase
in RHA, led to a decrease in the respective densities of RHA/OPC concrete.
Figure-5. Effect of RHA replacements (%) on Concrete Density (Kg/m3)
Figure-6. Compressive Strength (N/mm2) of respective concrete samples
At the 28-day hydration period, 0% RHA replacements (i.e. the control specimen), had a
density of 2465 Kg/m3; at 10% RHA replacements (i.e. the best replacement matrix), the
density was 2398 Kg/m3 indicating a loss of about 2.7% which can be as a result of the
difference in the fineness modulus of RHA with regard to cement, while their compressive
strength were gotten as 28.57(N/mm2) and 25.97(N/mm
2) respectively. The compressive
2050210021502200225023002350240024502500
0 10 20 30 40
DE
MO
UL
DIN
G
DE
NS
ITY
(K
g/m
3)
RHA REPLACEMENT (%)
7days R² = 0.88314days R² = 0.90921days R² = 0.91728days R² = 0.938
0
5
10
15
20
25
30
7 14 21 28
CO
MP
RE
SS
IVE
ST
RE
NG
TH
(N
/mm
2)
HYDRATION PERIOD (days)
0%RHA R² = 0.99810%RHA R² = 0.98520%RHA R² = 0.99730%RHA R² = 0.99940%RHA R² = 0.991
58
strength comparison between the control sample and the replacement matrices are shown in
figure-6.
There is a strong correlation between the compressive strength and the hydration period.
Although, the strength of cement blended with pozzolanas normally improves with age since
pozzolanas react more slowly than cement due to difference in composition but obtain similar
strength after about a year. However, the trend shows a gradual strength development of the
RHA/OPC concrete as the curing age increases. Hence, there is high tendency for this
concrete type to attain strength values similar to the control sample at prolonged hydration
periods.
Figure-7. Density of Concrete samples (Kg/m3) with respect to Curing Ages (days)
Figure-8. Effect of RHA replacement (%) on Compressive Strength (N/mm2) of concrete
Figure-7 reveals a drop in concrete density with increase in curing age. This can be accounted
for due to water absorption and the simultaneous loss in materials caused by the effect of
curing. However, the trend is not linear as the densities of specimens with higher contents of
RHA are seen to increase at 21-28days hydration periods. The increased densities
experienced by the specimens with higher percentage of RHA are associated with the
addition of RHA and the changes in the water absorption potentials of the mixes. As such,
there is a fairly strong correlation between the concrete density and the curing period. A
strong correlation is seen between the compressive strength of the samples and the percentage
RHA replacements. The progressive drop in the strength of samples with increase in RHA
over the different hydration periods as shown in Figure-8; can be accounted for as a result of
the excess amorphous silica and / or alumina from RHA not used up in the reaction. Hence,
2050210021502200225023002350240024502500
7 14 21 28
DE
MO
UL
DIN
G
DE
NS
ITY
(K
g/m
3)
HYDRATION PERIOD (days)
0%RHA R² = 0.65710%RHA R² = 0.83820%RHA R² = 0.97130%RHA R² = 0.24740%RHA R² = 0.446
0
5
10
15
20
25
30
0 10 20 30 40
CO
MP
RE
SS
IVE
ST
RE
NG
TH
(N
/mm
2)
RHA REPLACEMENT (%)
7days R² = 0.99414days R² = 0.99421days R² = 0.98628days R² = 0.988
59
the excess RHA simply contributed to the drop in strength. ASTM C618 for 28-day strength
therefore requires that the limit to which cement be replaced for quality and economy should
be 20% [11].
CONCLUSIONS
The results presented revealed that the 10%RHA replacement (i.e. the best
replacement matrix) had 28-day strength of (25.97N/mm2), which is less than the
control specimen (28.57N/mm2) but is above the targeted strength (25N/mm
2). Hence,
satisfies the minimum strength for structural concrete in accordance to BS8110;
The compressive strength of samples increases with increase in hydration period;
Water absorption and simultaneous loss in materials results in the reduction of density
of samples although, subsequent increase in density was observed for specimens with
high RHA content at a later period;
The introduction of RHA presents a good tendency of pozzolanic activity;
Over the hydration periods, significant drop in compressive strength of samples was
noticed in association with RHA quantities that were not utilized in the pozzolanic
reaction;
As such, this paper demonstrates how the use of appropriate technology can transform
abundantly available, cheap agricultural waste into a natural resource. Hence, the
RHA/OPC concrete can at the moment be utilized in the construction of simple
foundations and masonry walls; while further investigations are recommended to be
carried out for longer hydration periods of up to 120 days to ascertain the pozzolanic
tendencies, strength and durability of this new concrete type.
