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J. Civil Eng. Architect. Res Vol. 4, No. 4, 2017, pp. 2003-2010 Received: May 31, 2017, Published: April 25, 2017
Journal of Civil Engineering
and Architecture Research
Improving Durability of Compressed Earth Blocks in Low-Cost Housing Construction Using Sap from Cactus Plant
Ivan Agaba, Lawrence Muhwezi and Sam Bulolo
Department of Civil and Building Engineering, Kyambogo University, Kampala, Uganda
Corresponding author: Lawrence Muhwezi (lmuhwezi@hotmail.com)
Abstract: Adequate shelter is a basic human need and yet about 80% of the urban population in developing countries Uganda inclusive still lives in spontaneous settlements as they cannot afford the high cost of building materials. CSBs (compressed stabilized blocks) have been identified as a low-cost material with the potential to address the problem and reverse the shelter backlog in Uganda. While their other properties are well understood, their durability remains unknown. This research, therefore, investigated the viability in the use of cactus sap to improve the durability of CSB’s, as alternative building materials in Uganda. The sap sample was extracted from prickly pear cactus plant and applied on CSB surfaces obtained from a local producer. Laboratory abrasion test, water absorption and mechanical strength of the earth blocks were conducted. Comparison of the properties of traditional earth blocks (control samples) and other blocks improved by either cactus sap only or a combination of cactus sap with lime was carried out. It was established that the latter exhibited abrasion coefficient and wet compressive strength of 147 mm2/g and 1.53 N/mm2 while the former, 219 mm2/g and 1.90 N/mm2 respectively which were higher than 118 mm2/g and 1.27 N/mm2 for the traditional blocks. It was concluded that cactus could be used as a protective cover material on earth block surfaces hence improving their durability when used as external walling units. The findings of this study will contribute to the widespread use of CSB’s in low cost housing construction since prospective users can now be confident about their durability under wet conditions. Further research is recommended to explore the performance of CBSs when a combination of cactus mucilage with lime when the percentages of lime are varied to obtain the optimum amount of lime needed.
Keywords: Durability, strength, cement-soil stabilized blocks and cactus.
Abbreviations
CSBs Compressed Stabilised Blocks
ILO International Labour Organisation
UNIDO United Nations Industrial Development Organisation
UNCHS United Nations Centre for Human Settlements
WCS Wet Compressive Strength
TWA Total Water Absorption
BBD Block Dry Density
BRE Building Research Establishment
1. Introduction
Adequate shelter is one of the most important basic
human needs, yet 25% of the world’s population does
not have any fixed abode, while 50% of the urban
population lives in slums [1, 2]. Indeed 80% of urban
settlements in developing countries consist of slums
and spontaneous settlements made of temporary
materials [3, 4].
With the population in developing countries
growing at rates of between 2% and 4% per year and
the population in their major cities growing by double
these figures, demand for low cost housing far
outstrips the capacity to supply [5]. No developing
country without strategies for low cost materials is
likely to meet its shelter targets [6, 7].
Improving Durability of Compressed Earth Blocks in Low-Cost Housing Construction Using Sap from Cactus Plant
2004
Developing countries planning to expand their
housing stock for the low-income groups will
inevitably need to identify the lowest feasible unit
housing costs. The main costs of shelter provision are
for building materials (about 60%), machinery,
manpower and loan interest repayments [8-10].
Strategies are therefore urgently needed to develop
low-cost, readily available and durable building
materials. A naturally abundant material such as soil
that is found on most of the surface of the earth should
be a significant resource for building in developing
countries.
1.1 Advantages of Using CSBs
The use of CSBs will continue to grow due to the
several merits and economics associated with its use.
Firstly, as the basic raw material is soil, its source will
remain abundant and this facilitates direct
site-to-service application, thereby lowering costs
normally associated with acquisition, transportation
and production. House construction and ownership
can therefore be achieved at comparatively low costs.
Secondly, the initial performance characteristics of the
material such as the WCS (wet compressive strength),
dimensional stability, TWA (total water absorption),
BDD (block dry density) and durability are technically
acceptable. They are also comparable to those of rival
materials [2, 11, 12]. Thirdly, promoting the use of
CSBs generates more direct and indirect employment
opportunities within the local populace than would be
the case with other materials. Fourthly, use of the
material contributes directly to the social, cultural and
educational advancement of the population [13-15].
Their use also contributes to the training and
re-training of artisans and to the provision of new
skills. Use of the material through the provision of
local infrastructure such as schools, community
centres, health centres and administrative units results
in the promotion of human interactions and social
development. Finally, use of the material is
environmentally friendly, appropriate and correct
since it utilises the otherwise unlimited natural
resource in its natural state.
Moreover, this is achieved with little resultant
depletion of other resources, or pollution and requires
no excessive energy consumption and wastage as is
the case with clamp fired bricks. The elimination of
the need for wood fuel resources is seen as a major
attraction over such bricks. The use of CSBs is thus in
keeping with current sustainable development
strategies [16-20].
