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International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 6, June 2017, pp. 567–583, Article ID: IJCIET_08_06_063
Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=6 ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication Scopus Indexed
THE EFFECT OF PARTIAL REPLACEMENT OF
WASTE WATER TREATMENT SLUDGE ON
THE PROPERTIES OF BURNT CLAY BRICK
V.Y Katte, J.F.N Seukep and A Moundom
Department of Agricultural Engineering,
Faculty of Agronomy and Agricultural Sciences University of Dschang Cameroon
A.S.L Wouatong
Department of Earth Sciences, Faculty of Science, University of Dschang,
K.B. V Kamgang
Higher Teacher Training College, University of Yaounde, Cameroon.
ABSTRACT
This study seeks to utilize wastewater sludge for use in clay brick production. Both
materials-sludge and clay were characterized to determine their properties. Then
compositions of clay-sludge were made by introducing 0,10,15,20,25,30,35 and 40%
of sludge into clay. Cubic and cylindrical test specimens were made using a manually
operated hydraulic press. These were dried at 105°C and fired in a programmable
electric kiln having a temperature increase of 100°C and at a rate of 5°C/min up to a
maximal temperature of 1050°C. These were left at the maximal temperature for 2
hours after which the temperature was lowered progressively. The following
properties were determined: weight loss on ignition, linear shrinkage, bulk and
absolute density, water absorption, water suction, efflorescence, compressive strength
and leaching of heavy metals. The results indicate that addition of sludge causes
efflorescence and that up to 15% sludge can be incorporated into clay bricks with a
resultant optimal compressive strength of 11.6MPa. This value is above that
prescribed by the French norms NF P13-304. Also at this acceptable composition
water absorption, water suction, efflorescence, linear shrinkage and loss of mass were
within the acceptable limits. Leachates obtained from crushed brick specimens showed
low levels of heavy metals indicative that these were immobilized in the ceramic
matrix during the sintering process. Therefore the bricks are environmentally friendly.
Key words: Wastewater sludge, clay, bricks, firing, leachates, compressive strength,
sintering.
Cite this Article: V.Y Katte, J.F.N Seukep, A Moundom, A.S.L Wouatong and
K.B. V Kamgang The Effect of Partial Replacement of Waste Water Treatment Sludge
on The Properties of Burnt Clay Brick. International Journal of Civil Engineering and
Technology, 8(6), 2017, pp. 567–583.
V.Y Katte, J.F.N Seukep, A Moundom, A.S.L Wouatong and K.B. V Kamgang
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1. INTRODUCTION
The rate of urbanization in Africa is putting an enormous pressure on the available resources
such as local construction materials. Concurrently the population increase has a resultant
effect on environmental sanitation especially the disposal of wastes (solid and liquid).
Yaounde the capital city of Cameroon currently has a population of about 2.6 million
inhabitants and is experiencing an urbanization growth rate of 6-7% (Djayou, 2008). From the
estimates of INS, 2010, Cameroon has a population growth rate of about 2.6% with the
possibility of the rate doubling to 5.2% by 2037. Consequently, there will be an upsurge of
solid waste and wastewater production which will have dire consequences on the environment
if definite steps are not taken into consideration to redress the current situation. Fortunately
government has envisage to construct second generation wastewater treatment plants that will
improve upon the rate of wastewater treatment from 34% in 2010, to about 57% by 2020
(MINEE, 2011). In the light of this, Yaounde would countabout 7 of such treatment stations
by 2020 capable of producing about 6400 tons of dry sludge matter. This is a major step at
curbing urban pollution, with the principal preoccupation being the management of enormous
amount of sludge generated from these wastewater treatment plants. Another government
policy is the encouragement to use local materials for construction. The aim is to reduce the
cost of building materials as well as reduce environmental degradation and also create
opportunities foremployment creation. It is in a bid to attain these objectives of rational
utilization of materials and environmental protection that this research was carried out
whereby an optimal quantity of sewage sludge that could be incorporated in burnt brick
production was determined.
