Improving the Strength Properties of Afari and Mfensi Clays by Chemical Stabilization

Improving the Strength Properties of Afari and Mfensi Clays by Chemical Stabilization

Robert Amoanyi1,a, P. S. Kwawukume2,b and Francis Y Momade3,c

1,2Department of Industrial Art (Ceramics Section) 3Department of Materials Engineering

Kwame Nkrumah University of Science and Technology, Kumasi, Ghana

[email protected], [email protected], [email protected]

[Date received: 1 June 2011. Date accepted: 30 November 2012]

Keywords: Clays, Physical and chemical properties, Compressive strength, Water absorption, Chemical stabilization

Abstract. Physical and chemical studies were conducted on Afari and Mfensi clays in Atwima Nwabiagya District in Ashanti Region of Ghana, with the view of improving their strength properties by chemical stabilization with cocoa pod ash (CPA) and lime as chemical stabilizers. The idea was to produce stabilized clay brick without firing as an improved building material for the rural housing in areas where the materials exist and beyond. The results revealed an improvement in both dry and wet compressive strengths with the additions of 10% to 15% lime and CPA. The maximum dry compressive strength of 2.07N/mm2 and 5.85N/mm2 and wet compressive strength of 0.91N/mm2 and 2.67N/mm2 respectively were recorded for Afari and Mfensi clays. The water absorption also reduced from 100% to 27.59% and 17.78% respectively for Afari and Mfensi clays. Although there were decreases in wet compressive strength on soaking the specimens in water, the stabilized bricks did not disintegrate after 28 days of soaking. Moreover, the stabilized clay bricks showed good durability behaviour and did not disintegrate when exposed in the open air for two years.

Introduction

Clay stabilization is the process of improving the engineering properties of clay soils by binding the soil particles together so that a rigid, non-dispersible mass is obtained with high load-bearing strength and thus making it more stable and durable and resistant to eroding in the presence of excessive moisture. Stabilization of clay components by chemical additives finds broad application in various construction activities [1]. It is an outgrowth of ancient practice which has been modified by laboratory and field tests to fulfil a variety of stabilization requirements. This is due to the fact that many clay soils cannot be used as engineering materials in their own natural state [2]. Clay is usually the unstable part of soil in the presence of excessive moisture. However, it is the most reactive component of soil due to its fineness of particles [3]. Afari and Mfensi clay deposits in the Atwima Nwabiagya District in the Ashanti Region of Ghana are among the various types of clays found in commercial quantities in every district of Ghana [4]. Since the establishment of Kwame Nkrumah University of Science and Technology, Kumasi, the Ceramics, Sculpture, Design and Foundation sections as well as Department of Integrated Rural Art and Industry, have depended solely on these clay soils for teaching, research and the fabrication of ceramic products. Additionally, there are also a number of individuals who have established small-scale industries in Afari and Mfensi communities, producing pottery wares such as water coolers, grinding bowls, palm wine pots, etc as well as burnt bricks using these clays as their main raw material. Aside the

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numerous uses of these clays, it appears little has been done to determine their response to stabilization with available chemical additives for making stabilized clay bricks for building purposes especially in their rural catchment communities. Although a lot of researches have been conducted on clay stabilization with very encouraging results involving the use of chemical stabilizers such as lime, cement, aluminium sulphate, asphalt and sodium hydroxide among others [2, 5, 6, 7, 8, 9] not much has been reported on the use of totally local ashes and lime in stabilisation. With the exception of lime, the above mentioned stabilizers or additives are not readily available locally; those readily available are costly which makes their use on a commercial level unacceptable due to cost implications. There is therefore the need to search for more locally available options of stabilizers or additives which can lead to the development of durable and low cost building materials for these communities. Cocoa pod husk is available in all cocoa growing areas of Ghana. It is estimated that Ghana can access over 50,000 tonnes of potash annually with a market value of some millions of dollars from the cocoa pod husks thrown away as agricultural wastes after seasonal harvesting. This potash (organic potash) from ashes of agricultural wastes has advantage over mined potash, especially for the food industry, which is totally free from arsenic [10]. The aim of this study is to investigate the possible use of ash from cocoa pod husk usually left over after seasonal harvesting and local lime as local stabilizers. Furthermore, it is the desire of this work to determine the stabilization response of Afari and Mfensi clays with the chemical stabilizers (cocoa pod ash and lime) in terms of strength since due to high cost of energy, there is now the growing interest in stabilised earth building materials. Materials and Methods

