CHAPTER ONE

1.0INTRODUCTIONThe word laterite describes no material with reasonable constant properties. To those in the temperate countries it could be described as red friable surface. To those in the hilly tropical countries, it could be described as a very hard homogenous vascular massive clay infill of soft aluminium oxide of yellowish colour and in less hilly country, it could exist as a very hard, soft coarse angular red. (Amu, et.al. a, 2010)A lot of Laterite gravels, which are good for gravely roads, occur in tropical countries of the world, including Nigeria (Osinubi, 1994). There are instances where a laterite may contain substantial amount of clay minerals that its strength and stability cannot be guaranteed under load, especially in the presence of moisture. These types of laterite are also common in many tropical regions including Nigeria where in most cases sourcing for alternative soil may prove economically unwise but rather to improve the available soil to meet the desired objective (Osinubi, 1994). The needs for good road network are extremely increasing with increase in population and also maintenance of the existing one. The physical properties of the soil can be improved (Amu, et.al. a, 2010). Soil improvement could either be by modification or stabilization or both. Over the times, cement and lime are the two main materials used for stabilizing soils. Thus the use of sugar industries solid waste, such as Sugarcane Bagasse Ash (SCBA) will considerably reduce the cost of construction and as well reducing the environmental hazards they cause if found to be useful. Lime, by the nature of its chemistry, produces large quantities of Co2 for every tonne of its final product. Therefore, replacing proportions of the lime in soil stabilization with secondary cementations material like SCBA will reduce the overall environmental impact of the stabilization process (en.wikipedia.org). Bagasse ash has been categorized under pozzolanas with about 60-70% silica and about 9% and 3% Alumina and iron oxides, respectively (Ogbonyomi, 1998). The silica is substantially contained in amorphous form, which can react with the lime librated during the hardening process to further form cementation compounds. This will go a long way in actualizing the dreams of the Federal Ministry of works in Nigeria of scouting for readily cheap construction materials.

1.1 STATEMENT OF THE RESEARCH PROBLEMThere are instances where a laterite may contain substantial amount of clay minerals that its strength and stability cannot be guaranteed under load, especially in the presences of moisture. These types of laterite is also common in many tropical regions including Nigeria where in most cases sourcing for alternative soil may prove economically unwise but rather to improve the available soil to meet the desired objective.Over the times, cement and lime are the two main materials used for stabilizing soils. These materials have rapidly increased in price due to the sharp increase in the cost of energy since 1970s.The over dependence on the utilization of industrially manufactured soil improving additives (cement, lime etc), have kept the cost of construction of stabilized road financially high. This so far, has continued to prevent the underdeveloped and poor nations of the world from providing accessible roads to their rural areas that constitute the higher percentage of their population. These and many other reasons have made it necessary for the construction industry to search for local additives as substitutes for lime and cement.

1.2 JUSTIFICATION OF THE RESEARCHThe ever increasing cost of civil engineering construction coupled with our present economic situation makes it more difficult for government to embark upon new infrastructural developments. This necessitates the initiation of researches into the possibility of using locally available materials as against the conventional materials are either imported or the machinery to produce them are imported thus making their cost to be very high. The use of cement, lime and fly ash has enhanced the engineering properties of lateritic soils (Gidigasu, 1976), however the cost of these materials is on the increase and if construction works are to be carried out economically, some urgent solutions must be proffered in order to reduce the cost burden of stabilization. Sugarcane Bagasse ash is cheaply available locally and is obtained through the burning of Sugarcane which is an agricultural by-product. Therefore if positive result is achieved, the use of Sugarcane Bagasse ash as an additive for soil stabilization will go a long way in reducing the cost of soil stabilization.

1.3 AIM OF THE RESEARCHThe research project is aimed at determining the effect of Sugarcane Bagasse Ash (SCBA) on lime stabilized laterite.1.4 OBJECTIVES OF THE STUDYThe main objectives of this research project include the following:1. To investigate the effect of Sugarcane Bagasse Ash (SCBA) on soil with respect to compaction characteristics, California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS) tests.2. To determine the potentials of using Sugarcane Bagasse Ash (SCBA) mixture with less lime contents for laterite soil stabilization.3. To compare experimental results to established standards. 4. To recommend the use of Sugarcane Bagasse Ash (SCBA) to replace other modifiers such as cement, lime etc in soil stabilization.