2. HISTORICITY OF BURNT BRICK PRODUCTION
Burnt clay brick production in Cameroon dates back to the colonial era where major buildings
were constructed with clay. Since independence this material has not been utilized as would
have been expected. The emergence of modern clay brick production is awaited nationwide,
though currently some artisanal production is still very rudimentary. Burnt clay brick is a
construction material generally having a rectangular cuboid shape, which may be plain,
perforated either vertically or horizontally. It is obtained by molding an argillaceous material
mixed with the necessary additives to the required dimension followed by firing between 900-
1100°C(Melo & Lemougna, 2012).. The argillaceous material must have a clay content of at
least 20% (kaolinite, illite, smectites)
3. DESCRIPTION OF STUDY AREA
Yaounde is located at about 250 km from the Atlantic Ocean between latitudes 3° and 5°
North and longitudes 11° and 12° East. It has an equatorial type climate of the Guinean type
with alternating two dry seasons and two wet seasons. The subbasement is made up of
Precambrian rocks which consist essentially of crystalline rocks (granites, gneiss
micaschistes). According to Belinga & Kabeyene 1982, the soils developed on these are
ferralitic, which have as physicochemical characteristics an argillaceous texture with a
dominance of kaolinite and iron hydroxide. It has a low pH < 5.5 and is lowly mineralized.
The lateritic horizons serve as a good disposal sites for biological waste Segalen 1967. In
areas where there is a shallow water table, the risk of water pollution is very high (Ondoua,
2001). The hydro geological characteristics of Yaounde are of the crystalline type which
contributes more to groundwater recharge than to stream flow recharge (Dim, 1992). The
hydrologic system is made up of the following rivers Mfoundi and Ntem in the North;
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Ntongou, Ekozoa, Abiergue and Mingoa in the West; Djongolo in the East; Olezoa, Ebogo,
Ewoute, Ake and Odza in the South.
Figure 1 Localization of study area
4. MATERIALS AND METHODS
4.1. Characterization of clay material
The clay material was collected at Etoa 4km southwest of Yaounde located between the
valleys of M found in the North and Mefou in the South. It was carried to a laboratory where
it was air dried and latter pulverized. The clay material to be utilized was quartered until the
desired quantity was obtained. Preliminary test carried out on the material include specific
gravity, apparent density, particle size analysis, Atteberg limits tests, X-ray diffraction
analysis and X-ray chemical fluorescence tests.
5. TESTING PROCEDURES
5.1. Specific gravity test:
This test was carried out in accordance with French standards NF P 94-054 (1991). It is given
as the ratio of the particle mass to its volume. G� ���
�� where ms is the mass of particle solids
and vs is the volume of particle solids. A pycnometer of volume 250 ml is dried in an oven
and thereafter its mass was determined m1. Thereafter 25 g of soil material, oven dried and
passing through a 1 mm sieve is weighed in the pycnometer and mass m2 recorded. The
pycnometer with the soil sample was half filed with water and vacuumed till all air bubbles
are out. Thereafter it was filled to the 250 ml mark with distilled deaired water and the weight
m3 was obtained. Thereafter the pycnometer was emptied and well cleaned and then filled
with distilled water to the 250 ml mark and the weight m4 determined. The particle density is
given as:
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G� �m�
v�
� − �
� + − � − ��
5.2. Apparent Density
The apparent density of a soil is the density of the soil containing voids of air within. This was
determined in accordance with the French norms NF P 98-250-6(1991). The soil material was
weighed on a balance and mass m1 was determined. The soil mass was coated with melted
paraffin wax with density ρp and allowed to cool in air. The waxed soil material was weighed
on a balance m2 and thereafter immersed in a graduated glass cylinder containing a known
volume of water. The displaced water volume V was recorded. The apparent density was
determined as:
�� ����
��� − − ��
5.3. Particle Size Analysis
The grain size analysis for particles having grain size larger than 80 µm was carried out by
sieve analysis according to the French Norms NF P 94-056 (1996). This entails washing 400g
of the soil material until it is clean on a sieve of size 80 µm. Thereafter the washed material
was placed in an oven at 105°C for 24 hours. The dried material was then removed from the
oven and allowed to cool and then sieved through a series of sieves of decreasing sieve sizes
1000 µm, 500 µm, 400 µm, 250 µm, µm, 125 µm and 80 µm, arranged in a column by
vibration for a period of 5 minutes. After which the material retained on each sieve was
carefully weighed on a balance. The cumulative mass on each of the sieves must equal the
mass of oven dried as withdrawn from the oven. The percentage passing each sieve was then
plotted against the grain size.
