Optimization of Bagasse Ash Content in Cement-stabilized Lateritic Soil
Chapter One
Aim and Objectives of the Study
This work used bagasse ash (sugar-cane residue ash) as an admixture in cement- stabilized Ndoro Oboro lateritic soil for road construction works. The study is aimed at optimizing bagasse ash content in the cement-stabilized soil.
The objectives of this work were to:
- Characterize bagasse ash and lateritic soil.
- Examine the effects of bagasse ash on the compaction and strength characteristics of the cement-stabilized lateritic
- Develop relationships comprising cost of bagasse ash content, cement content, cement-stabilized lateritic soil compaction and strength
- Calibrate and verify the model using experimental
- Develop a non-linear programming model for predicting the optimum content of bagasse
- Optimize bagasse ash content in the cement stabilized lateritic soil and compare results with unoptimized solution.
CHAPTER TWO
LITERATURE REVIEW
Definition of Laterite
The term laterite has been put into diverse usage and controversially defined, since it was first coined by Buchanan (1807) from the latin word ‘later’ which means a brick because it was easily moulded into brick-shaped blocks for building. It was originally described as a ferruginous vesicular unstratified and porous material with yellow ochre due to high iron content.
Joachin and Kandiah (1941) categorized laterite, lateritic and non-lateritic soil based on their silica-sesquioxide ratios, which is represented by SiO2 / (Fe2O3+Al2O3). Ratio less than 1.33 indicates laterites, those between 1.33 and 2.00 indicate lateritic soils and above 2.00 indicate non-lateritic soils, which have also been tropically weathered. A sesquioxide is an oxide with three atoms of oxygen and two metal atoms.
Another definition for laterite was proposed by Little (1969) as igneous rock tropically, partially or totally weathered with a concentration of iron and aluminium oxides (sesquioxides) at the expense of silica. Gidigasu (1976) grouped the various definitions according to the soil-hardening properties, chemistry and morphology. Madu (1977) while agreeing with the residual nature of the laterites, used the silica sesquioxide ratio to divide eastern-Nigeria laterite into two main sub-genetic groups of sandstone laterite and lateritic shales. And also, it was recorded that low iron oxide content in lateritic shales and comparatively high content in the sandstone laterites which was explained to be due to modes of formation of laterites.
Ola (1978) did not agree with Joachin and Kandiah (1941) owing to its inconvenience from an engineering point of view particularly where there is a lack of adequate laboratory facilities. Therefore local terminology was adopted which defines lateritic soils as all products of tropical weathering with red, reddish brown or dark brown colour, with or without nodules or concretion and generally (but not exclusively) found below hardened ferruginous crusts or hard pan.
According to Alexander and Cady (1962) laterite is a highly weathered material, rich in secondary oxides of iron, aluminium or both. It is nearly void of bases and primary silicates but it may contain large amount of quartz and kaolinite. It is either hard or capable of hardening on exposure to wetting and drying. Osula (1984) modified the definition to read “laterite is a highly weathered tropical soil, rich in secondary oxides of any or a combination of iron, aluminium and manganese”. Manganese has been reported as a predominant element in combination with iron in some varieties of laterite, notably those in India (Rastal, 1941). Melfi (1985) defined lateritic soils as soils belonging to horizon A and B of well-drained profiles kaolinite group and of iron and aluminium hydrated oxides. Smith (1998) defined laterite as a residual soil formed from limestone after the leaching out of solid rock material by rainwater to leave behind the insoluble hydroxides of iron and aluminium.
Makasa (2004) stated that the degree of laterization is estimated by silica-sesquioxide ratio (SiO2 / Fe2O3 + Al2O3). In later studies by Schellmann (2008), it was found that intensive chemical decomposition of rocks is a wide spread phenomenon in tropical regions and affects each kind of rock. Obviously, tropical weathering causes an increase of iron indicated by reddish-brown colour of laterites. The progress in chemical analysis of more samples showed that the tropical weathering increases iron content and frequently aluminium content and decreases silica content in relation to the underlying parent rocks. Therefore, attempt was made to define laterites by the ratio Si: (Al + Fe) but a definite limit was not applicable for laterites on different parent rocks. Rather laterites are described to be soil types rich in iron and alminium, formed in hot and wet tropical areas. Nearly all laterites are rusty-red because of iron oxides. They develop by intensive and long-lasting weathering of the underlying parent rock. The majority of the land areas with laterites was or is between the tropics of cancer and capricon which include stable areas of African Shield, the South American Shield and the Australian Shield. Laterites on mafic (basalt, gabbro) and on ultramafic rocks (serpentine, peridotite, dunite) are formed from these rocks which are free of quartz and show lower silica and higher iron content while laterites on acidic rocks (not only granites and granitic gneisses but also sediments as clays, shales and sandstone shall be included) are formed from rocks which contain quartz and have higher silica and lower iron contents. The main element percentages of rocks from these two groups and their corresponding laterites are shown in Table 2.1 and the percentages shown are typical average values of numerous laterite samples and their parent rocks in many tropical countries.