Materials used in this research were Afari and Mfensi clays collected randomly at the deposit sites, dried at 105oC for 24 hours and reduced to fine particle sizes through the use of cone crusher and vibratory mill. The clays were tested for particle size distribution, Atterberg limits (liquid limit, plastic limit and plasticity index), drying shrinkage and volumetric shrinkage to determine their characteristics as engineering materials suitable for stabilization. Drying shrinkage is the decrease in size that usually occurs when a shaped product (clay ware or ceramic ware) is dried. It is usually expressed as a linear percentage contraction from the wet to the dry state. Volumetric shrinkage is the decrease in volume that usually occurs when a shaped product (clay ware or ceramic ware) is dried. It is the contraction which occurs in all the dimensions of the shaped product from the wet to the dried state. The methods employed in the execution of the above mentioned tests were in accordance with the British Standards 1377 [11]. The chemical stabilizers namely lime and cocoa pod husk were separately fired to 600oC then reduced to fine powders and tested for chemical analysis as well as fluorescence spectrometry on Spectro X-Lab 2000 Polarized Energy Dispersive X- Ray Fluorescence Spectrometer (EDXRF) equipment at the X-ray fluorescence laboratory of the Geological Survey Department, Accra, Ghana

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Table 1 Percentage composition of materials weighed for Afari clay samples

Composition Afari clay

(%) Lime (%)

Cocoa Pod Ash (%)

A0 100 0 0 A1 95 0 5 A2 90 0 10 A3 85 0 15 A4 95 5 0 A5 90 5 5 A6 85 5 10 A7 80 5 15 A8 90 10 0 A9 85 10 5

A10 80 10 10 A11 75 10 15 A12 85 15 0 A13 80 15 5 A14 75 15 10 A15 70 15 15

Table 2 Percentage composition of materials weighed for Mfensi clay samples

Composition Mfensi clay

(%) Lime (%)

Cocoa Pod Ash (%)

M0 100 0 0 M1 95 0 5 M2 90 0 10 M3 85 0 15 M4 95 5 0 M5 90 5 5 M6 85 5 10 M7 80 5 15 M8 90 10 0 M9 85 10 5

M10 80 10 10 M11 75 10 15 M16 70 10 20 M12 85 15 0 M13 80 15 5 M14 75 15 10 M15 70 15 15 M17 65 15 20

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Fabrication of test pieces: The materials were measured in 1500g batches each for both clays based on the recipes shown in Tables 1 and 2. The constituents were mixed to an even consistency before manual moulding in a steel mould measuring 50mm x 50mm x 50mm that was designed for this work. Approximately 25 blows of uniform pressure were applied to each test piece whilst in the mould. The excess material was cut off using running knife across the top of the mould. Ten test pieces were made for each composition and labelled accordingly. The test pieces were removed from the mould after each successful moulding.

The freshly made test pieces were kept in polythene bags for a week and later dried in an oven for 24 hours at the temperature of 60oC and later cooled. Subsequently, some the test pieces were kept in water for 28days and weights were taken weekly (7th day, 14th day, 21st day and 28th day) before the wet and dry compressive strength tests were performed in accordance to BS 3921 [12]

Results and Discussion

Particle size distribution: The results of the physical tests of Afari and Mfensi clays are presented in Table 3 which shows that both clay soils have clay fractions of 48% and 37% for Afari clay and Mfensi clay respectively. This helps in the development of plasticity in the soil for moulding and retention of strength when air-dried. The silt fraction in Afari and Mfensi clays are 27% and 43% respectively. The sand fractions are 25% and 20% for the total Afari and Mfensi clay soils respectively. Silt and sand particles are considered as non-plastic materials. In accordance with these results where Afari clay contains slightly more clay fraction (48%) coupled with less silt content (27%) as compared to Mfensi clay with 37% clay fraction and 43% silt, Afari clay shrinks slightly more than Mfensi clay as shown in Table 3. Afari and Mfensi clay could be classified as sandy-clay and silty-clay respectively and both clays could also be considered as fine-grained soils

that are ideal for stabilisation.

