Stabilization of Black Cotton Soil With Locust Bean Waste Ash
Chapter One
ย Aim and Objectives of theย Study
This study was aimed at establishing the effect of locust bean waste ash on cement modified black cotton soil. This was achieved through the following specific objectives:
- Determination of the properties of the natural properties
- Modification of black cotton soil using known quantities of cement and locust bean waste ash as admixture when compacted with the British Standard light (BSL), West African Standard (WAS) and British Standard heavy (BSH) conpaction
- Evaluation of the effect of locust bean waste ash on the cement modified black cotton soil using particle size distribution, Atterberg limits, compaction tests and shear strength
- Determination of the optimum mix ratio of cement โ locust bean waste ash for optimum workability of black cotton
CHAPTER TWO
LITERATURE REVIEW
Soil Modification /Stabilization
Generally, geotechnical structures are to be founded on good and sound engineering soil in order for them to attain their design life span. If these structure are founded on soil with low bearing capacity, they are likely to fail either during or after construction, with or without application of wheel load on them. The black cotton soil is an expansive soil with low bearing capacity, has the ability to absorb and dissipate water with subsequent change in volume. Construction of any structure on this typeย of soil requires either replacement of the soil by importing a better foreign one or by addition of chemical(s) that will improve the desired properties of the soil. But if the constructionย involvesย aย largeย areaย ofย landย likeย roadย construction,ย replacementย ofย soilย by importingย newย materialsย orย avoidingย themย isย impossibleย andย theย soilย willย thereforeย have to be stabilized in-situ (Osinubi,ย 1995).
Well built and maintained roads play major role in the development of a nation. Sub-grade soil form the integral part of the road pavement structure as it provides the support to the pavement from beneath. Therefore, the knowledge of properties of sub- grade soil are very important in the design of road pavement as well as other engineering structures. The main function of the sub-grade is to give adequate support to the pavement and for this, the sub-grade should posses sufficient stability under adverse climate and loading condition. If the weak sub-grade is stabilized, the required crust (outer layer) thickness will be less, rutting is restricted resulting in less repair and overall economy. Basically, there are three majors ways of modifying/stabilizing soils for engineering purposes. These are mechanical, geosynthetic and chemical modification.ย Modificationย isย restrictedย toย clayeyย soilsย ofย theย AASHTOย A-4,ย A-5,ย A-6, and A-7 (Office of geotechnical Engineering,ย 2008).
Modification occurs as a result of calcium cations supplied by modifier replacing the cations present on the surface of clay minerals, promoted by the highย pH environmentย ofย theย modifierย โย waterย system.ย Thusย altered,ย theย clayย surfaceย mineralogy results in plasticity reduction, reduction in moisture holding capacity, swell reduction, improved stability and the ability to construct working platform as benefit (National Lime Association,ย 2001).
Mechanical modification /ย stabilization
Mechanical stabilization is the process of altering soil properties by changing the gradation through mixing with other soil, densifying the soil using compactive efforts, or undercutting the existing soil and replacing them with granular material to improve the soil engineering properties of strength, permeability and compressibility. An existing soil may have poor engineering properties perhaps because of excess clay, silt or fine sand. If a suitable soil is located within a reasonable haul distance, blending the soil together could effect an improvement in the existing soil.
A common remedial procedure for wet and soft grade is to cover it with granular materials or to partially remove and replace the wet sub-grade with a granular material to a predetermined depth below the grade line. The compacted granular layers distribute the wheel loads over a wider area and serve as a working platform (Thompson, 1977).
To provide a firm working platform with granular material, the following condition shall be met. (Office of Geotechnical Engineering, 2008):
- The thickness of the granular material must be sufficient to develop acceptable pressure distribution over the wet
- The backfill material must be able to withstand the wheel load without
- The compaction of the backfill material should be in accordance withtheย standardย ย Basedย onย experience,ย 300ย toย 600ย mm granular material should be adequate for sub-grade modification or stabilization.
Chemicalย Modificationย /ย Stabilization
Forย close toย halfย aย decade,ย theย concernย ofย theย geotechnicalย engineerย hasย beenย to make poor engineering soil much better. This stimulated research into the available chemical or mechanical means of modifying the soil. These chemicals are mainly industrialย wasteย whichย poseย environmentalย problems.ย Inย theย absenceย ofย organicย matter, when a soil contain a certain amount of fines that cause plastic behaviour of the soil, modificationย isย oftenย recommendedย (Osinubiย andย Katte,ย 1997).ย Modificationย isย aย broad term used to describe any technology or operation that is used to improve soil characteristicsย andย asย withย stabilization,ย itย involvesย theย useย ofย differentย kindsย ofย agents. These agents include cement, lime, bitumen, fly ash, etc. These chemicals have been used either single or in combination with oneย another.