The particle size analysis by sedimentation was carried out in accordance with the French
Norms NF P 94-057 (1996). 40g of oven dried soil material obtained from sieve sizes 100-80
µm was well homogenized using a rubber piston and thereafter placed in a cylindrical jar
containing 440 cm3 of distilled water. 60 cm
3 of a deffloculant sodium hexametasulphate was
added and allowed for a period of 15 hours. The content of the jar was agitated for 3 minutes
and the content was emptied into a 1000 ml glass jar and the content rinsed thoroughly with
distilled water until 1000 ml mark was attained. The whole was again agitated for three
minutes after which a hydrometer was introduced into the glass cylinder and the particles
sizes were estimated from Stokes law at time intervals of 30s, 1min, 2min, 5min, 20min, 40
min, 80min, 240min, and 1440minutes by the use of a stop watch. The particle sizes are
plotted on the previous graph to obtain the full grain size distribution curve.
5.4. Atterberg Limits Tests
The Atterberg limits tests of the liquid limit and plastic limit was determined in conformity
with the French Norms NF P 94-051(1993). The soil sample of mass 500 g was soaked in
water after which it is washed through a sieve of size 400 µm. The material passing through
the sieve was collected and allowed to settle, after which the material obtained was utilized
for the test. The liquid limit is the water content at which a soil moves from the dry state to
the plastic state. It was determined as follows: about 70 g of the paste is grooved into a
Casagrande bowl to a thickness of about 1cm. With the aid of a grooving stick, a V groove
line 2mm wide was made at the center diving the Casagrande bowl into 2. The Casagrande
bowl was allowed some number of blows till the V groove closed. The number of blows was
recorded and the some soil was removed for water content determination. This procedure was
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repeated five times with decreasing water content such that the number of blows was
between15-35. The values are plotted on a water content versus number of blows curve and
the water content at 25 blow gave the value of the liquid limit.
The plastic limit is the water content at which a soil sample passes from a plastic state to a
semi solid state. The value of the liquid limit was higher than the value of the plastic limit. It
is carried out by leaving the soil material to dry-out. When the correct consistency was
attained, a ball of about 12cm diameter was rolled to threads of about 3mm diameter such that
these threads do not rupture. When these threads are lifted up between 15 to 20mm high and
no rupture was produced, then the plastic limit was attained. The threads were then subjected
to water content determination and the value obtained gave the plastic limit. The plasticity
index was obtained from the difference between the liquid limit and the plastic limit and was
given as:
PI � LL − PL
5.5. Methylene Blue Test
60 g of soil with particle size 2 mm was placed in a container and 500 ml of distilled water
was added and agitated in a magnetic stirrer at a speed of 400 rev/ min for a duration of at
least 5 minutes. Thereafter 5 ml of a solution of methylene blue was added using a graduated
burette and after 1 minute, the test was carried out on a filter paper as follows; with the aid of
a dripper a drop of the suspension (8-12 mm) was placed on the filter paper and the resulting
stain was observed. The stain is usually made up of a central deposit of material with a light
blue coloration surrounded by a clear zone. The test was reckoned positive if within the
humid zone there appeared a persistent blue coloration. The test was negative if the central
spot of the stain was not colored, and in this situation, 5 ml of methylene blue was again
added. The setup was allowed for the absorption of the blue to take place and this usually took
some time. There was a minute by minute monitoring of the blue color and in case the blue
color disappeared let’s say at the fifth minute, then this was followed by further injection of 2
ml of methylene blue followed by a minute by minute monitoring. This operation was carried
on till the test became positive and remained so within five consecutive minutes. The value of
the methylene was determined by the expression
��� � 10 ∗�
Where VBS = value of methylene (g.100g-1), v = total volume of blue absorbed, m =
mass of the droplet (g)
5.6. Specific Surface Area Test
The total specific surface is evaluated by the expression given Santa marina et al., 2002 as
�� � ��� ∗ !
Where Sp = specific surface, VBS = value of methylene (g.100g-1), CF = correction
factor ≈ 20.94
5.7. Organic Matter Content
This was carried out in accordance with the French norms NF P 94-047 (1998). 5 g of the
pulverized soil sample was placed in a pre-weighed crucible of mass mo and the total weight
determined m1. This was then introduced into a kiln and calcined at 800⁰C for a period of one
hour. Thereafter the crucible was removed and placed in a desiccator and allowed to cool for
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10 minutes and cooled weight m2 of the crucible was determined. The organic matter was
determined by the expression
"# �� − $
− $
& 100
Where OM = organic matter content (%), m0 = mass of crucible, m1 = mass of
specimen and crucible before calcinations, and m2 = mass of crucible and calcined
specimen.
