Cement Kiln Dust Stabilization of Compacted Black Cotton Soil

Cement Kiln Dust Stabilization of Compacted Black Cotton Soil G. K. Moses Department of Civil Engrg., Nigerian Defense Academy, Kaduna, Nigeria. [email protected]

A. Saminu Department of Civil Engrg., Nigerian Defense Academy, Kaduna, Nigeria. [email protected]

ABSTRACT Laboratory test was conducted on black cotton soil treated with up to 16% Cement Kiln Dust (CKD) by dry weight of soil to assess its suitability for use as road pavement material. Specimens were compacted using the energies of the British Standard Light (BSL) and West African Standard (WAS) or “intermediate”. The expansive black cotton soil classified as A-7-6 (16) or CL using the America Association of Highway and Transportation Officials (AASHTO) and Unified Soil Classification System (USCS), respectively, Soils under these groups are of poor engineering benefit. The UCS values for the untreated soil are 178 and 381kN/m2 at energy levels of BSL and WAS respectively. CKD treated black cotton soil gave a peak 7 day UCS value of 394kN/m2 and 410kN/m2 at 12% and 8% CKD content at BSL and WAS energy level respectively. These values fall short of the 1710 kN/m2 specified for base materials stabilization using OPC. And this value also fails to meet the requirement of 687–1373 kN/m2 for sub-base material. The CBR recorded an improvement in the strength from 2% and 3% for the natural soil for BSL and WAS compactive effort to attain a peak C.B.R. of 12% at 12% CKD and 16% at 12% CKD treatment for BSL and WAS compactive effort respectively. However, soil –CKD mixtures failed to meet the minimum CBR value of 30% specified for use as sub-base course material when determined at MDD and OMC. The peak resistance to loss in strength recorded for BSL and WAS were 13.2 and 16.1% (i.e. loss in strength) was attained at 16% CKD content at both energy levels. The resistance to loss in strength values all fell short of the acceptable conventional minimum of 80%.

KEYWORDS:

Cement Kiln Dust, Compaction, Durability, Unconfined Compressive Strength, California Bearing Ratio

INTRODUCTION Industrial waste disposal is constantly throwing up challenge in terms of the cost and safe disposal of these wastes that other unexplored waste are being researched upon to determine their - 825 -

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suitability as road pavement material. Problematic black cotton soil on the other hand abounds in many parts of the world such that there avoidance becomes impossible in places where the deposits are extensive. Various researchers (Ola, 1983; Balogun, 1991; Osinubi, 1995, 1999; Osinubi et al, 2009b, 2010) have attempted to stabilize the Nigerian black cotton soil with different types of stabilizers agents with varying degree of success. Cement kiln dust (CKD) is an industrial waste from cement production. The quantities and characteristics of CKD generated depend upon a number of operational factors and characteristics of the inputs to the manufacturing process. Although the relative constituent’s concentrations in CKD can vary significantly, CKD has certain physical characteristics that are relatively consistent. When managed on site in a waste pile, CKD can retain these characteristics within the pile while developing an externally weathered crust, due to absorption of moisture and subsequent cementation of dust particles on the surface of the pile (Liman, 2009). The ability of the CKD to absorb water stems from its chemically dehydrated nature, which results from the thermal treatments it receives in the system. The action of absorbing water (rehydrating) releases a significant amount of heat from non-weathered crust, a phenomenon that can be exploited in the stabilization of poor engineering material. Expansive soils are also referred to as “black cotton soil” in some parts of the world. They are so named because of their suitability for growing cotton. Black cotton soils have colors ranging from light grey to dark grey and black. Black cotton soils are confined to the semi arid regions of tropical and temperate climatic zones and are abundant where the annual evaporation exceeds the precipitation (Chen, 1975; Waen and Kirly; 2004), Balogun (1991) reported that black cotton soils occur in continuous stretches as superficial deposits and are typical of flat terrains with poor drainage. The absence of quartz in the clay mineralogy enhances the formation of fine-grained soil material, which is impermeable and waterlogged. Morin (1971) reported that the Lake Chad Basin is the only extensive lacustirne deposit of black cotton soil in Africa. The black cotton soils of North Eastern Nigeria were laid during the tertiary and quaternary periods of the Chad formation and are composed of a sequence of lacustrine and fluviatile clays and sands of Pleistocene age. These sediments (lacustrine sands, lagoonal clays, deltaic sands and clays, beach sands and gravels as well as aeolian sands) underlie the country North and East of Abakire and extend along the plains of Borno and Lake Chad and beyond (Ola, 1983). It was also reported that black cotton soils occupy an estimated area of 104 x 103 km2 in Northeastern Nigeria. The mineralogy of this soil is dominated by the presence of montimorillonite which is characterized by large volume change from wet to dry seasons and vice versa. Deposits of black cotton soil in the field show a general pattern of cracks during the day season of the year. Cracks measuring 70mm wide and over 1m deep have been observed and may extend up to 3m or more in case of high deposit (Adeniji 1991). Research work has been carried out on the improvement of geotechnical characteristics of black cotton soil with very little success using bagasse ash pozzolana ( Ijimdiya, 2009). However, no work has been done on the use of CKD treated black cotton soil as a road pavement material. The study was aimed at the evaluation of the suitability of compacted black cotton soil treated with CKD for use as a road pavement material; typical oxide composition of the cement kiln dust is shown in tables.1.