1.2 Shortfalls of Using CSBs
Despite the above advantages however, as with
most relatively new materials, shortcomings
associated with their use have recently begun to
emerge, especially in tropical environments. These
regions are characterized by frequent and intense
rainfall, high relative humidity and high diurnal
temperature changes [21-23]. CSBs are produced from
soil as the bulk constituent (over 90%). Soil is known
to have poor resistance to erosion and to disintegration
in water, a low tensile strength, low resistance to
abrasion, high water absorption and retention capacity,
and is dimensionally unstable during cyclic wetting
and drying [24-26]. The vulnerability of soil has in
turn led to blocks showing considerable defects over
short periods under conditions of normal and severe
exposure in the humid tropics [27-31].
Defects in CSB structures are mainly presented as
surface erosion, volume reduction, cracking and
crazing, surface pitting and roughening and
detachment of render. These deterioration phenomena
have been predominantly witnessed in the wet humid
tropical regions of the world. Whereas the initial
building costs might be low, the subsequent high
maintenance costs, or even early rebuilding costs are
not affordable by many. Some promoters have also
done harm to the image of the material by claiming a
high degree of long-term technical performance only
to be contradicted by premature deterioration only a
few years later. The most significant part of the
Improving Durability of Compressed Earth Blocks in Low-Cost Housing Construction Using Sap from Cactus Plant
2005
physical structure is the walling constituents, which is
about 60% [32]. Thus, it makes greater sense to
concentrate work on low-cost walling. Dwelling cost
can be split into a number of separate areas.
Although the problem is more acute in the humid
tropics than in the arid zone, it nevertheless has not
been seriously addressed by research. Interest in
studying the durability of CSBs is therefore likely to
remain a major research concern for the foreseeable
future. It is the long-term durability of the block,
rather than any other factor that will be the key to their
widespread acceptance [33]. It was therefore the aim
of this research to investigate the viability of using
cactus sap as a waterproofing material that can
withstand severe exposure conditions of wetting,
abrasion and drying.
2. Materials and Methods
Soil, cement and cactus sap were the raw materials
that were used for this study (Table 1). Earth or soil,
considered suitable for manufacturing compressed
earth blocks was taken from Kyambogo University
compound in Kampala. HIMA cement, was the
cement used and cactus mucilage required for
stabilisation of the blocks was harvested from cactus
plants near Nabisunsa Secondary school in the
neigbourhood of Kyambogo University. The other
material used to moist the above stated materials was
tap water.
Twenty one blocks in total were delivered at
COMATLAB, a private material testing company and
different tests: abrasion test, water absorption
properties of the blocks and the mechanical strength of
the earth blocks were conducted. The research
examined the interplay between constituent materials
used (cement, soil, water) in production of blocks and
the block surface characteristics with regard to
abrasion resistance and water absorption after
applying prickly pear cactus. Through literature
review, the characteristics of sap, its extraction
process from cactus, and the current methods used to
Table 1 Raw materials for sample preparation
Material Type Effect Process
Prickly
pear cactusCactus
Water
proofing Physical-chemical
Portland
cement Mineral Cementation Chemical
Soil Sandy-clayey
material Compaction Mechanical
select the main constituent materials in CSB’s were
reviewed.
2.1 Cactus Sap Harvesting
All production operations were carried out
manually with simple harvesting tools (Fig. 1): knife,
tongs, basin or bucket and gloves. Cactus pads were
cut into smaller pieces that can be easily cut further by
the grater. The sap sample was collected and stored in
a bucket.
2.2 Soil Preparation
The soil sample that was used to produce CSBs was
obtained from Kyambogo University which was
predominantly clay, sandy soil was then purchased to
be mixed with it in propotions of 75% with 25% of the
sample already had, to form the soil of the desired
design properties.
2.3 Sap Extraction Process (Fig. 2)
The following procedure was followed to extract
the sap:
Cactus pads were harvested and cut into very small
Fig. 1 Harvesting of the cactus pads.
Improving Durability of Compressed Earth Blocks in Low-Cost Housing Construction Using Sap from Cactus Plant
2006
pieces using a grater. The volume of cut cactus pads
filled aquater of the bucket volume. Water was added
in a proportion of 3 times the volume of chopped
cactus. The mix was left in the bucket in a storeroom
for three days, covered to limit evaporation. This mix
was less viscious than the one left after two days.
The blocks were first sprayed with water using a
pipe. Using a painting brush, the cactus sap was
applied on the block surfaces in three layers, applying
each layer a day (Fig. 3). One block was not painted
with the sap and both categories were left in an open
place (humid conditions) for a week. After two weeks
visual evidence showed that the block surface without
cactus was being eroded. A combination of cactus sap
and lime was similarly applied on surfaces of other
sample blocks using the same procedure.
During this research three categories of blocks were
investigated namely:
Earth blocks without anything;
Earth blocks with cactus only;
Earth blocks with cactus mixed with lime.
