partial replacement of cement with sewage sludge
TRANSCRIPT
PARTIAL REPLACEMENT OF CEMENT WITH SEWAGE SLUDGE ASH (SSA) IN
MORTAR
WONG YIH KANG
Thesis submitted in fulfilment of the requirements
for the award of the degree of
B.Eng (Hons.) Civil Engineering
Faculty of Civil Engineering and Earth Resources
UNIVERSITI MALAYSIA PAHANG
JUNE 2015
vi
ABSTRACT
One of the methods of sewage sludge disposal is incineration. Although the incineration
process is able to reduce the volume of the sewage sludge, it is not a proper solution
since the ash generated after the incineration process must be disposed to landfill. The
aim of this research is to study the partial replacement of cement with sewage sludge
ash, SSA in mortar through experimental works. The experimental works were carried
out to access the feasibility of utilizing SSA as a construction material. An attempt has
been made to replace 10% and 15% of the mass of cement with 600°C and 800°C
incinerated SSA into the mortar. In this research, the sewage sludge is acquired from
Indah Water Konsortium (IWK), sewage treatment plant in Kuantan, Pahang. The
compressive strength and total porosity test were conducted by using 50 mm x 50 mm x
50 mm mortar cubes at the ages of 1, 7, 28 and 90 days. X-ray Diffraction (XRD), X-
ray Florescence (XRF) and Field Emission Scanning Electronic Microscope (FESEM)
were carried out to determine the chemical composition and the microstructure of the
sewage sludge, SSA and SSA mortar. The result of the compressive strength test shows
that the mortar with 10% replacement of 800°C burnt SSA increase in compressive
strength up to 1.14% and 5.06% at the ages of 28 days and 90 days, respectively. The
total porosity of the mortar also decreases up to 7.05% after the replacement of 10%
800°C burnt SSA after 90 days. The XRD and XRF tests show that the major
components in sewage sludge are SiO2, Al2O3 and Fe2O3. The incineration process
triggered the formation of those oxides in SSA where SiO2, Al2O3 and Fe2O3 can act as
pozzolan in cementatious materials. The particles of SSA are discrete spherical particle
and have wide range of sizes i.e. from 3.5 μm to 35 μm. The formation of needle shape
particles can be observed from the FESEM micrograph of SSA mortar which indicates
the pozzolanic activities of SSA.
vii
ABSTRAK
Salah satu kaedah pelupusan enapcemar adalah pembakaran. Walaupun proses
pembakaran dapat mengurangkan isi padu enapcemar, tapi pembakaran bukan
penyelesaian yang betul kerana abu yang dihasilkan selepas proses pembakaran perlu
dilupuskan ke tapak pelupusan. Tujuan kajian ini adalah untuk mengkaji gantian separa
simen dengan abu enapcemar, SSA dalam mortar melalui kerja-kerja eksperimen.
Kerja-kerja eksperimen telah dijalankan untuk mengantikan SSA sebagai bahan
pembinaan. Satu percubaan telah dibuat untuk menggantikan 10% dan 15% daripada
jisim simen dengan 600°C dan 800°C SSA dalam mortar. Dalam kajian ini, enapcemar
adalah diperolehi daripada Indah Water Konsortium (IWK), loji rawatan kumbahan di
Kuantan, Pahang. Ujian mampatan dan ujian keliangan telah dijalankan dengan
menggunakan 50 mm x 50 mm x 50 mm mortar kiub pada umur 1, 7, 28 dan 90 hari. X-
ray Diffraction (XRD), X-ray Florescence (XRF) dan Field Emission Scanning
Electronic Microscope (FESEM) telah dijalankan untuk menentukan komposisi kimia
dan mikrostruktur enapcemar, SSA dan SSA mortar. Keputusan ujian mampatan
menunjukkan bahawa mortar dengan penggantian 10% SSA yang dibakar pada 800°C
meningkatkan kekuatan mampatan sebanyak 1.14% dan 5.06% pada umur 28 hari dan
90 hari. Jumlah keliangan mortar juga menurun kepada 7.05% selepas penggantian 10%
800°C bakar SSA selepas 90 hari. Ujian XRD dan XRF menunjukkan bahawa
komponen utama dalam enapcemar adalah SiO2, Al2O3 dan Fe2O3. Proses pembakaran
dapat mencetuskan pembentukan SiO2, Al2O3 dan Fe2O3 dalam SSA. SiO2, Al2O3 dan
Fe2O3 boleh bertindak sebagai pozolan dalam bahan cementatious. Zarah SSA adalah
zarah sfera diskret dan mempunyai pelbagai saiz dalam 3.5 μm ke 35 μm. Pembentukan
zarah bentuk jarum boleh diperhati daripada mikrograf FESEM dalam SSA mortar,
pembentukan zarah bentuk jaram menunjukkan aktiviti pozzolanic SSA dalam mortar.