5.8. X-ray Diffraction Analysis (XRD)
This was carried out by the diffraction principle as given by Klug and Alexander 1974. The
soil specimen was dried and pulverized to powder and then introduced into a Bruker diffract
meter of type D8 having a copper cathode with a speed of 0.01 2 s-1 at an acceleration of 40
kV and an intensity of 40 mA.
5.9. X-ray Chemical Fluorescence Test
X-ray fluorescence enables the determination of the chemical components of the principal
elements in the soil materials. This was carried out on clay samples using a Bruker
spectrometer of type S 4 pioneer as given by Jenkins (1932)
6. WASTEWATER SLUDGE EXTRACTION, TREATMENT AND
CHARACTERIZATION
The wastewater sludge was collected from the Cite Verte neighborhood wastewater treatment
plant of the city of Yaounde. It was placed in a drying platform constructed within the site of
size 9m2. Drainage was achieved through a granular material of course gravel (15mm) of
0.3m3 over which sand of 0.5m
3 volume was placed. The preliminary tests carried on the
wastewater sludge in order to characterize it include: the water content, the dry matter
content, pH, organic matter content, chemical analysis, heavy metal content and the fraction
of leached heavy metal. A summary of these procedures are given below.
6.1. Water Content
The water content test was carried out in accordance with the French norms NF P 94-050
(1995). Material of a known weight ww was placed in an oven at 105°C for a period of 24
hours. After which the material was removed from the oven and allowed to cool to room
temperature and reweighed wd. The water content was calculated as:
#'() �*( − *+
*+
& 100 %
Haoua (2007) has defined dryness as the percentage of dry matter in the sludge and is
obtained by the expression below as:
� � 1 − #'()
Where S= Percentage of dry matter, Mcwb = water content (%), ww= mass of wet material,
and wd= mass of dried material
6.2. pH
The pH was determined in accordance with the international norms ISO 10390 (1994). It
consisted of preparing a suspension of the sludge of a given volume by dissolving it with a
volume of distilled water five times that of the sludge volume. The suspension was agitated
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with a magnetic stirrer for five minutes after which the pH was determined using an electronic
pH meter.
6.3. Organic Matter Content
This was carried following the procedure as explained previously.
6.4. Chemical Analysis
This was carried by X-ray fluorescence following the procedure as explained previously.
6.5. Determination of Heavy Metal Content
This was determined in accordance with ISO 11460. It consisted of introducing 0.5 g of
powdered sludge into a mixture of 30 ml water and (1/3 HNO3 + 2/3 HCL). This mixture was
heated at 100°C until the partial evaporation of the acid, after which it was left to cool in
ambient air. After cooling, the mixture was placed in a cylinder of 50ml and distilled water
was filled to the 50ml mark. The mixture was then filtered using a glass fibre membrane of
pore size 0.45μm. The heavy metal concentrations were determined by atomic absorption
spectrometer. The metals were identified by X- ray fluorescence.
6.6. Leached Metal Content
The purpose of this test was to find out the amount of heavy metal leached out from the brick
specimen. The different concentrations of heavy metals in the leached fluid was compared
with European standards. The test consisted in carrying out a leaching test using
demineralized water for 24 hours with a liquid/solid ratio of 10 in conformity with European
norms 12457-2 (2002). The leacheate was filtered using glass fibre filter of pore size 0.45 μm
and analysed by atomic absorption spectrometer.
7. LABORATORY PREPARATION OF BRICKS
The materials namely dried the wastewater sludge and clay was placed in an oven at 105°C
for 24 hours to eliminate any residual moisture. After which these were separately pulverized
and sieved using a sieve size 400μm. The various compositions consisting of sludge and clay
is given in the Table 1 below. Thereafter proper mixing was carried out with the required
volume of water manually in a bid to obtain a well homogenized paste. Since humidity
control is very important in confectioning so as to obtain constant mechanical characteristics
of the paste, the amount of water used for the control was 12 % while that for the other
compositions variedbetween 14-16% as given in Table 1. Two specimen brick types were cast
using a manual hydraulic press. The first consisted of cubic specimens 4cm x 4cm x 4 cm
while the second was cylindrical of 7cm diameter and 1.5cm height in accordance with
French norms NF P 13-304 (1983). In order to obtain the appropriate mass of paste required
for the 4 cm cubic specimens, various trials were carried out utilizing various mass of paste
and the resultant 4cm brick obtained was evaluated. Optimal results were obtained at 100g for
the 4 cm cubic bricks specimens and similarly 120g for the cylindrical specimens. After the
specimens were made they were left in a humidity chamber at a temperature of 20 ± 5°C and
relative humidity 60 ± 5% after which they were dried in an oven at 105°C until a constant
weight was obtained so as to eliminate any residual moisture which could cause fissures
during firing.