Soil modification or stabilization started since the 1960s in Europe and has spread world-wide, since problematic soils are wide-spread. According to Osinubi (1995) cement and lime, mostly used for modification or stabilization, change the water film on the soil particles, modify the clay minerals to some extent and decrease the soil plasticity index. The main purpose of soil modification is to improve the particles size, plasticity index and durability under adverse moisture and stress conditions (Osinubi, 2002). Traces of the modifying agent(s) are added to the soil mass in appropriate proportions. The modifier and soil must be mixed thoroughly in order to achieve the desired strength and durability. To achieve this goal in the laboratory, the natural soil structure is destroyed by grinding when preparing the soil. In the field however, successfulย modificationย dependsย onย theย abilityย ofย theย modifiersย toย penetrateย largeย lumps of soil which may contain coarse aggregates and to modify the active constituents (Osinubi, 2002). The most appropriate method used for any situation depends on the economics, engineering requirement and the soil characteristics which have to be determined.
CHAPTER THREE
MATERIALS AND METHODS
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ย Materials
ย Black Cotton Soil
The soil sample used for this study was collected at the Chad Basin Development Authority (CBDA) reserved site at New Marte (Latitude 13o27IN and longitude 13o50IE) along Maiduguri โ Gamboru Road in Borno State. It was collected as disturbed sample at a depth between 0.5 m to 1.5 m after removing the top soil to avoidย organicย matter.ย Theย soilย sampleย wereย taken,ย sealedย inย plasticย bagsย andย putย inย sack for determination of natural moisture contents. The soil samples were then allowed to dryย beforeย pulverizingย toย obtainย particleย passingย sieveย BSย No.ย 4.ย Aย studyย ofย geological and soil maps of Nigeria after Akintola (1982) and Areola (1982), respectively,ย shows that the parent materials in the study area is basic igneous rock which whenย weathered formedย weaklyย developedย blackย cottonย soil.ย Thisย locationย liesย withinย northย easternย part of Nigeria extensively covered by black cottonย soil.
Locust Bean Wasteย Ash
The locust bean waste ash (LBWA) used for the study was obtained locally from the burning of the locust bean husks source from Doko, Vunchi and Agaie villages around Bida area in Niger State. The husk of locust bean generated through human activities were collected from dumps in the villages and stockpiled. Smith (1992) as well as Mohammedbhai and Baguant (1990) reported that heat treatment plays a vital role in the production of pozzolanas from agriculture waste. Therefore stockpiled husk of locust bean generated was burnt to ash in open air on a galvanized ironย roofingย sheetย andย cooledย beforeย beingย passedย throughย BSย Noย 200ย sieveย andย keptย to be mixed with the soil cement in the appropriateย percentages.
The oxide composition of the locust bean ash was determined at the Centre for Energy Research and Training (CERT) A.B.U, Zaria by the method of Energy Dispersive X โ Ray Fluorescence (XRF). The specification for pozzolanas are given in
CHAPTER FOUR
RESULTS AND DISCUSSION
Properties of Material Used in the Study
ย Naturalย Soil
The result of the test for the identification of the natural soil and the properties revealed that the soil has very high moisture content of 35%, this is attributed to the period of sample collection (during rainy season). The index properties and oxide compositionย ofย theย blackย cottonย soilย areย summarizedย inย Tablesย 4.1ย andย 4.2,ย respectively. Based on the American Association of State Highway Transportation Officials (AASHTO,ย 1986)ย classification,ย theย soilย isย classifiedย asย anย A-7-6ย (24)ย andย basedย onย the Unified Soil Classification System (USCS) the soil is a CL soil. The soil is greyish black in colour (from wet to dry) with a liquid limit of 63%, plastic limit of 27% and plasticity index of 36%. Details of test result are shown in Tables A4.1 to A4.4 in the appendix.
Basedย onย theย Nigerianย Generalย Specificationย (1997)ย andย theย Highwayย Research Board (1943), suitability limit of 50% passing BS No. 200 sieve, 40% liquid limit and 18% Plasticity Index requirements the soil is found to be unsuitable for direct use as a base course or sub-base course and would therefore require initial modification to improve itsย workability.