viii
TABLE OF CONTENTS
Page
SUPERVISOR’S DECLARATION ii
STUDENT’S DECLARATION iii
ACKNOWLEDGEMENTS v
ABSTRACT vi
ABSTRAK vii
TABLE OF CONTENTS viii
LIST OF TABLES xi
LIST OF FIGURES xii
LIST OF SYMBOLS xiv
LIST OF ABBREVIATIONS xvi
CHAPTER 1 INTRODUCTION
1.1 Background 1
1.2 Problem Statement 3
1.3 Objective 4
1.4 Scope of Study 4
1.5 Research Significance 4
1.6 Expected Outcome 6
CHAPTER 2 LITERATURE REVIEW
2.1 Introduction 7
2.2 Natural By-Product as Cement Replacement Material 7
2.3 Mortar 9
2.4 By-Product From Municipal Waste 10
2.4.1 Utilization of Sewage Sludge for Agricultural
Purpose
11
2.4.2 Utilization of Sewage Sludge as Building Block 12
ix
2.5 Sewage Sludge Ash 13
2.5.1 X-ray Diffraction (XRD) Test on SSA 15
2.5.2 X-ray Florescence (XRF) Test on SSA 18
2.5.3 Field Emission Scanning Electronic Microscope
(FESEM) Test on SSA
20
2.5.4 Pozzolanic Activity in SSA 22
2.5.5 Effect of Burning Temperature on SSA 24
2.5.6 Effect of Replacement Percentages 26
2.5.7 Correlation Between Compressive Strength and
Total Porosity
28
2.6 Summary 28
CHAPTER 3 RESEARCH METHODOLOGY
3.1 Introduction 30
3.2 Material of Mortar Paste 31
3.2.1 Sewage Sludge Ash 31
3.2.2 Cement 35
3.2.3 Fine Aggregate 36
3.2.4 Water 37
3.3 Preparation of Mortar Mix 37
3.4 Test Procedures 41
3.4.1 Compressive Strength Test 41
3.4.2 Total Porosity Test 44
3.4.3 X-ray Diffraction (XRD) 45
3.4.4 X-ray Florescence (XRF) 46
3.4.5 Field Emission Scanning Electronic Microscope
(FESEM)
47
CHAPTER 4 RESULT AND DISCUSSION
4.1 Introduction 49
4.2 Hardened Properties Results of SSA Mortars 49
4.2.1 Compressive Strength 50
4.2.2 Total Porosity 54
4.3 Correlation of Compressive Strength and Total Porosity 56
4.4 Chemical Composition Results 58
4.4.1 X-ray Diffraction (XRD) 59
4.4.2 X-ray Florescence (XRF) 62
4.4.3 Field Emission Scanning Electronic Microscope
(FESEM)
67
x
4.5 Optimal Percentages of Replacement and Burning Temperature
of Sewage Sludge Ash
74
4.6 Summary 75
CHAPTER 5 CONCLUSION AND RECOMMENDATION
5.1 Introduction 77
5.2 Conclusion 77
5.3 Recommendation for Future Research 79
REFERENCES 80
APPENDICES
A Result for Compressive Strength Test 84
B Result for Total Porosity Test 89
C Photos of Laboratory Preparation 94
xi
LIST OF TABLES
Table No. Title Page
2.1 Type of sewage sludge and its characterization 10
2.2 Content of heavy metal 14
2.3 Result of XRF Analysis 19
2.4 Chemical composition of OPC and sewage sludge ash 24
3.1 Compositions of Mortar Mixture 39
3.2 Name representation of mortar cube samples 39
4.1 Name representation of mortar cube samples 51
4.2 Summary of cube compressive strength result 51
4.3 Summary of cube total porosity result 54
4.4 XRF test for element in sewage sludge, 600°C SSA and 800°C
SSA
65
4.5 XRF test for oxide in sewage sludge, 600°C SSA and 800°C
SSA
67
4.6 Yielding of 600°C and 800°C burnt SSA 76
xii
LIST OF FIGURES
Figure No. Title Page
2.1 XRD pattern of sewage sludge ash at different sintered
temperature
17
2.2 SEM micrographs of cement with replacement of sewage sludge
ash for (a) 0%, (b) 2.5% (c) 5% (d) 10% (e) 15%
22
2.3 SEM micrographs of sewage sludge ash in different temperature
of incineration
23
3.1 Flow chart showing the preparation of material and test 32
3.2 Sewage sludge 33
3.3 Furnace 34
3.4 Furnace and sewage sludge samples in crucibles 34
3.5 600°C burnt sewage sludge ash 35
3.6 800°C burnt sewage sludge ash 35
3.7 Sieve shaker with 150 μm sieve 36
3.8 YTL ORANG KUAT Ordinary Portland Cement 37
3.9 Natural fine aggregate 37
3.10 Electronic balance 38