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Table 1 The compositions utilized in making the brick
Compositions Percentage of sludge
(%)
Percentage of clay
(%)
Percentage water
content (%)
Quantity of
water (ml)
B0 (control)
B10
B15
B20
B25
B30
B35
B40
0
10
15
20
25
30
35
40
100
90
85
80
75
70
65
60
12
14
14
15
15
15
16
16
20.4
24.0
26.4
27.6
28.8
28.8
30.0
30.0
Brick firing was the last stage and must be paid close attention so as to avoid breakage.
Ngon Ngon (2007) obtained excellent ceramic properties using the Etoa clay at a firing
temperature of 1050°C. The firing was carried out using a programmable electric kiln having
a temperature increase of 100°C and at a rate of 5°C/min up till a maximal temperature of
1050°C. The specimens were left at this maximal temperature for 2 hours after which the
temperature was lowered progressively. The specimens were then removed from the kiln and
a series of tests carried out on them to determine their mechanical characteristics. The tests
carried out include the determination of the physical properties, mechanical properties and
environmental characteristics.
8. PHYSICAL PROPERTIES OF THE BRICKS
The following specific tests were carried out: linear shrinkage, loss in mass, water absorption
capacity, water suction test and efflorescence test. Tests already carried out will not be
described again.
8.1. Linear Shrinkage
This was the linear loss in length of each of the specimen dimensions after firing using a
Vernier caliper with a precision of ± 0.01 mm. It was evaluated using the expression
-. �./ − .0
./
1 0// %
Where Rl = linear shrinkage, l0= length before firing and l1 =length after firing
8.2. Water Absorption
This test consisted in totally immersing the five specimens of each formulation in
dematerialized water for a period of 24 hours at a temperature of 20 ± 5°C and at atmospheric
pressure. Prior to carrying out this test the specimens were oven dried at a temperature of
105°C and cooled in a desiccator. The mass obtained after removal from the desiccator was
recorded as m0. After immersion the specimens were cleaned lightly with an absorbent cloth
and its mass m1 was determined. The water absorption was determined by the expression
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23 �40 − 4/
4/
1 0// %
Where Aw= absorbed water (%), m0= mass of dried specimen, and m1= mass of immersed
specimen.
8.3. Water Suction Test
This is obtained by measuring the volume of water absorbed by the brick upon a short partial
immersion in water for a period of 1 minute at the ambient laboratory temperature. The
specimen height is 1cm; the dry mass is measured md, the mass after immersion in water mh.
The water suction is expressed by
35 �46 − 47
5. 9
Where ws= water suction (g/cm2.min), mh= mass of immersed specimen (g), md= mass of
dry specimen (g), s= surface area of specimen (cm2) and t= duration of immersion =1 minute.
8.4. Efflorescence
The test of efflorescence was carried out on three cylindrical specimens each placed
individually in a container such that the diameters were immersed in demineralized water
vertically at a depth of 2 cm. A plastic film was used to cover the containers except for the
specimens which were exposed to free air in a humidity chamber at a temperature of 20 ± 5°C
and relative humidity of 60 for a period of 4 days. After which the whole set up was placed in
an oven at 60°C. If the specimens showed signs of efflorescence then they were cleaned
lightly with a dry rag three times and then they were further observed to determine if the
efflorescence have disappeared or not.
9. MECHANICAL PROPERTIES
A uniaxial compressive test was carried out on seven specimen of each of the formulations
using automatic compressive strength testing equipment having a capacity of 30 kN and at a
rate of 10 mm/min of ELE make. The specimens were placed on the platens of the
compressive machine and the force applied till rapture was observed. The compressive
resistance was evaluated from the force exerted at rupture divided by the surface area of the
specimen.