REFERENCES
[1] Elinwa, A.U. and Mahmood, Y.A., (2002). Ash from Timber Waste as Cement
Replacement Material, Cement and Concrete Composites, V. 24, No. 2, pp. 219-222.
[2] Al-Ani, M. Hughes, B., (1989). Pulverized-fuel ash and its uses in concrete, Mag. Concr.
Res.41 (147) pp. 55–63.
[3] Swamy, R.N., (1986). Cement Replacement Materials, Concrete Technology and Design,
Surrey University Press, Great Britain.
[4] Berry, E.E. Malhotra, V.M., (1980). Fly ash for use in concrete - a critical review, J. of
ACI 77 (8), pp. 59–73.
[5] Bilodeau, A. and Malhotra, V.M., (2000). High volume fly ash system: concrete solution
for sustainable development, ACI Mater. J, 99 (1), pp. 41–48.
[6] Khandaker M. and Anwar Hossain “Blended cement using volcanic ash and pumice”.
[7] ECO-CARE Education, (2005). Building Material: Composition of Ordinary Portland
Cement. http://www.ecocareeducation.com /building_material.htm
[8] Matawal, D.S., (2005). Application of Ashes as Pozzolana in Mortar and Concrete
Production, 1st National Academy Conference, 31st August - 2nd September
[9] Ujene, A.O. and Achuenu, E., (2005). The Compressive Strength of Concrete Containing
Varying Proportions Selected Locally Sourced Aggregates in Nigeria, International Journal
of Environmental Issues, Vol.3, No.1, pp. 81-87.
[10] Okpalla, D.C., (1987). Rice Husk Ash as a Partial Replacement for Cement in
Concrete, Proceedings of the Annual Conference of the Nigerian Society of Engineers, Port
Harcourt, Nigeria, pp. 1-12.
60
[11] American Society for Testing and Materials, Specification for Coal Fly Ash and Raw or
Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete,
ASTM C 618, 2008.
[12] Job, O.F., (1998). The Relationship between the Strength and Non-Destructive
Parameters of Pulverized Burnt Clay Concrete, Journal of Environmental Sciences
(JOES), Vol. 1, No. 2, pp. 9 (57 -64).
[13] Neville, A.M., (1992). Lime and Other Alternative Cements, U.K. International
Technology Publication.
[14] Talero, R., (1990). Qualitative Analysis of Natural Pozzolanas, Fly Ashes, and Blast
Furnace Slags by XRD, Journal of Materials in Civil Engineering 2(2), pp. 106-117.
[15] Popovics, S., (1998). What Do We Know about the Contribution of Fly Ash to the
Strength of Concrete, Proceedings of 2nd International Conference, ACI Special Publication
SP-91, Malhot. V.M. ed., Detroit. Mich, 1986, pp. 313 -332
[16] Smith, R., (1987) .Rice Husk Ash, Cement Progress in Development and Application
Report from India, Nepal and Pakistan
[17] Neville, A.M and Brooks J.J., (2002). Concrete Technology, 2nd
Edition, London,
Longman Publishers.
[18] Shetty, M.S., (2004). Concrete Technology – Theory and Practice, New Dhelhi, India, S.
Chand and Company Limited,
[19] Neville, A.M., (2006). Properties of Concrete, 4th Edition, copyright © 2000, Asia,
Person Education Pte. Ltd.
[20] Hassan, I.O., (2006). Strength Properties of Concrete obtained Using Volcanic Ash
Pozzolan as Partial Replacement of Cement, M.Sc. Thesis, Department of Building,
University of Jos.
[21] Nagataki, S., (1994). Mineral Admixtures in Concrete: State of the Art and Trends.
Special Publication, Materials Journal 144: 447-482.
[22] Ikpong, A.A., (1993). The relationship between the strength and Non destructive
parameters of Rice husk ash concrete, cement and concrete Research 23, pg, 387-398
London: cement and concrete Association.
[23] Varghese P.C., (2006). Building Materials, New Delhi, Prentice – Hall of India.
[24] British Standard Institution, Cement- Composition, Specifications and Conformity
Criteria for Common Cements, BS EN 197: Part 1, London.
[25] British Standard Institution, Method for Determination of Particle Size Distribution, BS
812: Part 103, 1985, London.
[26] TMH1. 1986. Standard Methods of Testing Road Construction Material, Technical
Methods for Highways. Vol. l1.