3.11 50 mm x 50 mm x 50 mm engineering steel mould. 39
3.12 Mortar mixer 40
3.13 The mortar paste in steel mould 40
3.14 Vibrating table 41
3.15 Water curing tank 41
3.16 Compressive strength machine 42
3.17 Metal Vernier Caliper 43
3.18 Compressive strength machine during testing 44
3.19 Maximum load and maximum strength 44
3.20 Vacuum saturation apparatus 45
3.21 Vacuum saturation apparatus during testing 45
3.22 Samples prepared for XRD test 47
3.23 X-ray Diffraction machine (XRD) 47
3.24 Bruker S8 Tiger XRF spectrometer 48
xiii
3.25 Sputter coater 48
3.26 FESEM JEOL JSM-7800F 49
4.1 Compressive strength against curing time graph 53
4.2 Total porosity against curing time graph 56
4.3 Correlation between compressive strength and total porosity for
0 SSA
58
4.4 Correlation between compressive strength and total porosity for
A10 SSA
58
4.5 Correlation between compressive strength and total porosity for
B10 SSA
58
4.6 Correlation between compressive strength and total porosity for
A15 SSA
59
4.7 Correlation between compressive strength and total porosity for
B15 SSA
59
4.8 XRD pattern of raw sewage sludge 61
4.9 XRD pattern of 600°C sewage sludge ash, SSA 62
4.10 XRD pattern of 800°C sewage sludge ash, SSA 63
4.11 FESEM image of raw sewage sludge at (a) 200 x (b) 1 kx (c) 3
kx (d) 5 kx (e) 10 kx
68
4.12 FESEM image of sewage sludge ash burnt at 600°C at (a) 200 x
(b) 1 kx (c) 3 kx (d) 5 kx (e) 10 kx
69
4.13 FESEM image of sewage sludge ash burnt at 800°C at (a) 200 x
(b) 1 kx (c) 3 kx (d) 5 kx (e) 10 kx
70
4.14 FESEM image of 0 SSA control mortar at (a) 200 x (b) 1 kx (c) 3
kx (d) 5 kx (e) 10 kx
71
4.15 FESEM image of A10 SSA mortar at (a) 200 x (b) 1 kx (c) 3 kx
(d) 5 kx (e) 10 kx
72
4.16 FESEM image of B10 SSA mortar at (a) 200 x (b) 1 kx (c) 3 kx
(d) 5 kx (e) 10 kx
73
4.17 FESEM image of B15 SSA mortar at (a) 200 x (b) 1 kx (c) 3 kx
(d) 5 kx (e) 10 kx
74
(d)
xiv
LIST OF SYMBOLS
% Percent
mm Millimetre
mm2
Millimetre square
m3
Cubic metre
μm Micro metre
g Gram
kg Kilogram
kg/m3 Kilogram per cubic metre
N/mm2 Newton per square millimetre
kN Kilo newton
°C Degree Celsius
° Degree
kN/sec Kilo newton per second
P Total porosity
WSA Weight of saturated samples measured in the air
WSW Weight of saturated samples measured in water
Wd Weight of oven dry samples measured in the air
θ Theta
R2 Correlation coefficient
cps Count per second
ppm parts per million
xv
x Times
kx Thousand times
xvi
LIST OF ABBREVIATIONS
ASTM American Society for Testing and Materials
BS British Standard
MS Malaysian Standards
IWK Indah Water Konsortium
SSA Sewage Sludge Ash
SDA
Sawdust Ash
CEM Certified Energy Manager
i.e. That is
e.g. For example
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND
Sewage sludge is a waste or by-product that generated during process of
purification of domestic and industrial waste water. As the population increases
drastically every year, the generation of sewage sludge waste in Malaysia has been
rapidly increasing. Malaysia produces 3.2 million cubic metres of domestic sludge
every year and increases to 4.3 million cubic metres by the year of 2005. Indah Water
Konsortium Sdn Bhd (2010) recorded that an estimation of 7 million cubic metres of
sewage sludge will be produced annually in the year of 2020. Although there are
methods to consolidate, stabilize and dewater the sewage sludge, but most of the sludge
is ended up to be disposed by landfill even after treated. Landfill has become dominant
manner of sewage sludge waste. However, landfill is only a temporary solution for the