-: �;-
2
Where RC = compressive resistance (MPa), FR=rupture force (N), and A= surface area of
specimen (m2)
10. RESULTS AND DISCUSSION
The results of the preliminary analysis of the clay material are given in Table 2 and the
particle size distribution of the clay material is shown in Figure 2. The results of the X-ray
chemical fluorescence test carried out on the clay giving the various chemical composition
and their relative percentages is given on Table 3. The mineralogical composition of the clay
and the elemental percentage composition of the clay are shown on Table 4 and 5
respectively. This clay material is classified as a fine grained low activity clay or inorganic
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soils plotting above the A line on the plasticity chart, denoted as CL. The result from the
methylene blue test with value 2.1 is indicative that the clay is of low plasticity. The specific
surface of low activity clays is in the tune of 15 g/m2. However the value of 43.97 g/m
2
obtained from the Etoa clay may be attributable to organic matter which increases its
reactivity. The clay material has the first four high percentage chemical compositions being
SiO2 54.94%, Al2O3, 23.41 %, organic matter 10.52 % and Fe2O3 4.79 %. The rest of the
chemical compounds were less than 1 % but for TiO2 having 1.85%
Table 2 The preliminary analysis of the clay
Clay Characteristics Values
Color
Specific gravity
Particle density (g/cm3)
Specific surface (m2/g)
Vbs (g.100/g)
LL
PL
PI
Grey
2.66
1.90
43.97
2.1
42.46
25.34
17.12
Figure 2 Particle size distribution of clay
Table 3 Chemical composition of the clay
Chemical Composition Percentage (%)
Al2O3
SiO2
BaO
CaO
Fe2O3
K2O
MgO
Mn2O3
Na2O
P2O5
23.41
54.94
0.07
0.49
4.79
0.47
0.9
0.06
0.24
0.16
0
10
20
30
40
50
60
70
80
90
100
0.0010.010.1110
Perc
en
tag
e p
assin
g
grain size (mm)
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TiO2
ZrO2
OM
1.85
0.04
10.52
Table 4 Mineralogical composition of clay
Element Kaolinite Quartz Geothite Rutile Anatase Gibbsite Halloysite Feldspar
Clay (%) 47.0 24.1 5.2 3.4 4.8 3.6 4.0 1.9
Table 5 Elemental percentage composition of clay
Element O Al Si Ba Ca Fe K Mg Mn Na P Ti Zr
Clay (%) 42.85 12.39 25.68 0.06 0.35 3.35 0.39 0.54 0.04 0.18 0.07 1.19 0.03
Similarly, the results of the preliminary physical analysis of the wastewater sludge is
given on Table 6, while the X-ray chemical fluorescence test revealed various chemical
compounds and their percentage compositions are shown on Table 7. The major elements in
the sludge are silica, calcium oxide, aluminum oxide, iron oxide, sulphur oxide with the
organic matter taking the bulk. The higher percentage of the silica among the chemical
elements may have come from the sand bed on which the sludge was dried. Equally the
presence of oxides of heavy metals is evident from the percentages obtained. This therefore
implies some environmental concerns must be addressed.
Table 6 Results of the preliminary analysis of sludge
Sludge Characteristics Values
pH
Water content
Dry matter content
9.7
15.2
84.8
Table 7 Chemical composition of sludge
Chemical Composition Percentage (%)
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SiO2
CaO
Al2O3
Fe2O3
SO3
P2O5
K2O
TiO2
ZnO
Cl MnO
CuO
ZrO2
Cr2O3
SrO
NiO
OM
37.6
4.06
3.9
3.96
3.1
1.19
0.594
0.476
0.0843
0.064 0.0516
0.034
0.0196
0.013
0.011
0.004
45.4
Total 99.9975
The heavy metals contents as well as their mobile fractions were calculated based on the
percentages of oxides present in the chemical composition of the sludge. These are presented
on Table 8. It is evident from this that the sludge have high contents of zinc (680 mg.kg-1
) and
copper (272 mg.kg-1
). The other metals Chromium and Nickel have low contents (68 and 31
mg.kg-1
respectively).On observation, figure 3 shows that the mobile fractions of each of the
heavy metals present in the sludge are inferior to the heavy metal content of the sludge.
Table 8 Heavy metal concentration and their mobile fraction in sludge
Element Concentration in sludge (mg/kg) Fraction mobile (mg/kg)
Zn
Cu
Cr
Ni
680
272
68
31
114
67
13.8
8.6
Figure 3 Concentration of heavy metals in the sludge and concentration leachable
0
100
200
300
400
500
600
700
800
Zn Cu Cr Ni
Co
nce
ntr
ati
on
of
he
avy
me
tals
(m
g.k
g-1
)
Heavy metals
Total concentation of heavy metals Concentration of mobile heavy metal
The Effect of Partial Replacement of Waste Water Treatment Sludge on The Properties of Burnt Clay
Brick
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The parameters which were used to evaluate the suitability of burnt bricks were the
shrinkage, loss in mass upon firing, water absorption, water suction and compressive strength.