Table 3 Physical properties of Afari and Mfensi clay samples

Sample Colour

Drying Shrinkage (%)

Volumetric Shrinkage (%)

Atterberg Limits Test (%) Particle size distribution (%)

Liquid Limit (LL)

Plastic Limit (PL)

Plasticity Index (PI) LL-PL= PI

Clay <2µm

Silt 2µm-60µm

Sand 60µm-2000µm

Afari Clay

Yellowish orange

9.8 27.42 73.40 26.92 46.48 48 27 25

Mfensi Clay

Greenish grey

7.4 21.89 43.34 20.80 22.54 37 43 20

Atterberg limits (liquid limit, plastic limit and plasticity index) of Afari and Mfensi clays

The results shown in Table 3 indicate that Afari clay has liquid limit of 73.40% while Mfensi clay has 43.34% and plastic limit results of Afari clay (26.92%) and Mfensi clay (20.80%) respectively. The difference in liquid limit and plastic limit gives the plasticity index value of 46.48% for Afari clay and plasticity index value of 22.54% for Mfensi clay respectively. Gogo [13] pointed out that plasticity characteristics play an important role in stabilization study which gives an indication of the approximate water content which is likely to give the optimum workability during mixing. This was proven during the fabrication of the test pieces where the amount of water for optimum workability used during mixing was between 25% and 45%. Percentage drying and volumetric shrinkages of Afari and Mfensi clays: From Table 3 the percentage drying shrinkage of Afari clay is 9.4% and Mfensi clay is 7.4% and percentage volumetric shrinkage of Afari clay is 27.42% and Mfensi clay is 21.89%. Though Afari clay shrinks slightly more than Mfensi clay, both clays have low percentage drying and volumetric shrinkages in

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their dried state. These results are similar to those of Dodd and Murfin [14] and Amonoo-Neizer [15] which show that the drying and volumetric shrinkages of products of dimensional accuracy such as bricks, must be low. The drying shrinkage values of both Afari and Mfensi clays are almost one-third of their volumetric shrinkage values. This observation is confirmed by Worrall [16] that linear shrinkage is approximately one-third of volumetric shrinkage for an isotropic specimen, which is a body that shrinks equally in all directions. From the observation of these results and assertion by Worrall [16] it may be concluded that both clays shrink almost equally in all directions that gives the values of their drying shrinkages almost one-third of their volumetric shrinkages and is good for brick production. From the observation from these physical properties of both Afari and Mfensi clays and the assertion by Worrall [16], Dodd and Murfin [14] and Amonoo-Neizer [15], it may be concluded that both clays are good engineering materials for stabilization by chemical stabilizers. Table 4 Chemical compositions (wt %) of Afari and Mfensi clays and cocoa pod ash

Element Afari clay Mfensi clay Cocoa pod ash

SiO2 48.88 58.62 8.05

Al2O3 26.56 23.44 2.28

Fe2O3 6.66 3.63 0.89

CaO 0.24 0.14 8.43

MnO 0.01 0.02 0.10

MgO 1.61 1.41 5.16

Na2O 1.73 2.06 0.44

K2O 0.13 1.28 37.39

TiO2 0.79 0.9 0.14

P2O5 0.06 0.13 2.33

SO3 0.17 0.18 2.09

LOI 13.16 8.18 32.71

Total 100 100 100

Chemical composition (wt %) of Afari and Mfensi clays and cocoa pod ash: In considering the amount of SiO2 (Afari clay - 48.88% and Mfensi clay - 58.62%), Al2O3 (Afari clay - 23.44% and Mfensi clay - 23.44%) and the alkaline oxides (Afari clay – 3.72% and Mfensi clay - 4.91%) in these clay soils as shown in Table 4, the clays show the typical characteristics of kaolinitic clays [16]. Furthermore, the total silica+alumina+iron oxide in the clays is not less than 70%, which is within the Indian specification as shown in Table 5 for clays that can produce pozzolanas [17].

International Journal of Engineering Research in Africa Vol. 8 5

As shown in Table 4, cocoa pod ash has relatively high amount of potassium oxide (K2O) - 37.39% and appreciable amount of calcium oxide (CaO) - 8.43%. These are the expected alkali in ash to react with the clay soils to form a cementing matrix. The high loss on ignition (LOI) in the cocoa pod ash (32%) is due to the hydroscopic nature of ash. Table 5 Chemical composition of clay suitable for use in calcined clay pozzolanas [17]

Constituents Contents by weight Silica + Alumina + Iron Oxide Silica Calcium Oxide Magnesium Oxide Sulphur trioxide Water soluble alkali Water soluble material Loss on ignition

Not less than 70% Not less than 49% Not more than 10% Not more than 3% Not more than 3% Not more than 0.1% Not more than 1% Not more than 10%

Dry compressive strength of test pieces: The results of the dry compressive strength test conducted on Afari and Mfensi clays test pieces with variations in lime and cocoa pod ash (CPA) are shown in Figures 1 – 4.