disposal of sewage sludge waste because there is limited space for the sludge waste to
be disposed. The waste sewage sludge generated from the sewage treatment plant
consists of organic and inorganic matters. Rizzardini & Goi (2014) stated that the
disposal of waste sludge by landfill has become a serious threat to the environment due
to the toxic content of sewage waste in Italy. The untreated sewage sludge has caused
serious pollution to the soil condition. In Malaysia, the pollution caused by the disposal
of sewage sludge cannot be ignored and needs immediate remedial.
As the problem triggered by landfill become worst, awareness from the public
and government has been raised upon this problem. To encounter the problem, there are
researchers studied the properties of sewage sludge so that it can be reused. The wasted
sewage sludge can be utilized as resources after treatment process. For example, treated
2
and stabilised sewage sludge can be utilised for soil conditioning. Treated sludge is inert
and stable where it might be suitable for agriculture use. The sewage sludge consists of
chemical composition of phosphorus, nitrogen and organic matters which has fertilizer
properties. These components in sewage sludge are proved for the ability to improve the
condition of agriculture soil. However, Lin et al. (2012) concluded that sewage sludge
consist more than 5% content of heavy metal which shows that sewage sludge has high
amount of heavy metal. The content of heavy metal might be harmful for human
consumption. Donatello & Cheeseman (2013) stated that there are also limitations to the
application because sewage sludge contains heavy metal that may contaminate
agriculture soil. Public also consider the risk of pathogen from sewage sludge
transferred to the crops. Application of sewage sludge for agriculture has become even
difficult as fertilizer quality is standardized.
However, the utilization of sewage sludge for agriculture use is not the only way
to reduce the amount of sewage sludge waste. Researches have been carried out on
sewage sludge so that the waste sewage sludge can be applied in construction field. The
research is including the study of the chemical composition in sewage sludge after the
incineration process and the suitability of sewage sludge to be utilized as construction
materials. Sewage sludge ash consists of huge amount of silicate oxide, aluminium
oxide and iron oxide after the incineration process as has been proven (Jamshidi et al.,
2010). Silicate oxide, aluminium oxide and iron oxide can react with the product from
the cement hydration process and provide additional strength to the cementatious
material. Due to this property, SSA becomes a refined pozzolan that can trigger the
pozzolanic activity in cement based material. In the study of chemical engineering
(Tantawy et al., 2012), the pozzolanic activity is able to enhance the strength
development at the later stage of curing. Besides, the particle size of SSA is relatively
small after the incineration process where it can fills the pores and voids inside the
cement based materials and reduce its porosity. The enhanced cement paste with SSA
has higher durability and life span. The incinerated sewage sludge ash is potentially
reused to produce mortar, concrete, brick and pavement with partial replacement
sewage sludge to the cement. In this research an attempt is made on the partial
replacement of cement with sewage sludge ash into mortar.