CHAPTER TWOLITERATURE REVIEW

2.1 LateritesThere were a lot of controversies on the nomenclature and definition of laterite because of its diversity in engineering and geotechnical properties. One of the numerous definitions that gained wide acceptance in the 19th century when the soil was first discovered was that which define laterite in terms of silica-sesquioxide ratio (Gidigasu, 1976). This definition later lost recognition because of its lack of relationship with the engineering properties of laterite. De-Graft Johnson (1975) defined laterite as a highly weathered material, rich in secondary oxide of iron, aluminium or both which is nearly void of bases and primary silicates but may contain large amount of quartz and kaolinite. This definition is more in agreement with that of Osinubi (2003) who defines laterite as soil groups commonly found in tropical and subtropical regions of the world and formed under weathering condition that favouur laterization (decomposition of ferroalumino silicate minerals leaching of silica and base, and permanent decomposition of sesquioxides within a profile).This later definition has revealed the possible regions of the world where laterite deposits could be found. However, Hunt (1984) had earlier identified specific regions in the middle latitudes which include much of Brazil, the southern third of Africa, south eastern Asia, and part of India as specified regions where laterite deposits could be found. The researcher also identified as not always troublesome since they consist mainly of kaolinite clays, which are relatively inactive and non swelling. But Fletcher and Vernon (1974) described the deceptive nature of laterite that it may appear firm and steep cut could be made into them. But when used as a construction material, it may become soft and unstable. Osinubi (2003) had highlighted factors such as basic or intermediate parent rock material, thick vegetation and high humid residue, permeable profile, heavy rainfall, hot climate and coolish nights, fluctuating water table, etc to have been encouraging and affecting the result of laterization. Where all or most of the aforementioned factors occur simultaneously, massive laterite concretions are formed which could possess enough strength and stability to be used as base material for pavement construction (Osinubi and Bajeh, 1994), (Hunt, 1994). However, some laterite deposits contain high proportions of clay minerals (mostly kaolinite) that it is rarely stable for pavement construction as reported by (Fletcher and Vernon 1974). This is because of the colloidal condition conferred upon the kaolinite mineral particles. According to Bridges (1979), properties, which are conferred upon a soil by the colloidal state, are plasticity, cohesion, shrinkage, swelling, flocculation and dispersion. However, zonn (1986) identified three areas where the clay mineral content of soil must have originated. These include those:i. Inherited from parent rockii. Derived from primary minerals, that is, from partial dissolution and removal of bases from the primary mineral and their substitution by others, eventually leading to a finally dispersed mass.iii. Newly formed, as a result of complete disintegration of the primary minerals and the synthesis of their products.This latter phenomenon is most often observed in the warm humid conditions of the tropics during laterization. Red colour is so much associated with laterites that it is included in almost all its definitions. Zonn (1986) however stated that red colour of whatever shade indicated that the soil is rich in iron or free iron (Fe2O3). Yellow is also connected with iron but indicates the dominance of its hydrated compounds namely Fe (OH)3. Green or dove gray indicates a high concentration of ferrous compounds (FeO). Black and Grey are related to different soil content of humus, and occasionally are due to the colour of parent rock or the presence of volcanic ash. A white colour indicates the present of quartz, kaolinite or calcium carbonate.Laterite deposits usually cap the top of high pediments and vary in thickness from 1m to 6m. It is known to be widely distributed in Nigeria (Durotoye 1983). According to De-Graft-Johnson (1975), laterite materials though variable in texture consist of all soil size of fractions: boulders, cobbles, gravels, sands, silts, and clays. This textural nature of laterite favours the engineering and geotechnical properties of most laterites and made most of it potential construction materials in whichever region the deposits are found. It also allows for easy handling of the material for construction. Few laterite deposits that are not favored by their texture, say by the way of possessing excessive fines, could easily be improved for engineering purposes. 2.2 Properties of Laterites:The common chemical compositions of laterites according to Gidigasu (1976), Ola (1983), Osinubi (2003) are silica (SiO2), sesquioxide of iron (Fe2O3) and aluminum (Al2O3), and in some few cases, little quantities of manganese (Mn), titanium (Ti), chromium (Cr), and vanadium (V). Though silica is low in most laterites soil deposits, higher amounts are found in some few laterite deposits where the parent rock contains a lot of quartz. Gidigasu (1976) has reported higher sesquioxide of between 20-50% for West Africa laterite soil deposits as against black clays, which possess less than 20%. The presence of sesquioxide especially that of iron (Fe2O3) imparts on the laterites the property of hardening on firring. This phenomenon was confirmed by Adeyemi et al (1990) who conducted a study on laterite collected from three different areas in the southern part of Nigeria to evaluate the strength of both the air dried and fired bricks made of these laterite clay deposits. It was observed that firing increased the compressive strength of laterite collected from the first area by three times compared to that of the air dried one. Those of the remaining two areas increased in strength by eight times compared to the air- dried one. Higher iron oxide (Fe2O3) content of the laterite soil deposit of the last two areas was reported to have been the cause of the difference in the compressive strength.Nigerian laterites fall between classes A-1-a and A-7-6 of the American Association of state Highways and Transportation Officers (AASHTO) classification system (Ola, 1983). The researcher also conducted a study on the fine fraction of the laterite soil deposits passing the British standard (BS) sieve No.200 using X-ray diffraction analysis and found that most laterite soil deposit in Nigeria are composed predominantly of kaolinite minerals with some quartz. The kaolinites were confirmed by the presence of 7.16A peaks, which disappeared after heat treatment. The presence of quartz was also confirmed by the 4.26A reflection and by narrow characteristics peak at 3.36A. Swelling material like vermiculite and montmorillonite were absent. Similar result was also observed by Osinubi and Katte (1997) from the result of the study conducted on a laterite soil deposit along Zaria-Sokoto road. X-ray diffraction analysis and differential thermal analysis of soil fraction passing B.S sieve No.200 confirmed the predominance of kaolinite clay minerals with quartz.Bases such as calcium oxide (CaO), sodium oxide (Na2O), magnesium oxide (MgO) e.t.c. have been observed to be always absent in laterite soil deposits (Gidigasu, 1976). The activity of some laterite soil deposits has also been studied and reported (Osinubi, 2003). The pH of most West African laterite deposits have been reported to be gradually below 2% in the top soil. The activity and low organic matter content of laterite deposits favor the modification and stabilization of laterite soils considering influence of pH on stabilization using resinous material and the inhibitive influence of organic matter on hydration of cements (AFJMAN, 1994).The range of index values of some laterite soil deposits in Nigeria was reported by Madu (1975). Liquid limits and plastic limits were found to range between 45.0%-57.2% and 22.0%-40.4% respectively. The plasticity index and shrinkage limits also lie within 16.0%-24.0% and 8.6%-14.8% respectively. However Gidigasu (1976) reported higher values of liquid limits and plasticity index of above 50% and 30% respectively for ferralitic lateritic soil deposits in contrast to those of the ferruginous laterite soil deposits, which are below 50% and 30% respectively. The engineering properties of laterite soil deposits vary widely in the same manner as its texture. Gidigasu (1976), and Ola (1983), reported California bearing ratio (CBR) values of as low as 2% for problem laterite to as high as more than 200% for good laterite soil deposits. Maximum dry densities