THE EFFECT OF PARTIAL REPLACEMENT OF WASTE WATER...

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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

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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


http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=6

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;

The Effect of Partial Replacement of Waste Water Treatment Sludge on The Properties of Burnt Clay

Brick


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:



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


Brick


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



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


Brick


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.



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


Brick


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



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)


Brick


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 (%)



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


Brick


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 (%)



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


Brick


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.



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.

REFERENCES


Brick


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