3
1.2 PROBLEM STATEMENT
Sewage sludge waste has become one of the largest scale solid wastes at
Malaysia. Nowadays, the large amount of waste produced by water treatment plant has
overloaded the landfill, not to mention other waste from different sources. Malaysia is
currently facing the solid waste management problem. The collection and disposal cost
of municipal waste has become a burden to government and people. It is rather
extravagant to spend on the handling, transportation, and collection of sewage sludge.
Idrus (2008) stated that Malaysia has limited landfill site. Every day, each
person produces about 1 kg of solid waste and the waste production rate is increasing at
15% per year due to the urbanization and population growth. The disposal rate of
municipal waste is far higher than the decomposition rate at landfill. In a very short
period, the current landfill in Malaysia will reach their design capacity. Although the
volume of sludge is reduced after the incineration process, the sewage sludge ash from
the incineration process must be disposed. In the meantime, Malaysia has limited
research about the properties and characteristic of sewage sludge. There are plenty of
researches conducted in foreign country to apply sewage sludge ash as construction
materials and some of the researches show positive results. The chemical compositions
of sewage sludge consist of various types of heavy metal and minerals that may cause
harm to human and environment.
Malaysia is one of the world’s most resources-rich countries and has very fast-
growing economy. The development of construction industry has been marked as the
main catalyst to attain the status. During the transformation to become a developed
nation, the process of urbanization consumes a large amount of natural resources.
Cement is one of the major materials used in construction and the production of cement
consumes a lot of energy. Benhelal et al. (2013) stated that cement industry is one of the
largest carbon dioxide, CO2 gas emission sources, approximately 5% to 7% of global
CO2 emission are from the cement plants. CO2 may cause greenhouse effect and global
warming which may greatly influence the temperature of the earth. Apart from that, the
production of cement consumes a lot of energy where the lime is incinerated up to
1100°C.
4
1.3 OBJECTIVE
The main objective of this research is to study the chemical properties and
hardened properties of mortar with partial replacement of SSA to the mass of cement.
1. To identify the chemical properties of pure SSA and burnt SSA.
2. To determine the mechanical properties of SSA mortar, i.e. compressive strength
and total porosity.
3. To determine the optimal percentage of replacement of SSA.
4. To determine the optimal burning temperature of SSA for the replacement.
1.4 SCOPE OF STUDY
To obtain more accurate result, the scope of study for this research is set. The
sewage sludge used in this research was obtained from Indah Water Konsortium (IWK),
sewage treatment plant at Kuantan, Pahang. The temperature of incineration of sewage
sludge was set to 600°C and 800°C of burning. The mortar mix was designed according
to the standard ASTM C1329-05, type N strength mortar, where the proportion of sand
to cement to water is 2.75: 1: 0.6. The percentages of replacement of mass of the cement
in mortar were set to 10% and 15%. For the hardened properties tests, each specimen
was moulded into cube size 50 mm x 50 mm x 50 mm. The control mortar, mortar with
partial replacement of SSA (10% and 15%) that incinerated at temperature 600°C and
800°C were tested. The specimens were tested at 1, 7, 28 and 90 days. For each curing
age, three specimens were tested to get the average result.
1.5 RESEARCH SIGNIFICANCE
The problems triggered by the disposal of sewage sludge waste make us realize
that landfill is not the appropriate option for the sludge disposal. This research is able to
review the feasibility of sewage sludge ash application in Malaysia. Through this
research, the properties and characterization of sewage sludge in Malaysia was
determined. Chemical composition is the fundamental study for an unknown material.
However, there are only limited researches on the sewage sludge ash in Malaysia.
Hence, various tests were conducted in this research to study the chemical composition
5
and microstructure of sewage sludge and sewage sludge ash. Besides, this study was
conducted to determine the optimal burning temperature for the production of SSA. The
SSA thermal study can further determine the least energy consumption for the
production of SSA. At the same time, the optimal percentage of SSA replacement was
determined through this research. The optimal replacement percentage of SSA indicates
the effectiveness of SSA to be reused as construction materials.
The results from the experiments that were carried out in this research can show
the mechanical performance of the mortars with SSA replacement. The mechanical
strength achieved by the SSA mortar in this research is able to shows the capability of
SSA mortar to be applied for structural purpose. The total porosity test determines the
durability and long term function of the SSA mortar. Furthermore, it evaluates the
resistance of the SSA mortar toward water and other soluble chemical. In a nutshell, this
research can be a milestone for future researcher to delve further into the application of
sewage sludge.