as low as 1.50Mg/m3 to as high as 2.4Mg/m3 has equally been recorded at British standard light (BSL) compaction energy. It is expected that higher compaction energy will give higher results. Low unconfined compressive strength (UCS) of 200KN/m2 has been reported (Osinubi, 2003).2.3 pozzalanas:American society of testing and materials (ASTM C618-93) defines pozzolan as a siliceous or siliceous and aluminous material which in itself possess little or no cementation value but will, in finely divided form and in the presence of moisture, chemically react with lime (librated by hydrating Portland cement) at ordinary temperatures to form compounds possessing cementation properties. According to Neville (2000), the original reason for using these materials are usually economics: they are by products or wastes from industrial processes. However, it is important that pozzalanas be in a finely divided state as it is only then that silica can combine with calcium hydroxide Ca (OH)2 in the presence of water to form stable calcium silicate which have concentration properties.Over 2000 years ago, Egyptians, Romans, and Greeks used gypsum and lime only while the Kuwaitis and Indians used ordinary earth, mud bricks, burnt clay together with lime for building. But with the advent of ordinary Portland cement (OPC) in 1824 attention generally shifted to the use of OPC as an effective cementing material for construction purpose. However, these older pozzalanas-volcanic ash, turfs, pumicides, opaline shales and cherts, fly ash, basalt stone are still in use in Kenya, India, and Guyana (Smith, 1992).Recent discoveries show the possibilities of the use of agricultural wastes for producing cementitious compounds with lime. Many plants during their growth pick up silica from ground into the structure of their leaves, stalks and other parts. When residues of these plant are burnt, organic material, which is the largest proportion, is broken down and disappears as carbondioxide and water vapour etc. The ash remaining contains mostly in organic residues notably silica (Smith, 1992). Pozzalanas can be divided into two groups: natural and artificial pozzalanas,2.3.1 Natural Pozzalanas These are mostly materials of volcanic origin but could include certain diatomaceous earth. These include (Ogbonyomi, 1998)a. Volcanic tuff: These materials originate from the deposition of volcanic dust and ash. These materials have been thrown out by volcanoes in recent times or long ago, which contain finely divided materials, high in silica or aluminum content.b. Diatomaceous earth: These are composed of the siliceous skeletons of diatoms deposited from either fresh or seawater. In some cases, the deposits are mixed with sand or clay.2.3.2 Artificial Pozzalanas:The main artificial pozzalanas are burnt clays and shales, pulverized fuel ash (Neville, 2000), some other recent discoveries are calcined basalt stone, rice-husk ash (RHA), and bagasse ash. The last two are obtained from agricultural wastes.a. Burnt clay and shales: These type of pozzalanas are produced by burning suitable clays or shales at a temperature of between 600C to 900C depending upon the nature of the clay and the condition of burning. These materials turn pozzalanic because of the constituents of the clay, which are mainly hydrated alumino silicates with three different groups of kaolinites, illites and montmorillonites.b. Pulverized fuel ash: This is a by-product of burning of coal in boilers and approximates to burnt clay, which is high in alumina and iron oxide in composition, The particles are roughly spherical in shape, and in finely divided form has specific surface of 2000cm2/g to 5000cm2/g (Neville, 2000).c. Calcined basalt stone: it has been reported by Smith (1992) that basalt treated to a temperature range of 500C to 800C exhibits pozzalanic activity, The optimum temperature will differ from one stone source to anotherd. Rice-husk ash (RHA): About 20% of the weight of rice paddy processed in rice mills is discarded as husk (Ogbonyomi, 1998). The (RHA) remaining after the burning of the husk constitutes about 20% weight of the husk. Various researchers and authors (Road note 31, 1990), Ogbonyomi (1998), Smith (1992), Abdullahi (2003), have categorized rice-husk ash as pozzalana with high amount of amorphous silica and alumina. It is advisable to burn the husk in a purpose made incinerator with maximum temperature of 750C to avoid the risk of producing less reactive ash (Smith, 1992).e. Bagasse ash: This is a fibrous residue after the extraction of sugar juice from sugarcane, and poses a disposal problem in sugar factories especially in developing countries like Nigeria. According to Misari et al (1998), the estimated land under sugarcane cultivation in Nigeria is between 25,000 to 30,000 ha. However there is a potential for land under sugarcane cultivation to be expanded to 147,000ha. Also, sugarcane yield in Nigeria was estimated at 80 tonnes per hectre, which leaves the amount of sugarcane produced in Nigeria today at between 2 million tones and 2.4 million tonnes. According to Ogbonyomi (1998) the estimated average amount of bagasse from sugarcane is 30% and the ash content from bagasse is 2.48%, which leaves the amount of bagasse , produced in Nigeria annually to lie between 600,000 tonnes and 720,000 tonnes while the amount of bagasse ash produce lies between 14,880 tonnes and 17,856 tonnes. Some of this bagasse is burnt to generate steam at the factories for the production processes, but this still leaves the problem of disposing the bagasse ash. As mentioned earlier, this ash has been found to contain a substantial amount of silica and alumina and has been categorized under pozzalanas (Ogbonyomi, 1998). These oxides in their reactive form can take part in cement-like setting reactions with lime or ordinary Portland cement. In Mauritius, research has shown that a 20-30% replacement of ordinary Portland cement (OPC) with bagasse ash yielded a useful cement strength value, which at upwards of 4 months compared favourably with OPC mixes (Smith, 1992). Other use of bagasse as reported by Ogbonyomi (1998) include for paper production, ceiling, wallboard, alpha cellulose, plastics and cattle bedding.2.4 Admixture Stabilization: There are instances where the lacking properties of a particular soil cannot be restored by a single chemical additive like cement, lime, bitumen, e.t.c. or a required strength cannot be gained by an economic amount of a single additive. In these types of circumstances, two or more chemical additives could be required to restore the lacking properties or required strength with an economic amount of an additive. For instance, cement, which is the cheapest and most available soil stabilization additive in Nigeria, cannot be used economically on very soft clays. But addition of lime to this type of clay can help to increase its workability and hence high reduction in the amount of cement that would have been required for efficient stabilization of that clay.Prolong increase in strength with economic amount of cement can also be achieved with addition of any pozzalanic material along with the cement. This is due to the reaction between the pozzalanas and the lime liberated during hydration reaction of cement. This prolong reaction has urged some researchers to employ a new evaluation criterion for soil stabilization using a combination of an additive and a pozzalana since the only available criteria available have that of cement and lime. One of the recent laboratory trials to achieve this objective is that of Osinubi (1990). Who evolved an evaluation criterion for cement stabilized residual black cotton soil when lime is used as an admixture. It was concluded that, due to time dependent increase in strength and attendant high durability due to enhanced pozzalanic reaction of the soil-lime-cement mixture, an unconfined compressive strength (UCS) of 1235kN/m2 and a California bearing ratio of 55% are recommended as evaluation criteria as against the (UCS) of 1720kN/m2 and (CBR) of 80% recommended by BS 1924 (1990) and Nigerian General Specification for Road and Bridges Works (1997).Toro (1997), Osinubi (1999), and Osinubi and Medubi (1997), conducted laboratory studies on admixture stabilization of various chemical additives and have recorded substantial increase in strength (CBR) and (UCS) after some reasonable days of curing, usually 7, 14 and 28 days of curing. However, the variation of maximum dry density and optimum moisture content of these mixtures with increase in admixture contents is not consistent like those of single additives. Rather it could increase and decrease at no constant additive contents due to complex reactions between the additives and the soil to be stabilized.