Since the materials have some heavy metals therefore it was exigent to conduct some tests to
determine the extent of the leached heavy metals. The process of firing can cause some
dimensional changes (linear shrinkage) as well as the appearance of some dark spots
especially when the organic carbon is not completely burnt (Martinez et al., 2012). So far no
dark patches were found on the bricks but however dimensional changes and loss of mass
were observed as shown in Figure 4. Linear shrinkage is an important parameter in assessing
brick quality. This study reveals that the linear shrinkage decreases with increase in the
amount of sludge from 6.72 % with 0 % sludge to 1.37 % at 40 % sludge addition to clay.
This result would be logical if it was considered that the sludge did not contain quartz.
Martinez et al. (2012) stated that during the sintering process, the melting of the quartz
particles contributes to the further consolidation of the clay particles, hence the shrinkage.
However, since raw materials (clay and sludge) contained quartz in the respective proportions
of 54.94% and 37.6%, it is clear that the linear shrinkage of the specimens should therefore
increase rather than decrease. This reduction in shrinkage can thus be due mainly to the
organic matter present in the sludge, which volatilized during the firing process leaving voids
in the ceramic matrix of the bricks. Martinez et al., 2012 fixes a limit to linear shrinkage to a
value of less than 8%. The addition of sludge influences significantly the shrinkage with the
control specimen having a value of 6.92% as against 1.37 % for brick having 40% sludge.
Again Martinez et al., 2012 affirms that the firing process causes a fusion of quartz particles
which contributes to the consolidation of clay particles as it shrinks. Therefore greater
shrinkage occurs in the control specimen which consists of only the clay material having a
quartz content of 54.94 % as against the other specimens having varied sludge percentages
having a quartz content of 37.6%. On the other hand the results of the loss in mass after firing
gives a 9.26 % loss for the control specimen which progressively increases to 20.98 % for the
specimen having 40 % sludge. This can be attributable to the presence of organic matter in the
clay initially at 10.52% which volatizes and the loss of adsorbed mineral water from the clay
due to dehydroxylation and the decomposition of calcium carbonate (Martinez et al., 2012.)
Figure 4 The trend in linear shrinkage/loss in mass of the various compositions
The result of the water absorption is shown in figure 5. The coefficient of water
absorption increases as the percentage of sludge increases in the mix. The French standards
NF P 13-304 of 1983 gives a maximum value of 25%, therefore up to 20 % sludge
replacement is acceptable.
0.00
5.00
10.00
15.00
20.00
25.00
B 0 B 1 0 B 1 5 B 2 0 B 2 5 B 3 0 B 3 5 B 4 0
Pe
rce
nta
ge
sh
rin
ka
ge
/lo
ss i
n m
ass
Composition
Linear Shrinkage (%) Loss in mass (%)
V.Y Katte, J.F.N Seukep, A Moundom, A.S.L Wouatong and K.B. V Kamgang
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Figure 5 Results of the water absorption test of the various mixtures
The results of the water suction test on the bricks are given in figure 6 with the control
having the least value of 0.19 g/m2.min and against 0.64 g/m
2.min for specimen having 40%
sludge. According t to Martinez et al., 2012, the water suction of bricks should be less than
0.45 g/m2.min. Based on this up to 20% replacement of clay with sludge in brick is acceptable
Figure 6 results of the water suction test of the various mixtures
11. EFFLORESCENCE
Efflorescence results from the presence of small quantities of soluble salts in the primary
materials which becomes mobile in the presence of humidity and moves from the interior of a
porous system to the surface (Baldin et al., 1971). In principle all hydrosoluble salts are
susceptible to effloresce. The most frequent are lime (CaO) which is slightly soluble and in
presence of CO2 carbonates and effloresces into some whitish crystals. Other salts which
cause efflorescence include sulphates of sodium, potassium, magnesium, calcium and barium.
All the brick compositions showed signs of effloresce but for the control specimen, as shown
in Figure 7. The absence of efflorescence in the control specimen was evident because in the
clay material sulphate salts were absent and the lime content consists of only 0.49 %.
However the sludge was made up of 3.1 % of sulphite and 4.09 % of lime. There was
efflorescence on all the other mixtures but for the control and this is consistent with the
17.619.06
21.9624.23
25.61
28.78 29.0831.24
0
5
10
15
20
25
30
35
B0 B10 B15 B20 B25 B30 B35 B40
Co
eff
icie
nt
of
wa
ter
ab
sorp
tio
n
(%)
Composition
0.19
0.29
0.37
0.430.47
0.530.58
0.64
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
B0 B10 B15 B20 B25 B30 B35 B40
Wa
ter
suct
ion
(g
.m-2
.min
)
Composition
The Effect of Partial Replacement of Waste Water Treatment Sludge on The Properties of Burnt Clay
Brick
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increase of these soluble salts in the various sludge percentages incorporated in the bricks.