On the other side, this research can shows that the capability of sewage sludge
ash as an alternative for the use of cement which is favorable from the environmental
and economic perspective. After the heat treatment, the organic content and pathogen in
sewage sludge will be completely removed as suggested by Wang et al. (2012). The
replacement of SSA into mortar is able to reduce the amount of sewage sludge disposal
to the landfill. Additionally, the pollution and disease triggered by the disposal of
sewage sludge will be minimized. The reuse of SSA as construction material provides a
great opportunity to reduce depletion of resources. Cement is one of the most widely
use construction materials and is rather expensive as compared to other materials. The
construction cost can be directly cut down by replacing the cement with SSA.
6
1.6 EXPECTED OUTCOME
The expected outcome for this research is:
1. There is no significant decrease in compressive strength after the sewage sludge
ash is added to mortar as cement replacement.
2. There is no significant increase of the mortar total porosity after the partial
replacement of SSA to cement.
3. The optimal percentage of SSA replacement to the mass of cement is either 10%
to 15%.
4. The optimal burning temperature of SSA is between 600°C to 800°C.
CHAPTER 2
LITERATURE REVIEW
2.1 INTRODUCTION
This chapter contains the review of past relevant literatures such as the study of
SSA to be utilized in agriculture field and construction field. The information and data
from the past literature were summarized in this chapter where the scope of study in this
research can be set. In the meantime, this chapter also shows the comparison between
different by-products that can be used as cement replacement material such as fly ash,
risk husk and sawdust with the sewage sludge ash.
2.2 NATURAL BY-PRODUCT AS CEMENT REPLACEMENT MATERIAL
Fly ash is the by-product from the burning of coal, while the ash that remains at
bottom after combustion is called bottom ash. Fly ash has been studied to be used in
high performance concrete. Fanghui et al. (2015) stated that ground fly ash is able to
replace 20% to 40% of the cement mass. The additive of fly ash can reduce the CO2
emission during the hydration of cement. Besides, the reuse of fly ash as cement
replacement can greatly reduce the waste problem and save energy. Narmluk & Nawa
(2011) found that the replacement of fly ash retard the hydration process of cement at
early stage but accelerate the hydration a later stage. In the study on the engineering &
material sciences, Christy & Tensing (2010) reported that the replacement of 10% of fly
ash has higher value of compressive strength as compared to control mix at 28 days of
curing. The similarity of sewage sludge ash and fly ash is the delay of hydration process
when added into cement based materials. The application of fly ash in cement is already
8
available in the market and this shows the potential of by-product being reused as
cement.
Rice husk is an agriculture waste product and is disposed by dumping or burning.
Meanwhile, rich husk ash or RHA is a by-product of the burning of rice husk. Obilade
(2014) found that RHA can be a good pozzolan to be beneficial reused as cement
replacement. The optimum replacement of RHA to the mass of cement is ranging from
0% to 20%. Dabai et al. (2009) carried out chemical analysis on the RHA and reported
that RHA consists of high content of silicon dioxide, 68.12%, aluminium oxide, 1.06%,
calcium oxide, 1.01% and iron oxide, 0.78%. Those chemical properties are responsible
for the pozzolanic activity in cementatious materials. Dabai also concluded that the
compressive strength of the concrete with 10% of RHA replacement is decrease for 11%
as compared to the control sample. The strength continues to decrease with increase in
RHA replacement to the mass of cement. Sewage sludge ash and rice husk both has
high content of chemical composition such as silicon dioxide, aluminium oxide and
calcium oxide which is the major content of cement. However, the different between
sewage sludge ash and rick husk is that sewage sludge ash might consist of high amount
of heavy metal as compared to the rice husk. Heavy metal may raise health issue if the
amount is significant.
Sawdust or wood dust is waste from the cutting and grinding of wood. Sawdust
ash, SDA is the product from the burning of sawdust. Ettu et al. (2013) states that 5% to
20% of SDA can be used to replace cement in cement based materials. The compressive
strength of 10% replacement of SDA to the mass of cement is 18% lower as compared
to pure OPC concrete. The replacement of SDA shows some reduction in compressive
strength of concrete. Raheem & Sulaiman (2013) conducted experimental works for the
replacement of cement with SDA to produce walling material. It was concluded that 10%
of SDA is the optimal percentage of cement replacement to produce non-bearing wall.