A3

A2

A1

A0

M0

M3

M2M1

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 5 10 15 20% CPA

Co

mp

ressiv

e s

tre

ng

th (

N/m

m2

)

Afari

Mfensi

Figure 1 Compressive strength of Afari and Mfensi clays against percentage variation

of cocoa pod ash (CPA) with no lime addition

From Figure 1, it can be seen that the strength of Mfensi clay test pieces (M) increases to a maximum value of 1.36N/mm2 at 10% CPA, after which the strength falls off with further increase in CPA. The strength of Afari clay test pieces also increases to a maximum of 1.12N/mm2 at 5% CPA, after which it decreases subsequently with further increase in CPA. The compressive strength of Mfensi clay test pieces with varying additions of CPA is higher than Afari clay test pieces. This is due to the characteristic nature of the clays.

6 International Journal of Engineering Research in Africa Vol. 8

A7

A6

A5

A4

M4

M7

M6

M5

0

0.5

1

1.5

2

2.5

3

0 5 10 15 20% CPA

Co

mp

ress

ive

str

en

gth

(N

/mm

2)

Afari

Mfensi

Figure 2 Compressive strength of Afari and Mfensi clays with 5% lime against

percentage variation of cocoa pod ash (CPA

It may be noted from Figure 2 that the compressive strength of Mfensi clay test pieces increased with 5% lime and 10% CPA addition. However, with further increase in CPA to 15% a decrease in strength was observed. A similar trend is observed with Afari clay test pieces. In comparison with the test pieces of both clays, Mfensi clay test pieces have a relatively higher compressive strength than Afari with 5% lime plus variations of CPA. There is also an improvement in the strength of both clay test pieces when 5% lime and 5% CPA were added to the clays as in Figure 2 than with no lime addition as in Figure 1. As lime was increased to 10% plus percentage variations of CPA as in Figure 3, there was a relatively significant improvement in the compressive strength of test pieces of both clays. Especially with Mfensi clay test pieces, there is a significant increase in strength as the CPA is increased to 15% giving a compressive strength value of 5.85 N/mm2. However, with an increase in CPA to 20% a decrease in strength is noticed. This could be attributed to cation exchange reaction between the additives and the clay leading to partial deflocculating of the clay causing decrease in agglomeration of the particles hence lower strength as the % K2O increases. Additionally, the low silica content in the CPA contributed to low cementing properties since for pozzolanic properties high silica content is necessary [18]. The compressive strength of 5.85 N/mm2 was the highest value attained during the study though not relatively very high as was expected. It is however within the specified values for compressive strength of between 2 and 5N/mm2 given by McHenry [19] and ILO/UNIDO [20], and the minimum British Standard requirement of 2.85N/mm2 for concrete blocks and fired clay bricks or all building bricks [12, 21].

International Journal of Engineering Research in Africa Vol. 8 7

A11

A10A9

A8

M16

M8

M11

M10

M9

0

1

2

3

4

5

6

7

0 5 10 15 20 25% CPA

Co

mp

ressiv

e s

tre

ng

th (

N/m

m2

)

Afari

Mfensi

Figure 3 Compressive strength of Afari and Mfensi clays with 10% lime against percentage

variation of cocoa pod ash (CPA)

A15A14A13

A12

M17

M12

M15

M14

M13

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 5 10 15 20 25% CPA

Co

mp

ressiv

e s

tre

ng

th (

N/m

m2

)

Afari

Mfensi

Figure 4 Compressive strength of Afari and Mfensi clays with 15% lime against percentage

variation of cocoa pod ash (CPA)

It can be observed in Figure 4 that, both clays (Afari + CPA and Mfensi + CPA) have similar increasing trend up to a maximum at 10% CPA, after which the strength falls in Afari + CPA with an increase in CPA. However, with Mfensi + CPA sample bricks; there was an increase in strength up to a maximum of 4.63N/mm2 at 15% CPA then a decrease with 20% CPA addition. This could be attributed to cation exchange reaction between the additives and the clay leading to partial deflocculating of the clay causing decrease in agglomeration of the particles hence lower strength as the % K2O increases. Additionally, the low silica content in the CPA could have contributed to low cementing properties since for pozzolanic properties high silica content is very necessary [18].