Fig. 2 Removing the spines from the cactus pad Application of cactus sap on blocks.
Fig. 3 Process of applying cactus sap on the blocks.
3. Laboratory Tests and Findings
3.1 Dry Compressive Strenth Test
The method adopted for this experimented is well
detailed in BS 1881, Part 116: 1983. The dimensions
of each block were first taken using a measuring tape
and afterwards, they were weighed (Fig. 4). Blocks
were then placed under two plates of the crushing
machine. At the point of failure, the machine
automatically calculated the compressive strength and
the value was displayed on its monitor (Fig. 5). The
averages of the three block categories were each
calculated.
3.2 Abrasion Strength Test
The procedure adopted is described in Ref. [34]. A
CSB was subjected to mechanical erosion applied by
brushing with a metal brush at a constant pressure
over a given number of cycles. The brushing was
applied to the sides of the block which are actually
used as facing, i.e. usually the header or the stretcher.
Fig. 4 Taking readings of the block weights.
Fig. 5 Crushing machine.
Improving Durability of Compressed Earth Blocks in Low-Cost Housing Construction Using Sap from Cactus Plant
2007
The abrasion coefficient can then be calculated as the
ratio of the brushed surface area to the quantity of the
material removed by brushing and is proportional to
the abrasive strength. The brushed surface area was
calculated
(1)
where L = length of the brushed face of the block, W =
width of the brush.
The Abrasion Coefficient,
Ca = [S/(Ml - M2)] (2)
where M1 is mass of block before brushing and M2 is
mass of block after brushing.
3.3 Water Absorption Test
The TWA (Total Water Absorption) was calculated
by taking the amount of water absorbed by a dried
sample that had been immersed in water for a
specified period of time (24 hours). Mean values
obtained were taken as the TWA of the sample. The
result was expressed as a percentage of the original
dry mass of the specimen to the nearest 0.1% of the
dry mass. The method adopted for this experimented
is well detailed in Ref. [35].
The dimensions of each block were first taken and
then placed an oven for 24 hours. Blocks were fully
immersed in a water bath, and left there for 24 hours.
Blocks were removed from the water bath after 24
hours and wiped. The water absoption was then
determined using Eq. (3).
Water absorption = [(Mw – Md)/Md *100] % (3)
where Mw (g) is mass of wet blocks, Md (g) is mass of
blocks after drying.
4. Results and Discussion
4.1 Compressive Strength
The results of dry compressive strength of CEBs
from the laboratory are shown in Table 2. These
values fall within the permissible compressive strength
of earth building elements which are between 3 and 5
N/mm2 [36] and Ref. [37] provides results of between
2 and 7 N/mm2. Therefore, the tested blocks can be
used as building units.
The results and findings from the laboratory
experiments which compared the properties of
traditional blocks (control sample) and blocks
improved by either cactus mucilage only or a
combination of cactus mucilage with lime, established
that all the three block categories indicated a dry
compressive strength slightly above 3 N/mm2. The
latter indicated abrasion coefficients of 147 mm2/g,
219 mm2/g and wet compressive strengths of 1.53
N/mm2, 1.90 N/mm2 respectively which are higher
than 118 mm2/g and 1.27 N/mm2 for the traditional
blocks.
4.2 Wet Compressive Strength
It has been recommended in earlier studies that the
ratio of the mean dry and wet compressive strength in
CSB’s should not be greater than 2 [12]. The ratios for
the tested blocks were 0.47, 0.62, 0.39 for earth blocks
with cactus only, cactus with lime and those without
anything added respectively. The results obtained as
indicated in Fig. 6 are therefore within the
recommended limits.
The difference in strength can be explained by the
fact that the blocks without anything added to their
surface absorbed more water and the presence of more
moisture in these blocks lowers the weak van der
Waals bonds between the surfaces of the cement
hydrates and the surface of the sand particles in the
material more than the other two categories.
The moisture state of a block can influence its
strength. Saturated blocks are weaker than dry blocks
[12, 33]. The difference in strength can be explained
in a number of ways. Firstly, the presence of moisture
in a block lowers the weak van der Waals bonds
Table 2 Dry compressive strength of different blocks.
Block identity Dry compressive
strength (N/mm2)
Earth blocks with Cactus only 3.25
Earth blocks with Cactus and lime 3.06
Earth blocks without anything added 3.29
2008
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under various
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Fu
of the c
the per
amoun
Refer
[1] BuPaSyLo
[2] SmIn
[3] J. CoSc
[4] SmOr
[5] CoN(H
[6] DPrHPa
[7] NFlPu
[8] BuBuM
[9] ALo
[10] J.H4t
[11] HCoTe
[12] HBlSe
[13] E.EcLo
n Low-Cost HoPlant
ince there ar
gation should
ut if they all h
ude on which o
ms of durability
urther researc
combination o
rcentages of li
nt of lime need
rences
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