CHAPTER THREE
MATERIALS AND METHODS
Introduction
The soil sample was collected from a lateritic soil deposit in Oboro, Ikwuano Local Government Area of Abia State. It was collected at a depth of not less than 150mm at 15 different points of about 3m apart using the disturbed sampling technique. The natural moisture content was determined after which it was air-dried. The Ordinary Portland Cement was used as the binder and bagasse ash as the admixture in the stabilized soil while clean tap water was used for the mixing. The bagasse residue was collected from Panyam district, Mangu Local Government Area, Plateau State. It was incinerated into ash in a furnace at temperature of up to 5000C for about 2 hours after which it was allowed to cool and thoroughly ground. It was then sieved through 75mm sieve as required by BS 12 (1990) and was used for this study.
Characterization of the lateritic Soil
Soils have peculiarities, they vary in properties. In other words, no two soils can be similar in all properties but can behave alike in some cases. Therefore it is necessary to identify a soil and properly classify it to the group it belongs. This can be achieved by conducting preliminary tests on the natural soil. The following tests were conducted on the lateritic soil:
CHAPTER FOUR
RESULTS AND DISCUSSION
Presentation of Results
The properties of the lateritic soil and particle size curve are shown in Table 4.1 and Figure 4.1 respectively. The characterisation of the mineral contents of the soil is shown in Table 4.2 and Figure 4.2 and 4.3.
CHAPTER FIVE
MODELLING AND OPTIMIZATION BAGASSE ASH CONTENT
Cost Analysis for the Stabilized Matrix
Practically speaking, little or no value has been attached to neither bagasse residue nor its ash because of its low demand. In the markets where sugar cane is sold and sugar factories, the bagasse residues are littered around the surroundings without much value. Definitely as the awareness of its usefulness increases, the demand will rise and the value/cost shall equally rise. It is therefore necessary to attach cost to the bagasse ash in order to make this work meaningful. The market prices or cost of the other materials at the time of this analysis should also be considered for appropriate basis for comparison. The bagasse ash, cement and the optimum moisture content were all measured as a proportion of the weight of the dry soil. Therefore using 100 grams of dry soil as a reference weight, the corresponding weights of cement, bagasse ash and water could be determined and their unit cost could be determined.
CHAPTER SIX
CONCLUSIONS AND RECOMMENDATIONS
Conclusions
After the investigation into the effects of bagasse ash on the properties of a reddish-
brown lateritic soil classified to be A-6(2) in the AASHTO rating and SC (Clayey Sand) in the Unified Classification System, the following conclusions were drawn:
- The lateritic soil contains non-problematic clay minerals and thus would be non-swelling.
- The bagasse ash has been confirmed to be a good pozzolana or
- The increase in bagasse ash content increased the optimum moisture content but reduced the maximum dry density of the cement-stabilized lateritic
- The increase in cement content increased the optimum moisture content and maximum dry density of the lateritic soil treated with bagasse ash and
- The increase in bagasse ash content improved the strength properties of the cement-stabilized
- The lateritic soil treated with bagasse ash and cement satisfied the requirement to be as sub-base of road
- The optimum content for bagasse ash and cement for the lateritic soil to be used as Sub-base of a roadwork is 14.03% and 4.52% respectively by the weight of dry soil for an economic mix while the optimum moisture content for the economic mix is 22.46%..
- The cost of material of stabilizing with the economic mix is 39.50 kobo for stabilizing 100 grams of lateritic soil as against 43.52 kobo for stabilizing with only
- The classical optimization was preferred over Scheffe’s simplex regression method for optimization in soil
Recommendations
The soil treated with bagasse ash and cement could only satisfy the requirement for sub- base of road work. However, 8% and 20% of cement and bagasse ash respectively by the weight of the dry soil could be considered for the base of the local light-trafficked roads.
Soils have perculiarities and variations in engineering behaviour with regards to their response to the addition of cement and other admixtures. In other words the results and observations are only exclusively recommended for lateritic soil deposit in Ndoro in Ikwuano local government area of Abia State. This study had in no doubt shown that the cement requirement for road work could be substantially reduced to optimum level and partially replaced by bagasse ash for road work to reduce the cost of materials. Ultimately, the design, construction, maintenance and re-building of low- cost roads would be very possible in the environs. These have already been in use in most developing countries especially in Asia; Nigeria could also tap into these potentials for the provision of road networks. Furthermore, Federal government has been projecting for vision 2020 and Millennium Development Goals (MDG). This could be one way of ensuring that they are achieved as projected. This is possible because if low-cost roads are being provided and adequately maintained to reach most rural farmers even in the hinter-land that are hitherto cut-off from transporting their agricultural products to the urban dwellers. It would assist in ensuring the availability of food and raw materials for the small and medium scale industries which enhance the socio-economic relationship between the urban and rural.
For further study, this kind of cost benefit analysis should be extended to other soil deposits and with various admixtures like rice husk ash, sugar-cane straw ash, palm kernel husk ash and so on because they are all pozzolanic in nature. These admixtures are readily available in the country in large quantities and could even constitute environmental problems if they are not properly handled. This study would be with a view of finding the one that is the most effective admixture and of lowest cost in order to maintain the cost of road work very low.
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