2.5 StabillizationVarious researchers: Gillott (1968), Gidigasu (1976), Singh (1991), AFJMAN (1994), Toro (1997), Adeyemi and Abolurin (1999), defined stabilization in their own words but with the same meaning. The more involving is that given by Singh (1991) who defined stabilization as the combination of soils and or other additives in such a way that, when it is compacted under specified conditions and to specified extent, would undergo material change in its properties and would remain in its stable compacted state without undergoing any change under the effect of exposure to weather and traffic. The main properties in engineering practice, which may require improvement, are strength, permeability, volume stability, and durability (Toro 1997), There are wide ranges of engineering services where stabilization can be applied. These include,a. Foundations: To reduce settlement or heave under buildings either by ensuring volume stability, or controlling permeability or increasing strength (Toro, 1997).b. Excavation works: To provide support in pits, trenches, tunnels, e.t.c. by strengthening the surrounding soil or varying its permeability. The methods used are mainly accelerated drainage and grouting.c. Pavement construction: It provides pavements of higher strength and durability for highways, airfields, and railways. The methods used are basically mechanical or chemical stabilization.d. Slope stability: This is to prevent slips on cut slopes, embankments, and natural slopes. Methods mainly applied are drainage, surface seals e.t.c. similar method of application was reported by Anderson and Richard (1989) to have been a tradition in Hong Kong long before now. A soil-cement plaster known locally as chunan was often used as a slope protection against infiltration and erosion. The mix consists of one part cement, three parts hydrated lime, and twenty parts soil and water mix together to the required consistency and applied to the surfaces of the slope.e. Water retention: To protect structures against water erosion especially for dams, tanks, canals e.t.c. Methods in common use are lime treatment to control erosion or reduce permeability of the soil.f. Environmental conservation: To prevent erosion, combat dusting of road surfaces e.t.c. by increasing the resistance of soil to natural weathering from wind or water. A new field of environmental geotechnics has evolved the use of stabilized clay liners to prevent the combination of ground water from waste deposited on ground surface. The stabilization is mainly by cement, lime e.t.c. (Kerry et al 1995).g. Thickness reduction: To reduce the thickness of a pavement below what it would have been without stabilization (AFJMAN, 1994). Since pavements are commonly designed using CBR curves, stabilizing the soil to higher strength and stability can reduce the thickness of pavement.During the last four to five decades, numerous stabilizing processes or method have been used. These include mechanical stabilization and chemical additives such as Portland cement, hydrated lime, gypsum, alkalis, sodium chloride, calcium chloride, silicate resins, ammonium compounds, agricultural and industrial waste products (Webb, 1992). However, because of cheapness or availability in most developing countries, the most widely used additives are Portland cements, lime, bitumen and agricultural waste to a less extent.2.5.1 Bituminous stabilization:Bitumen has been categorized under water proofing agents by Yoder and Witezak (1975) and is one of the main properties it imparts on soils when used for stabilization. Generally, there are two mechanisms by which bitumen stabilizes soils (Ola, 1975), (Gidigasu, 1976), (AFJMAN, 1994), (Osinubi, 2001a). The first process is the cementation or adhesive process, which increases the strength of coarse grained soils but may decrease the strength of fine-grained soils. The basic mechanism in asphalt stabilization of fine-grained soils is a water-proofing phenomenon. Soil particles or agglomerates are coated with bitumen that prevents or slow the penetration of water, which could have resulted in decrease in soil strength. In non-cohesive materials, such as sands and gravels, both the mechanism of water proofing and adhesion occurs. The strength increase due to adhesion continue to the optimum bitumen content after which the strength will drop due to decrease in grain to grain contact and hence reduced mobilization of shear strength. Ola (1975), Osinubi and Bajeh (1994), Osinubi (2001b), have conducted laboratory trials on the potentials on various types of bitumen in laterite soil stabilization. They all reported increase in strength of a A-7-6 (AASHTO Classification system) laterite soils to an optimum bitumen content of 4% (Ola, 1975), 5% (Osinubi and Bajeh, 1994), and 6% (Osinubi, 2001a,b) after which the strength dropped in all cases. The studies also showed decrease in maximum dry densities and optimum moisture content with increase in bitumen contents and do not rise at higher bitumen contents.2.5.2 Mechanical stabilization:This refers to either compaction or the introduction of fibrous and other non-biodegradable reinforcement to the soil (Huffman, 1995). It involve the altering of soil properties by changing the gradation through mixing with other soils, densifying the soils using compaction efforts, or undercutting the existing soils and replacing them with granular materials.A common remedial procedure for wet and soft layer is to cover it with granular material or to partially remove and replace the wet subgrade with a granular material to a pre-destined depth below the grade lines. The compacted granular layer distributes the wheel loads over a wide area and serves as a working platform.To provide a firm-working platform with granular material, the following conditions shall be met:1. The thickness of the granular material must be sufficient to develop acceptable pressure distribution over the wet soils.2. The backfill material must be able to withstand the wheel load without rutting.3. The compaction of the material should be in accordance with the standard specifications.2.5.3 Cement Stabilization: Depending on the soil type 3% to 10% of cement by weight of dry soil is mixed with the soil to cause it to harden into a compact mass, which will not soften in the presence of water. Cementation is based on hydration of cenment. The major hydration products are a series of calcium silicate Hydrates (CSH) and hydrated lime, Ca (OH) 2. Reactions of soil with cement include replacement of Ca++, adsorption of Ca (OH) 2 by particles and cementation at inter-particle contacts by the CSH gel. When clay-grade materials are present in excess of about 30% it is more difficult to achieve economic stabilization by use of cement due to great difficult in pulverizing and mixing (Gillot, 1968).

