ABSTRACT
Black cotton soil classified as an A-7-6 (24) soil on AASHTO classification collected from new Marte area of Borno state was modified with up to 4% cement and LBWA up to 8% by weight of the soil. The effect of locust bean waste ash (LBWA) on the cement modified soil was studied with respect to particle size distribution , Atterberg limits, compaction characteristics and shear strength parameters using three 3 compactive efforts namely, British Standard light (BSl), West African Standard (WAS), and British Standard heavy (BSh). Statistical analysis was then carried out on results obtained from the test conducted to determine the significant difference (i.e., p < 0.05) in the various soil - cement mixes using a two – way analysis of variance (ANOVA) with the Microsoft Excel Analysis Tool Pack Software. Analyses of the results of the soil-cement mixtures considered indicate increase in particle sizes, increase in the liquid limit and decrease in the plastic limit with corresponding increase in plasticity index, increase in maximum dry density (MDD) with increase in optimum moisture content (OMC) as well decrease in cohesion with increasing angle of internal friction all with higher locust bean waste ash content. The result also showed that the modified soil met the requirement of the Nigerian General Specification of not more tha
n 35% passing No. 200 sieve when used as a sub grade material in road construction. An optimal blend of 4% cement / 8% LBWA is recommended for the modification of black cotton soil.
CHAPTER ONE
INTRODUCTION
1.1 Preamble
Geotechnical engineers are often faced with the problem of constructing road
beds on soil which do not have adequate strength to support the wheel loads imposed upon them either in construction or during the service life of the pavement. It is sometimes necessary to treat these soils, termed expansive soils to give a stable sub-grade or working platforms for the construction of the pavement. Treatment of soil are generally classified into two processes: soil modification or soil stabilization. The purpose of sub-grade modification is to provide a working platform for construction equipment, while sub-grade stabilization is meant to increase the strength and durability of the soil.
1.1.1 Black cotton soil
Expansive soil can be found almost any where in the world but they are basically confined to semi arid regions of the tropical /temperate zones. These areas are usually characterized by marked dry and wet seasons with low rainfall, poor drainage and exceedingly great heat. The precipitation is such that the annual evaporation exceeds the precipitation (Chen, 1988).
Two groups of parent rock materials have been associated with the formation of expansive soils. The first group comprises sedimentary rock of volcanic origin, which can be found in North America, South Africa and Israel (Ola, 1978). The second group of parent materials are basic igneous rocks found in India, Nigeria and South Western U.S.A (Plait, 1953). Tropical black clays are formed by weathering (Morin, 1971).