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Table 1: Basic Properties and Typical Oxide Composition of the Cement kiln dust Oxide CaO Al2O3 SiO2 Fe2O3 Mn2O3 Na2O K2O pH Gs Concentration (%) 50.81 4.71 1.92 0.002 0.001 1.35 11.2 2.22

MATERIALS AND METHODS Materials Black Cotton Soil: The soil used in this study is dark grey in colour and is known as black cotton soil, it was obtained along New-Marte road in Bayo Local Government Area of Borno State using the method of disturbed sampling. The location lies along (latitude 10° 19’N and longitude 11° 30’E). Specimens were varied with 0, 4, 8, 12 and 16% of cement kiln dust by dry weight of soil. Cement Kiln Dust: The cement kiln dust used was obtained from freshly deposited heaps of the waste at the Ashaka cement production plant located in Nafada Local Government Area of Gombe state, Nigeria. The CKD was sieved through Bs sieve No. 200 and was stored in air-tight containers before usage. Methods Index Properties: Laboratory tests were conducted to determine the index properties of the natural soil and soil – cement kiln dust mixtures in accordance with British Standards BS 1377 (1990) and BS 1924 (1990) respectively. A summary of the soil index properties is presented in Table 2.

Table 2: Engineering Properties of CKD Treated Black Cotton Soil Engineering Properties Liquid Limit, % Plastic Limit, % Plasticity Index, % Linear Shrinkage, % Percentage Passing BS No. 200 Sieve. AASHTO Classification USCS Classification Specific Gravity MDD Mg/m3 Standard Proctor West African Standard OMC% Standard Proctor West African Standard

Cement kiln dust (%) 0 67.5 22.8 44.7 15.3

4 65.0 20.6 44.4 13.3

8 72.6 19.2 53.4 13.1

12 65.0 16.9 39.1 14.0

16 64.0 14.4 54.6 13.5

85.0

83.0

85.0

81.0

83.0

A-7-6 CL 2.36

A-7-6 CL 2.37

A-7-6 CL 2.39

A-7-6 CL 2.38

A-7-6 CL 2.65

1.300 1.400

1.458 1.510

1.520 1.560

1.586 1.610

1.512 1.660

24.0 21.0

23.2 20.6

22.7 20.3

18.8 17.6

17.6 15.3

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7.2 Dark Gray Montimorillonite

-

-

-

-

Compaction All the compactions involving moisture-density relationships, CBR and UCS were carried out using energies derived from the Standard Light (BSL) and West African Standard (WAS). The BSL compactions was carried out using energy derived from a rammer of 2.5 kg mass falling through a height of 30 cm in a 1000 cm3 mould. The soil was compacted in three layers, each receiving 27 blows. The soaked CBR tests were conducted in accordance with the Nigerian General Specification (1997) which stipulates that specimens be cured dry for six days, then soaked for 24 hours before testing. The CBR compaction involved the use of the same rammer weight and drop height with each layer receiving 62 blows in a 2360 cm3 mould. The WAS compaction, was carried out using energy derived from a rammer of 4.5 kg mass falling through a height of 45 cm in a 1000 cm3 mould. The soil was compacted in five layers, each layer receiving 10 blows. For the CBR compaction, the same rammer weight and drop height was adopted with each layer receiving 30 blows in a 2360 cm3 mould. The UCS test specimen was compacted at BSL and WAS energy levels. Specimens were cured for 7, 14 and 28 days before testing.