2.5.3.1 Cement Stabilization MechanismCement hydrates when water is added, producing cementatious compounds independently of soil. These products are calcium silicates hydrates, calcium aluminates hydrates and hydrated lime. The first two products constitute the major cementatious components, whereas the lime is deposited as separate crystalline solid phase. The increase in strength is due to the development of cementatious linkages between these hydration products and soil particles. The lime released during the hydration of the cement may react with any pozzolanic material, e.g. clay, present in the soil to form a secondary cementatious material which also contributes to inter-particles bonding. Thus a sizeable fraction of the cementatious material formed in soil-cement is contributed by the soil itself (moh, 1967)2.5.4 Lime Stabilization:Lime stabilization is achieved with calcium oxide (quick lime) or calcium hydroxide (slaked lime). The stabilization mechanism of lime is similar to that of cement. Lime acquires silica or other pozzolanas in the soil to form CSH gel. Lime stabilization improves the strength, stiffness and durability of fine grained materials. In addition lime is sometimes used to improve the properties of the grained fraction of granular soils. Lime has been used as a stabilizer for soils in the base courses or pavement systems, under concrete foundations, on embankment slopes and canals linings. (Murthy, 2009).Adding lime to soil produce a maximum density under higher optimum moisture content than in the untreated soil. Moreover, lime produces a decrease in plasticity index.\Lime stabilization has been extremely used to decrease swelling potential and swelling pressures in clays. Ordinarily the strength of wet clay is improve when a proper amount of lime is added. The improvement is partly due to decrease in plastic properties of the clay and partly to the pozzolanic reaction of lime with soil, which produces cemented material that increases in strength with time. Lime treated soil in general have greater strength and higher modulus of elasticity than untreated soils. (Murthy, 2009).2.5.4.1Lime Stabilization Mechanism:In white lime stabilization, there is no direct hydration to form cementatious compounds. There is a physical and a chemical component to the reaction of lime with clay. The physical reaction is one of cation absorption, calcium first replacing any other ion present as a Base Exchange ion. This is followed by the flocculation into groups of coarse particles, which produce an immediate increase in strength.For the chemical component of the reaction Moh, (1967) has suggested the secondary reaction in the soil-cement hydration. Thus the addition of lime to a soil causes an immediate increase in the pH of the molding water, due to the partial dissociation of the calcium hydroxide. The calcium ions in turn combine with the reactive silica or alumina or both, which harden on curing to stabilize the soil.2.5.5Bagasse Ash:Bagasse is the fibrous residue obtained from sugar cane after the extraction of sugar juice at sugar cane mills (Osinubi and Stephen, 2007). This material usually poses a disposal problem in sugar factories particularly in tropical countries. Research works have been carried out on the improvement of geotechnical characteristics of soils using bagasse ash (Osinubi and Stephen, 2007). Nowadays, it is common place to reutilize sugar cane bagasse as a biomass fuel in boilers for vapour and power generation in sugar factories. Bagasse is rich in amorphous silica which indicates that it has pozzolanic properties, depending on the incinerating condition of the bagasse; the resulting sugar cane bagasse ash may contain high level of Silicate oxide (SiO2) and Aluminium oxide (Al2O3) enabling in its use as supplementary cementatious material.Bagasse ash can improve the compressive strength of cement-based materials. As stated by Cordeiro et al. (2008), the improved compressive strength depends on both physical and chemical effects of the sugar cane bagasse ash. The physical effect (the filler effect) is concerned with packing characteristics of the mixture, which in turn depends on the size, shape and texture of sugar cane bagasse ash particle. The chemical effects relates to the ability of the bagasse ash to provide reactive siliceous and/or aluminous compounds to participate in the pozzolanic reaction with calcium hydroxide and water. The product of such reaction is called calcium silicate hydrate, a compound known to be responsible for compressive strength in cement-based materials.The pozzolanic reactivity of sugar cane bagasse ash depends strongly on the incinerating temperature, a maximum reactivity occurred at 500C (Cordeiro, 2008). The main reasons why pozzolans like bagasse ash have poor pozzolalic activity is due to over burning into temperature range that favors the development of crystalline (less reactive) rather than the amorphous (more reactive) particles. Burning of bagasse at a temperature higher than 500C causes most amorphous SiO2, to transform to its crystalline less reactive form called cristobalite, therefore worsening the pozzolanic activity of sugar cane bagasse ash. Based on the pozzolanic characteristics of bagasse ash, it can serve as an attractive waste material candidate to be used as a supplementary cementatious material (SCM) (Sirirat and Supaporn, 2010).