Researches have been done on various by-products or waste materials for them
to be utilized to replace cement. The partial replacement of by-product to the cement
can save the construction resource and at the same time reduce the waste. The
compressive strength of various by-product are summarised by Agrawal et al. (2014)
9
where the highest compressive strength is achieved by replacement of fly ash, follow by
pumice fine aggregate, paper mill sludge ash, crumb rubber, sewage sludge ash, rice
husk ash and class F-fly ash. By comparison, replacement of fly ash has the highest
compressive strength. Fly ash is already been using as admixture to the cement to
produce CEMII in Malaysia while there is only limited studies on sewage sludge ash in
Malaysia. Hence this research is conducted by using sewage sludge ash as partial
replacement. The performance of mortar with SSA replacement in this research can
shows the potential of SSA to be beneficial used as binder material.
2.3 MORTAR
Portland cement mortar is a material made from the mixing of sand, cement,
water and other additive. Cement mortar commonly casted as a paste that is applied in
masonry construction to bind building block such as bricks and masonry units together.
The proportion of the mortar ingredients or the mix design of the mortar is critical for
the strength development in mortar. In order to study the hardened properties of the
SSA mortar, Monzó et al. (1999) casted the mortar with SSA replacement in mortar
mould with dimension of 40 mm x 40 mm x 160 mm. The mortar mix was designed
according to the ASTM C-305 with 450 g of ordinary Portland cement (OPC), 1350 g
of fine aggregate, 4.5 g of superplasticizer and 200ml of water. Besides, the preparation
of SSA mortar mix in the research (Pan et al., 2003) was according to the ASTM C109
and ASTM C311 with mix proportion of 1375 g of fine aggregate, 400 g of OPC and
100 g of SSA. On the other side, Wang et al. (2009) prepared the mortar mix with
cement to fine aggregate ratio of 1: 2.75, as regulated by ASTM.
In this research, the cement that was used for the preparation of SSA mortar is
OPC. The mortar mix was designed according to ASTM C1329-05, a type N strength
mortar, where the proportion of sand to cement to water is 2.75: 1: 0.6. The mortar paste
is moulded into 50 mm x 50 mm x 50 mm cube for the hardened properties tests.
10
2.4 BY-PRODUCT FROM MUNICIPAL WASTE
Sewage sludge is the by-product from municipal waste such as human excreta,
commercial waste, industry waste, agriculture waste, rainwater runoff and biological
waste material. The municipal waste is carried to the sewerage treatment plant through
sewer to be treated. After treated, the sewage sludge will be dried at the sludge bed. The
dried sewage sludge becomes a waste and disposes to the landfill. Usman et al. (2012)
defined sewage sludge as a rich source of organic nutrients, which is high concentrate of
organic matter, macro and micro nutrient. The nutrient rich content of sewage sludge
shows the potential of being reused as fertilizer. Meanwhile, untreated sewage sludge
may consist of 60% to 80% of moisture content. In this research the moisture content
are removed by oven dry and incineration of sewage sludge. Table 2.1 shows the
different types of sewage sludge and the method of handling.
Table 2.1: Type of sewage sludge and its characterization
Sewage Sludge Method and Characterization
Liquid Sludge Containing 2% to 7% of dry solid and 75% of the solid is organic
matter
Untreated
Sewage Cake
Dewatered of liquid sludge, consistency similar to soil.
Conventionally
treated sludge
Subjected to digestion, where 99% of microbiological content are
removed.
Enchanted
treated sludge
Pathogen is eliminated, sludge is in form of granules where 98% if
dry solid.
Source : Usman et al. (2012)
Rosenani et al. (2004) recorded that the sewage sludge from Malaysia is acidic
and has an average low pH level which is about 4.9, 3.6 and 4.0 at different area in
Bungor, Serdang and Jawa. Rosenani also suggested that the acidic properties is due to
no lime is used during the treatment process of the sewage sludge. In other country,
calcium oxide, CaO is added during the sewage sludge treatment process. Since
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Malaysia has different sludge treatment process, sewage sludge ash produced in
Malaysia may content lower amount of CaO as compared in other country. Calcium
oxide is the major component in cement and is responsible for the hydration process
when react with water to produce primary strength to the cement paste.