RESULTS AND DICUSSION Index Properties: Results of tests carried out on the natural soil are summarized in Table.1. The soil is classified under the A – 7 – 6 subgroup of the AASHTO classification system. Liquid limit and plasticity index values of 67.5 % and 44.7 %, respectively, suggest that the soil is highly plastic. Thus, from the results obtained, the soil falls below the standard recommended for most geotechnical works (Butcher and Sailie, 1984).

Maximum Dry Density The MDD for the BSL and WAS compactive effort is in conformity with the trend of decreasing OMC with increasing MDD. This is as a result of CKD occupying the void within the soil matrix and in addition, the flocculation and agglomeration of the clay particle due to exchange of ions (Osinubi, 2000 a; Moses, 2008; Oriola and Moses, 2010,). While the final decrease in MDD for BSL compactive effort can be attributed to CKD, a low specific gravity material replacing the soil material which has a high specific gravity (Osinubi and Stephen 2007).

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Maximum dry density (Mg/m3)

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1.7

1.65 1.6

1.55

BSL

1.5

WA

1.45 1.4

1.35 1.3 1.25 0

4

8

12

16

CKD Content (%)

Figure 1: Variation of Maximum Dry Density With CKD

Optimum Moisture Content

Optimum Moisture Content (%)

For specimens compacted at the British standard light and West African Standard energy levels, a decrease in OMC was recorded this is probably due to self – desiccation in which all the water was used, resulting in low hydration. When no water movement to or from cement – paste is permitted, the water is used up in the hydration reaction, until too little is left to saturate the solid surfaces and hence the relative humidity within the paste decreases. The process described above might have affected the reaction mechanism of CKD treated black cotton soil (Osinubi and Stephen 2007, Moses 2008). 27 25 23 21 19 17 15 13

BSL WA

0

4

8

12

16

CKD Content (%)

Figure 2: Variation of Optimum Moisture Content With CKD

Strength Characteristics Unconfined compressive strength The variation of unconfined compressive strength (UCS) with slag content for soil –CKD mixtures at 7, 14 and 28 days curing periods are shown in Figs. 3 - 5. Generally, the UCS of the soil – CKD – mixtures increased up to 12% CKD treatment and thereafter decreased. The 7 days UCS of the untreated black cotton soil improved from a value of 178kN/m2 and 381kN/m2 to a peak value of 381kN/m2 and 410kN/m2 at 12% CKD and 8% CKD treatment level at both BSL and WAS energy levels The peak blend of CKD treated soil was attained at 12% CKD content at - 829 -

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7 days unconfined compressive strength (kN/m2)

BSL compactive effort with a peak 7 day UCS value of 394 kN/m2. This value falls short of 1710 kN/m2 specified by TRRL (1977) for base materials stabilization using OPC. Furthermore, this value fails to meet the requirement of 687–1373 kN/m2 for sub-base as specified by Ingles and Metcalf (1972). 500 BSL

400

WAS

300 200 100 0

4

8

12

16

CKD Content (%)

Figure 3: Variation of of unconfined compressive strength (7 days curing) with CKD content for soil-CKD mixtures


The increase in UCS values could be attributed to ion exchange at the surface of clay particles. The Ca2+ in the additives reacted with the lower valence metallic ions in the clay microstructure which resulted in agglomeration and flocculation of the clay particles. The UCS of soil - CKD mixture containing 12 % CKD content as expected increased with curing period as shown in Fig. 4-5. The gain in strength of specimens with age was due primarily to the long-term hydration reaction that resulted in the formation of cementitious compounds. 600 500

BSL

400

WAS

300 200 100 0 0

4

8

12

16

CKD Content (%)


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700 600 500

BSL

400

WAS

300 200 100 0 0

4

8

12

16

CKD Content (%)


California bearing ratio The variation of California bearing ratio (CBR) with CKD content for soil – CKD mixtures is shown in Fig. 6. Generally, CBR increased with higher CKD content. The reason for the improvement in the strength from 2% and 3% for the natural soil at BSL and WAS compactive effort to 12% at 12% CKD and 16% at 12% CKD treatment for BSL and WAS compactive effort respectively. This could be due to the presence of adequate amounts of calcium required for the formation of calcium silicate hydrate (CSH), which is the major compound for strength gain. A CBR value of 180% is recommended by (BS, 1990b) which is expected to be attained in the laboratory for cement-stabilized material to be constructed by the mix-in-place method. However, soil –CKD mixtures failed to meet the minimum CBR value of 30% specified by (BS 1990b) for materials suitable for use as base course material when determined at MDD and OMC. Furthermore, none of the energy levels produced satisfactory values for base, sub-base and subbase material.