2.5.5.1 Application of Bagasse Ash:With pozzolanic properties, bagasse can be used as a partial cement replacement in concrete for high performance and strength, low permeability concrete for use in marine environments. Bagasse use are wide and varied due to its wide spread availability and low cost. It is often used as a primary fuel source for sugar mill, when burned in quantity, it produces sufficient fuel source for sugar mills, when burned in quantity, and it produces sufficient heat energy to supply all the needs of a typical sugar mill with energy to spear.Bagasse is also used to make disposable food containers, replacing materials such as Styrofoam, which are increasingly regarded as environmental unacceptable (en.wikipedia.org). It can also be used in variety of applications such as flame retardants, insecticide and bio-fertilizer, insulator and ceramic glaze. It has also been shown to be suitable in geo-environmental application for treatment of lateritic soil in construction of compacted clay liners for landfills (Eberemu, 2008).

CHAPTER THREEMATERIALS AND METHODS3.1Materials3.1.1Lateritic SoilThe soil sample used for this study was collected by method of disturbed sampling from a borrow pit located on the left hand side of Zaria-Funtua road before the new Ahmadu Bello University Teaching Hospital in Shika area of Zaria (Longitude 7 36 E Latitude 11 4 N). The soil samples were collected at a depth between 1.5 and 2.0 m corresponding to the B horizon usually characterized by accumulation of material leached from the overlying A horizon. A study of the geological map of Nigeria after Akintola (1982) and the soil map of Nigeria after Areola (1982) reveals that the soil belongs to the group of ferruginous tropical soils derived from acid igneous and metamorphic rocks.3.2Chemical Additives3.2.1Lime:The lime used for this study is hydrated lime obtained from a retail outlet in a public market.3.2.2Bagasse Ash:The bagasse ash in this research was collected from a sugarcane market at kofar kansakali area of Gwale local government Kano state. The bagasse ash was prepared locally by burning the dry sugarcane residue in an open place and was left for about 24hours under normal environmental condition for the bagasse to ash. The ash was collected in a sack and transported to the laboratory. It was then sieved through a local sieve to get rid of large solid particle present in the ash before passing through the British standard sieve No.200 (75m aperture) and then stored in an air tight container to avoid pre-hydration. The table below shows the oxide composition for bagasse ash. Table 3.1: Oxide composition of bagasse ash (source Mustapha, 2005).OxideComposition