8 International Journal of Engineering Research in Africa Vol. 8

A7

A6

A5

M7

M6

M5

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 5 10 15 20% CPA

Co

mp

ressiv

e s

tre

ng

th (

N/m

m2

)

Afari

Mfensi

Figure 5 Wet compressive strength of Afari and Mfensi clays with 5% lime against percentage

variation of CPA

Wet compressive strength of test pieces (clay + lime + CPA): Wet compressive strength test were performed on the Afari and Mfensi clay test pieces immediately after soaking for 28 days in water. Data on the wet compressive strength of the Afari and Mfensi clay test pieces at various amounts of lime and cocoa pod husk ash (CPA) additions after 28 days of soaking in water are shown in Figures 5 - 7. The wet compressive tests could not be performed on the specimens with only 5% lime and no addition of CPA. This was due to the flaking of the edges of the test pieces when removed after 28days soaking in water. Figure 5 shows that the wet compressive strength for both clays occurs at 10% CPA. However, Mfensi clay has higher compressive strength than the Afari. This may be explained by the fact that Afari clay absorbs more water than Mfensi which weakens the pores and therefore causes reduction in the wet compressive strength. Figures 6 and 7 exhibit similar trend with Figure 5 however with the maximum wet compressive strengths occurring at 15% CPA for Mfensi clay in both Figures 6 and 7, while that for Afari clay occurring at 10% CPA in the two figures.

International Journal of Engineering Research in Africa Vol. 8 9

A9 A10A11

M16

M9

M10

M11

0

0.5

1

1.5

2

2.5

3

0 5 10 15 20 25% CPA

Co

mp

ressiv

e s

tre

ng

th (

N/m

m2

)

Afari

Mfensi

Figure 6 Wet compressive strength of Afari and Mfensi clays with 10% lime against

percentage

Variation of CPA

A13A14

A15

M17

M13

M14

M15

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 5 10 15 20 25% CPA

Co

mp

ressiv

e s

tre

ng

th (

N/m

m2

)

Afari

Mfensi

Figure 7 Wet compressive strength of Afari and Mfensi clays with 15% lime against

percentage

Variation of CPA

The following statements can be made for Figures 5 – 7:

1. Afari and Mfensi clay test pieces with no additives disintegrated in the water within the period of an hour. Afari and Mfensi clay test pieces with the CPA as the only additive also disintegrated in about a week of soaking in water. Wet compressive strength test could not be performed on these test pieces.

2. Afari and Mfensi clay test pieces with lime as the only additive were able to maintain their shapes in water for the 28-day period of soaking without disintegrating, but some damages were noticed at the edges and some surfaces of the test pieces. Thus, the edges of the test pieces were flaking off hence no wet compressive strength tests were performed on these test pieces.

10 International Journal of Engineering Research in Africa Vol. 8

3. Although there is a drastic reduction in wet compressive strength as compared to the dry compressive of all the compositions of both Afari and Mfensi clays test pieces (Figures 1, 2, 3, 4, and Figures 5, 6, 7), wet compressive strength of Mfensi clay test pieces is higher than Afari.

Water absorption of test pieces (clay + lime + CPA): Water absorption tests were performed on Afari and Mfensi clays test pieces with percentage variation of lime and cocoa pod ash (CPA) during and immediately after 28days of soaking in water. The results are shown in Figures 8 – 10.

A5A6 A7

M5 M6M7

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25% CPA

% W

ate

r a

bso

rptio

n

Afari

Mfensi

Figure 8 Percentage water absorption of Afari and Mfensi clays with 5% lime against

percentage

Variation of CPA

In Figures 8 to 10, due to the flaking of the edges of the test pieces with 5% lime as the only additive, no values were obtained for 5% lime plus no addition of CPA. In summary, a comparison of the results of percentage water absorption of Afari and Mfensi clays test pieces with varying amounts of the additives (lime, CPA and lime plus CPA) in all compositions showed in Figures 8 to 10, the following can be deduced:

International Journal of Engineering Research in Africa Vol. 8 11

A9A10

A11

M16

M9M10

M11

0

5

10

15

20

25

30

35

0 5 10 15 20 25% CPA

% W

ate

r a

bso

rptio

n

Afari

Mfensi

Figure 9 Percentage water absorption of Afari and Mfensi clays with 10% lime against

percentage variation of CPA

Figure 10 Percentage water absorption of Afari and Mfensi clays with 15% lime against

percentage variation of CPA

1. Both Afari and Mfensi clay test pieces were at or close to full saturation of soaking after seven days. Thus the weights of the test pieces after seven days of soaking were almost the same as the weight after 14, 21 and 28 days respectively.