Samara 2007 prescribes the use of either BaCO3 or BaCl2 at a dosage of 7 kg per ton of clay
material in order to limit efflorescence.
Figure 7 (a) whitish crystals on some specimens, (b) cleaning of the whitish crystals
The compressive resistance of the various compositions is given on Table 9. The control
specimen without the addition of the sludge has a compressive resistance of 16.08MPa. When
10% of the sludge is added there is a 13% reduction of the compressive strength to a value of
13.91MPa. This reduction is attributable to the reduction in the density due to the combustion
of organic matter during firing creating more porosity at the detriment of the compressive
strength. These results are in conformity with the findings of Tay et al., 2002, Ramadan et al.,
2008 and Babu and Ramana, 2003. However only the compositions B10 and B15 had
compressive strength values higher than the minimum specifications of 10.0 MPa prescribed
by the French standards NF P13-304 for ordinary clay bricks.
Table 9 Compressive strength of the bricks
Composition Compressive resistance (MPa)
B0
B10
B15
B20
B25
B30
B35
B40
16.03
13.91
11.6
9.84
7.16
5.84
4.54
2.81
12. THE CHOICE OF AN ACCEPTABLE COMPOSITION
From the results obtained so far, the acceptable composition of clay and sludge required to
manufacture brick of acceptable quality meeting the compressive strength requirements by the
French standard is B15 which contains 15% sludge replacement of clay. An environmental test
was carried out on specimens having 15% sludge to determine the extent of leaching of heavy
metals following European and American standards as shown in Table 10 and Table 11.
V.Y Katte, J.F.N Seukep, A Moundom, A.S.L Wouatong and K.B. V Kamgang
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Table 10 Metal quantities released into the leach ate from the leaching test according to European
Standard
Elements Amounts Leached Tolerable limits for
inertb wastes
L/S=10
Tolerable limits for non
toxic wastes
L/S=10
Zn 0,08 4 50
Cu 0,05 2 50
Cr < 0,02 0,5 10
Ni < 0,02 0,4 10
Table 11 Metal quantities released into the leach ate to from the leaching test according to the
American standard
Elements Amount leached TCLPb limits
Zn 1,7 25
Cu 0,8 15
Cr < 0,2 5
Ni < 0,2 -
The results of Table 10 shows the quantity of leached elements do not exceed the
permissible limits required for landfills for inert waste. Similarly, Table 11 also shows the
heavy metal concentrations in the leachates following the TCLP procedure. These results
shows that the leached heavy metals are all below toxicity limits and are consistent with those
obtained by Samara (2007), and Joan & Lazaro (2012). This is due to the immobilisation of
the heavy metals in the matrix of the tested brick pieces as a result of oxidation during the
firing process rendering then less soluble. Overall, the results of leaching tests on the
specimens with 15% sludge show a satisfactory behavior for their adoption as a sustainable
building material.
13. CONCLUSIONS AND RECOMMENDATIONS
The studies carried out reveal that the clay material is a low activity kaolinitic clay which is
rich in silica while the sludge contained some limited quantities of heavy metals below
tolerable limits of environmental concerns. This therefore entails a rational utilization of this
sludge in a bid to avoid environmental problems. From the study it was realized that a 15 %
incorporation of sludge into the clay resulted into a composition which gave a brick
compressive strength requirement of 11.6 MPa which is above that required by the French
standard for burnt bricks. The water absorption test, water suction test and efflorescence for
this composition were within acceptable standards. The leaching tests carried out on the
bricks also revealed that very low levels of heavy metals were mobilized indicative that the
heavy metals were immobilized within the ceramic brick matrix, rendering the bricks to be
environmentally friendly. This study has clearly demonstrated a viable approach at utilizing
wastewater treatment sludge and therefore concerns on their disposal may not be a problem in
case the construction of wastewater treatment facilities for Yaoundé is envisaged.
ACKNOWLEDGEMENT
We thank the authorities of the Local Materials Promotion Authority (MIPROMALO
Yaoundé) who allowed us their facilities to carry out these tests.
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The Effect of Partial Replacement of Waste Water Treatment Sludge on The Properties of Burnt Clay
Brick
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