SiO257.95

Al2O38.23

FeO33.96

CaO4.52

MgO4.47

K2O2.41

LOI5.0

3.2.3MethodIndex tests and strength tests were carried out on natural lateritic soil to ascertain the suitability or otherwise of the natural soil for use in pavement structure according to BS 1377 (1990). The second category of tests were carried out on the soil admixed with lime and bagasse ash at various mix ratios according to BS 1924 (1990) to evaluate the suitability of these admixtures as lateritic soil stabilizers. The percentages of lime used were 2, 4, 6 and 8% each admixed with 2, 4, 6 and 8% bagasse ash by weight of the dry soil. The mixtures were compacted to predetermined maximum dry densities and optimum moisture contents for unconfined compressive strength and California bearing ratio tests.3.2.4Soil Classification Tests.3.2.4.1Determination of Natural Moisture Content:The procedure was in accordance with BS 1377 (1990). Some quantity of soil was kept in an air tight polythene leather as soon as the soil was collected from the borrow pit and was brought to the laboratory. Three containers were cleaned and weighed. About 30g of the soil was crumbled and placed in each container. The container and the content were weighed to the nearest 0.01g and placed in an oven at a temperature of 105C to 110C for a period of 24 hours. After drying, the container was removed from the oven and allowed to cool. The container and the content were again weighed. The natural moisture content is given byW = WhereWc = weight of container (g)Ww = weight of container+ wet soil (g)Wd = weight of container+ wet soil (g)W = moisture content (%).3.2.4.2Particle Size Distribution Test:The test was carried out in accordance with BS 1377 (1990) using the method of wash sieving. 200g of the soil was weighed and placed in a clean, dried container and enough water was poured to cover the soil. The mixture was left overnight to allow water to permeate the clods of fine soil. The soil was then washed through an arrangement of two sieves (2 mm aperture size up and 75m BS aperture size down) until the water passing the 75 m BS sieve became clear. Meanwhile, all the water passing through the 75 m was collected in a container and used for hydrometer test. The soil retained on both the 2 mm BS sieve size and 75 m BS sieve size were dried in an oven and dry sieving carried out on them.

3.2.4.2.1Dry Sieve Analysis:Sieves were arranged according to their aperture sizes from 2mm on top through 1.18mm, 0.6mm, 0.425mm, 0.30mm, 0.212mm, 0.15mm, and 0.075mm to the pan on the bottom. Both the soil retained on 2mm sieve size and 75mm sieve size weighed and poured in to the top sieve after drying and sieved through the arrangement of the sieves for between five to ten minute. Meanwhile, the sieves were weighed empty before the sieving commenced. Each of the sieves was again weighed after sieving and the change in masses recorded as mass retained, percent mass retained, and percent mass passing were all deduced.

3.2.4.2.2Hydrometer Analysis:All the soil that was washed through 75m BS sieve was collected and poured in to a 1000 ml graduated cylinder and the mixture made up to 1000 ml mark. The cork of the cylinder was inserted and the solution shaken thoroughly for about 5 minutes after which it was placed on top of a flat table. A hydrometer was immediately inserted and hydrometer reading recorded after 15sec, 30sec, 1minute, 2minutes, 4minutes, 10minutes, 20minutes, 30minutes, 1hr, 2hr, 4hr, 6hr, 12hr and 24hr. The temperature of the mixture was continuously taken during the process-using thermometer. In this way, the particle size distribution of silt and clay size particles was determined.3.2.4.3Atterberg LimitsThe Atterberg limits tests were conducted in accordance with BS 1377 (1990).

3.2.4.3.1Liquid Limit:200 g of a portion of the soil sieved through BS sieve with 425 m aperture was thoroughly mixed with distilled water to form a uniform paste. A portion of the soil water mixture was then placed in the cup of the casagrande apparatus, leveled off parallel to the base and divided by drawing the grooving tool along the diameter through the centre of the hinge. The cup was then lifted up and dropped by turning the crank until the two parts of the soil come into contact at the bottom of the groove. The number of blows at which that occurs was recorded and a little quantity of the soil was taken and its moisture content was determined. The test was performed for well-spaced out moisture content from the drier to the wetter states. The values of the moisture content (determined) and the corresponding number of blows was then plotted on a semi-logarithmic graph and the liquid was determined as the moisture content corresponding to 25 blows.