The sewage sludge used in this research is untreated sewage cake on the sludge
bed. The untreated sewage sludge cake is oven dried and burnt at high temperature to
produce sewage sludge ash. The properties of SSA is determined and reused as binder
material replacement. The sewage sludge for this research is obtained from IWK
Kuantan, Pahang which the sludge is categorized as domestic sludge.
2.4.1 Utilization of Sewage Sludge for Agricultural Purpose
The utilization of sewage sludge for agriculture purpose is getting popular as an
alternative for sewage sludge disposal. In Malaysia, Rosenani et al. (2004) attempted to
study the characterization of the soil treated with sewage sludge. The laboratory
experiment shows that Malaysia sewage sludge is acidic in nature. The soil treated with
sewage sludge consists of nitrogen, phosphorus, calcium, potassium and magnesium.
The concentrations of heavy metal such as Pb, Cd, Cu, Ni, Mn and Zn are 100, 3.41,
257, 32, 189.1 and 1986 mg kg-1
respectively. Meanwhile, Zhen et al. (2012) conducted
a study on the potential of applying sewage sludge waste as fertilizer to yield Philippine
grass. After the observation from the crops growth Zhen et al. (2012) found that 13% of
waste sludge concentration can be incorporated in fertilizer. The utilization of 13% of
sewage sludge has significantly increases the yield of Philippine grass. Sewage sludge
provides high nitrogen concentrate and did not increase the enterococci in the soil.
Contrary, Siti Noorain Roslan and Siti Salmi Ghazali (2013) states that sewage
sludge in Malaysia has lower fertilizer properties as compared to commercial fertilizer.
Sewage sludge contains 3.2% nitrogen, 2.3% phosphorus and 0.3% potassium while
commercial fertilizer contains 5% to 10% nitrogen, 10% phosphorus and 5% to 10%
potassium. The sewage sludge is taken from Indah Water Konsortium (IWK) waste
water treatment plant located in Sungai Udang, Melaka. At the same time, Rosenani et
al. (2004) and Siti Noorain Roslan and Siti Salmi Ghazali (2013) concluded the sewage
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sludge in Malaysia may consist of high content of heavy metal and not suitable for
agriculture purpose.
In Iran, Ahmed et al. (2010) reported that the utilization of sewage sludge for
soil conditioning will lead to the lowering of the pH level of the soil. Electrical
conductivity of the soil increased for about 4.48 times higher than the control soil. The
result from the test shows the soil with sewage sludge has higher content of nitrogen
and phosphorus which has the ability to improve the soil quality. However, the yield is
decreases due to the high heavy metal content in the sewage sludge. Heavy metal can
cause the retardation of crops growth. The source of sewage sludge at Iran is very poor
for agriculture use.
In conclusion, the application of sewage sludge in agriculture is able to improve
the level of nitrogen and phosphate of soil. The sewage sludge has fertilizer properties
that can improve the condition of the soil. However, Rosenani et al. (2004) shows that
the sewage sludge in Malaysia has acidic properties and how it affect the crop growth.
The study from Rosenani concluded that sewage sludge in Malaysia may not suitable to
be reused as fertilizer due to high content of heavy metal. Upon this issue, this research
will be conducted on the utilization of the sewage sludge as construction material where
the problem triggered by heavy metal content will be less significant.
2.4.2 Utilization of Sewage Sludge as Building Block
In a study of waste management, (Cusidó & Cremades, 2012), it was found that
the sewage sludge can be reused to produce building block or brick. Waste sewage
sludge ranging from 5% to 25% of the brick weight can be incorporated into brick.
More than 25% of replacement will cause deterioration to the mechanical properties of
the clay brick. The clay brick is produced by mixing of clays, sludge and saw dust.
Leaching tests according to the standards NES 7345, ESA PSS-01—729 shows that the
reused sewage sludge brick does not have any environment restriction. The
concentration of heavy metal inside the clay brick is not significant hence there is no
health risk for using sewage sludge brick. The brick has become lighter and more
thermal and acoustical insulate than conventional clay brick. The reuse of sewage