2. Afari and Mfensi clay test pieces with no additives disintegrated in the water within the period of an hour. Afari and Mfensi clay test pieces with the ash (CPA) as the only additive also disintegrated in about a week of soaking in water. Water absorption test could not be performed on these test pieces.

3. Afari and Mfensi clay test pieces with lime as the only additive were able to maintain their shapes in water for the 28-day period of soaking without disintegrating, but some damages were noticed at the edges and some surfaces of the test pieces.

4. Water absorption in both clays reduced as the amounts of additives were increased. The decrease in water absorption over time was significantly low.

12 International Journal of Engineering Research in Africa Vol. 8

5. The water absorption values of treated Afari clay test pieces were higher between 27 - 36% when compared with treated Mfensi clay test pieces which were in the range of 17 - 22%. Hence Afari clay test pieces absorb more water than Mfensi clay test pieces.

Durability test: Five test pieces each of both clay soils were kept in the open for natural weathering for two years. Afari and Mfensi clay test pieces with CPA as the only additive which were kept in the open for natural weathering disintegrated when exposed to the weather after two to three times of rainfall. Afari and Mfensi clay test pieces with 5%, 10% and 15% lime as the only additive which were also kept in the open for natural weathering did not disintegrate, but the surfaces and the edges seemed to be flaking off due to the brittle nature of these test pieces. Generally, Afari and Mfensi clays test pieces treated with both lime (5%, 10% and 15%) and CPA (5%, 10% and 15%) appeared to be of good quality and were able to maintain their shape during the 28-day period in the water without distortions. There was only slight change in colour. The surfaces were free from cracks. It can be concluded that Mfensi clay responded well when treated with lime and CPA.

Chemical reactions: According to Little [3], clay soil is the most chemically active and reactive soil due to its fineness particles and it is with this the chemical stabilizers (lime plus cocoa pod ash) react. From this reaction, calcium ions in lime react with the amorphous silica and alumina in the clays to form calcium silicate and calcium aluminate. Moreover, the potassium ions in the ash also react with the amorphous silica and alumina in the clays to form potassium silicate and potassium aluminate. These compounds have some cementitious properties which improve the strength and durability of the clay soil. The binding reaction is illustrated by the following equations according to Little [3]:

Ca++ + OH- + Soluble Clay Silicon Î Calcium Silicate Hydrate (CSH) Ca++ + OH- + Soluble Clay Aluminium Î Calcium Aluminate Hydrate (CAH) He further stated that the cemented products are calcium-silicate hydrates and calcium-aluminate-hydrates. These are essentially the same hydrates that form during the hydration of Portland cement. It is therefore possible that the results of the durability test were as a result of hydration effect brought about by the chemical reaction between the clay and the chemical additives of the CPA and the lime used. Moreover, Little [3], advises that for lime stabilisation to be successful, sufficient lime must be made available to provide for the initial soil modification, to maintain a high pH environment to liberate the soluble silicon and aluminium, and to provide free calcium to form the pozzolanic reactions.

International Journal of Engineering Research in Africa Vol. 8 13

Conclusion

Chemical stabilization applied to Afari and Mfensi clays using lime plus cocoa pod ash as stabilizers has shown a remarkable improvement in strength and water absorption. With the addition of 10 - 15% lime and 10 - 15% cocoa pod ash to both Afari and Mfensi clays, dry compressive strength increased from 0.8 N/mm2 and 0.91 N/mm2 to 2.07 N/mm2 and 5.85 N/mm2 respectively. Wet compressive strength also increased from 0 N/mm2 on both Afari and Mfensi clays to 0.91 N/mm2 and 2.67 N/mm2 respectively. In comparing Afari and Mfensi clays in terms of strength and water absorption, Mfensi clay responded well than Afari clay. On the whole, the study has shown that Afari and Mfensi clays in the Atwima Nwabiagya District of Ghana can be successfully stabilized with cocoa pod ash and lime to produce unfired bricks with improved strength and water resistance and can withstand the weather conditions in the country.

References

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[11] BS 1377: 1990, Standard Methods of Soils Testing for Civil Engineering Purposes, British Standard Institution, London. (1990).

[12] BS 3921: 1985, British Standards Specification for Clay Bricks, British Standard Institution, London. (1985).

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[14] A. Dodd and D. Murfin, Dictionary of Ceramics, Institute of Metals, London, 1994.

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[17] IS 1344: 1981, Indian Standards Specification for pozolana clays, Indian Standards Institution (1981).

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Improving the Strength Properties of Afari and Mfensi Clays by ChemicalStabilization

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