3.2.4.3.2Plastic LimitA portion of the soil water mixture used for the liquid limit test was retained for the determination of plastic limit. The ball of the soil was moulded between the fingers and rolled between the palms of the hand until it dried sufficiently (even though the soil was already relatively drier than the ones used for liquid limit). The sample was then divided into approximately four equal parts. Each of the parts was rolled into a thread between the first finger and the thumb. The thread was then rolled between the tip of the fingers of one hand and the glass. This continued until the diameter of the thread is reduced to about 3 mm in five to ten forward and backward movements of the hand. The movement continued until the thread shears both longitudinally and transversely. The crumbled soil was then put in the moisture container and the moisture content determined. The whole process was repeated to obtain three values which were averaged to give the plastic limit.3.2.4.3.3Plasticity Index. Plasticity index is the difference between the liquid limit and the plastic limit. PI = LL-PL(3.2)WherePI = Plasticity index LL = Liquid limitPL = Plastic limit3.2.4.4Linear ShrinkageThe test was conducted in accordance with Test 5 BS 1377 (1990). It involves the mixing of about 150 g of soil passing the BS No. 40 sieve (425 m aperture) with water in order to obtain a homogeneous paste (the water added to the natural soil corresponded to the moisture content at liquid limit). The paste was then placed in the shrinkage mould and vibrated gently in order to expel air pockets from the mixture. The soil was then leveled by spatula and air-dried at 60C until the soil shrank clear of the mould. Subsequent drying was made at 105-110C in an oven in order to complete the shrinkage. On cooling, the length of the sample was measured with a ruler and the linear shrinkage was calculated using the equation below:Linear Shrinkage=

3.2.4.4.1Specific GravityThe determination of specific gravity was carried out according to BS 1377 (1990) test (B) for fine-grained soils. The density bottle and the stopper were weighed to the nearest 0.001g (m1). The air dried soil was transferred into the density bottle, and the bottle, content and the cover were weighed as (m2). Water was then added just enough to cover the soil, the solution is gently stirred to remove any air bubble. The bottle was then completely filled up and covered. The covered bottle was then wiped dry and the whole weighed to the nearest 0.001g (as m3). The bottle was subsequently emptied and filled completely with water, wiped dry and weighed to the nearest 0.001g (m4). The specific gravity is calculated using the equation below:

3.3Compaction Characteristics3.3.1British Standard Light (BSL)Empty mould with base plate was weighed. 3 kg of air dried soil passing BS sieve with aperture size 20 mm was also weighed and placed on a flat tray about 1m X 1m. The soil was pulverized using a wooden hammer to avoid crushing of gravel materials contained in the sample. For natural soils, about 4% of water by weight of the dried soil was added immediately. But for admixed soils, appropriate percentages of lime and or bagasse ash are first added to the pulverized soil and mixed dried thoroughly after which 4% of water by weight of the dry soil was added and mixed thoroughly together until the whole mix formed a uniform paste. The mixture was then compacted in the mould with the extension collar attached, by ramming it into 3 layers, each layer been given 27 blows with (2.5 kg) rammer dropped from a height of 300 mm above the soil surface. The blows been uniformly distributed. After compaction of the third layer, the collar was removed and the soil trimmed off even with the top of the mould. The mould and the soil were then weighed. Two representative samples for moisture content determination were obtained from and bottom of the compacted soil.The compacted soil was crumbled, repulverized, remixed with the remaining soil and 6% of water by weight of the dried soil was added to the mixture and the process repeated. The compaction process was repeated each time raising the water content until there was a drop in weight of mould plus wet soil. The results were presented in terms of dry densities using the expression:d = Whered = dry density of the mix (Mg/m3)b = bulk density of the mix (Mg/m3)W = moisture content of the mix (%)3.4Soil Strength Tests:3.4.1Unconfined Compressive StrengthThe unconfined compressive strength (UCS) tests were performed on the soil samples according to BS 1377; 1990 part 7 using the British Standard light (BSL) energy level. The natural soil sample/the stabilized soil samples were compacted in 1000 cm3 moulds at their respective OMC. The samples were extruded from the moulds and trimmed into a cylindrical specimen of 38.1 mm diameter and 76.2 mm length. The three cylindrical specimens from the mould were cured for 7 days, 14 days and 28 days. At the elapsed day of curing, the specimen were then placed centrally on the lower platen of a compression testing machine and a compressive force was applied to the specimen with a strain control at 0.10% mm. Record was taken simultaneously of the axial deformation and the axial force at regular interval until failure of the sample occurred. The UCS of the sample was determined at the point on the stress-strain curve at which failure occurred. The UCS was calculated from the following equation:). (3.6)3.4.2California Bearing RatioThe California bearing ratio (CBR) test were conducted in accordance with BS 1377 (1990) for the natural and treated soils. The CBR is expressed by the force exerted by the plunger and the depth of its penetration into the specimen; it is aimed at determining the relationship between force and penetration.5.0 kg of the soil sample/treated sample were mixed at their respective optimum moisture contents in 2360 cm3 mould, in three layers each receiving 62 blows from the (2.5 kg) rammer.The base plates were removed (after compaction) and the compacted specimens placed in sealed plastic bags for curing (for 6 days) and after the 6th day the specimens were immersed in water for 24 hours before testing according to Nigerian General Specification (1997). The base plates were later replaced and the specimens transferred to the CBR testing machine and positioned on the lower plate of the machine. The plunger was then made to penetrate the specimen at a rate of 1.3 mm/min until the specimen failed. The mould was then inverted, base plate removed and the procedure repeated for the base of the specimens.From the values of the penetration and force recorded, a curve of force against penetration was obtained. The CBR value was calculated at penetration 2.5 mm or 5.0 mm; the greater of the two values and as their means where the value are within 10% of each other. The CBR was calculated as:CBR = Where standard load= 13.24 kN of 2.5 mm penetration= 19.96 kN of 5.0 mm penetration

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