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California Bearing Ratio (%)

8 7 6 BSL

5 WAS

4 3 2 1 0 0

4

8

12

16

CKD Content (%)

Figure 6: Variation of soaked California bearing ratio with CKD content for soil-CKD mixtures

Durability Compressive strength is employed as an evaluation criterion to ensure that the stabilized material does not fail under adverse field conditions. In order to simulate some of the worst conditions that can be experienced in the field for any soil to be used for engineering purposes, cured specimen were immersed in water before testing. The value obtained under this laboratory simulated field condition are analysis with the 14 days cured specimen to obtain the percentage resistance to loss in strength of the stabilized material as recommend for tropical countries (Ola, 1974). The peak resistance to loss in strength recorded for BSL and WAS were 13.2 and 16.1% (i.e. loss in strength) was attained at 16% CKD content. This resistance to loss in strength falls short of the acceptable conventional minimum of 80% (Ola, 1974).

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Resistance to loss in Strength (%)

18 16 BSL

14

WAS

12 10 8 6 4 0

4

8

12

16

CKD Content (%)

Figure 7: Variation of resistance to loss of strength of soil treated with CKD content for soil-CKD

CONCLUSIONS The natural black cotton soil was classified as A – 7 – 6 or CL in the AASHTO and Unified Soil Classification System (USCS), respectively. Soils under these groups are of poor engineering benefit. Natural soil treated with CKD gave a peak 7 day UCS value of 381kN/m2 and 410kN/m2 at 12% and 8% CKD content at BSL and WAS energy level respectively. This values fall short of 1710 kN/m2 specified by TRRL (1977) for base materials stabilization using OPC. And this value also fails to meet the requirement of 687–1373 kN/m2 for sub-base as specified by Ingles and Metcalf (1972). Peak C.B.R values of 5 and 7% were obtained at 12% CKD content at the energy levels of BSL and WAS. These values fail to satisfy the specification for base or sub-base materials as recommended by the Nigerian General Specifications (1997). The durability assessments of sample also recorded values that fail to meet the acceptable limits. Finally, cement kiln dust treated black cotton soil failed to record desired result. Therefore, it is not recommended for use as a single stabilizing agent for road pavements.

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35. Oriola, F. and Moses, G. (2010) “Groundnut Shell Ash Stabilization of Black Cotton Soil” Electronic Journalof Geotechnical Engineering. Vol. 15, Bund, E 415-428. 36. Oriola, F.O.P., Moses, G., (2011) Compacted black cotton soil treated with cement kiln dust as hydraulic barrier material. American Journal of Scientific and Industrial Research. Vol. 2 Issue 4, pp.521-530 37. Rizkallah, V. (1982) “Stabilization of difficult soils in developing countries’. Proc. of 12th Int. Conf. on Soil Mech. and Found. Engineering, Vol. II, Rio De Janeiro, 301 – 304. 38. Sambhandharaksa, S. and Moh. Z. C. (1971). “Effects of salt content on thixotropic behaviour of a compacted clay”. Proc. of the 1st Australia New Zealand Conf. On Geomechanics, Malbourne Vol. 1. 39. So, El – Kon (1992) “Research on the optimum secondary additives to granulated clay – stabilized soils.” In: T. Mise et al., (eds.) Soil Improvement, Current Japenese Materials Research, Vol. 9. Elsevier Science Publishers, London and New York. 40. TRRL (1977) “A guide to the structural design of Bitumen surfaced Roads in tropical and Sub – Tropical countries” Transport and Road Research Laboratory, Road Note 31, H. M. S. 0. London. 41. Unified Soil Classification System Based on Wagner, A.A. (1957) Proceedings of the International Conference SMFE, London, Vol. 1. Butterworth & Co. 42. Warren, K.W. And Kirby, T.M. (2004) “Expansive Clay Soil A Wide BSLread And Costly Geohazard”, Geostra, Geoinstitute Of The American Society Of Civil Engineers 43. Watson, J. (1991). Highway construction and maintenance. Longman Group, U.K. 44. Yoder, E. J. and Witczak, M. W. (1975). Principles of Pavement Design. John Wiley and Sons. Inc. New York, 300 – 321 aboundone

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