CHAPTER FIVE
CONCLUSION AND RECOMMENDATIONS
Conclusion
Theย preliminaryย investigationย conductedย onย theย naturalย blackย cottonย soilย collected atย theย Chadย basinย Developmentย Authorityย (CBDA)ย Newย Marte,ย Bornoย Stateย showsย that the soil falls under A-7- 6 (24) classification for AASHTO(1986) and CL using the Unifiedย Soilย Classificationย Systemย (USCS).ย Theย naturalย soilย hasย highย moistureย content of 35% because it was collected during the rainy season. It has a liquid limit value of 63%, plastic limit of 27% and plasticity index of 36% specific, gravity of 2.01 and the predominant clay mineral is montmorillonite. All these properties indicate that theย soil isย highlyย plasticย withย aboutย 80%ย ofย theย soilย particlesย passingย theย BS.No.ย 200ย sieve.ย The workability of the soil is very low and this makes it unsuitable for geotechnical engineeringย use.
In an effort to improve the workability of the soil for engineering purpose, the air dried sample were treated with up to 4% OPC to 8% LBWA blend in stepped concentration of 0,2,4,6 and 8% by dry weight of the soil. The test conducted showed thatย theย percentageย ofย particlesย passingย theย BSย No.ย 200ย seiveย sizeย tremendouslyย reduced from 80% for the natural soil to almost zero for all the energy levels considered. Also the liquid limit of the natural soil increased from 63 to 79% at 4%OPC / 6% LBWA treatment.ย Theย plasticย limitย howeverย decreasedย fromย 26.6%ย forย theย naturalย soilย toย 24.6% at 4%OPC/6% LBWA treatment. The plasticity index for all the concentration of additive exceeded 12% value prescribed for sub-base and base courses by Nigeria General Specificationsย (1997).
The MDD increased for soil compacted using British Standard light energy level from 1.30Mg/m3ย forย theย naturalย soilย toย 1.48ย Mg/m3 atย 4%ย OPCย /ย 6%LBWA treatment. For WAS compaction the MDD increased from 1.42 Mg/m3 for naturalย soil to 1.55 Mg/m3ย at 4% OPC / 6% LBWA treatment. For BSH compaction, the value increased from 1.50 Mg/m3ย for the natural soil to 1.62 Mg/m3ย at 4%OPC/6% LBWA treatment. The OMC on the other hand decreased with higher compactive efforts, but increased with high LBWA content. The optimum moisture content values at the naturalย statesย increasedย fromย 24,ย 21ย andย 19%ย toย 39,33ย andย 30%ย whenย compactedย using BSL,ย WASย andย BSHย energiesย atย 4%OPC/6%LBWAย treatment,ย respectively.
The angle of internal friction for the cement modified soil increase while the cohesion decreased. The angle of internal friction values increased from 180,140ย and 160ย forย theย naturalย soilย toย 35.5o,45oย andย 40oย atย 4%OPC/6%ย LBWAย blendย forย BSL,ย WAS and BSH compaction, respectively. The cohesion value decreased from 75,ย 70 and 60kN/m2ย for natural soil to 22, 15 and 20 kN/m2ย treatment for BSL, WAS and BSH compactions,ย respectively.
Recommendation
Based on the results of the investigation of the effect of locust bean waste ash on cement black cotton soil, an optimum of 4% OPC/6% LBWA is recommended for the modification of black cotton soil used in road construction.
REFERENCES
- AASHTO (1986). Standard Specifications for Transportation Materials and Methods ofย Samplingย andย Testing.ย 14thย Edition,ย Americanย Associationย ofย Stateย Highway and Transport Officials (AASHTO), Washington,ย D.C
- Abdullahi M. (2003) The Use of Rice Husk Ash in Low โ cost Sandcrete Production.
- Unpublished M. Eng. Thesis, Department of Civil Engineering, Federal University of Technology, Minna
- Akinmade (2008). The Effects of Locust Bean Waste Ash on the Geotechnical Propertiesย ofย Blackย Cottonย Soil.ย Unpublishedย M.Sc.ย Thesis,ย Departmentย ofย Civil Engineering, Ahmadu Bello University,ย Zaria.
- Akintola, F. A. (1982). โGeology and Geomorphology.โ In : Nigeria in Maps edited by M. Barbous, Hodder and Stoughton, London.
- Areola, O. (1982). โSoilโ In: Barbous, K.M. (eds) Nigeria in Maps Hodder and Stoughton, London.
- ASTM C618 โ 78(1978). Specification for Fly Ash and Raw or Calcined Natural Pozzolanas for Use as a Mineral Admixture in Portland Cement Concrete. American Society for Testing and Materials, Philadelphia.
- ASTM (1992). Annual Book of Standards Vol. 04.08, American Society for Testing and Materials, Philadelphia.
- BS, 1377 (1990). Methods of Testing Soil for Civil Engineering Purposes. British Standards Institute, London.