CHAPTER ONE
1.0     INTRODUCTION
The search for alternative binder or pozzolanic material has become a challenge to national development.  Potential of laterite soil as a reliable and durable construction material is highly locally available and has been one of the major building materials for a long time. One of the various soil types that occur in the tropic and sub-tropic laterite is one of the commonest types and is of special interest in building and road constructions. Laterite soils are highly weathered soil which contains large but extremely variable proportion of iron and aluminum oxides well as quartz and other minerals.  AASHTO classified soils into seven groups. A – 1 to A – 7. According to the AASHTO subgrade classification system, residual soils are typically classified in the A – 2 category (AASHTO Designation: M 145 – 87).  The glacial soil found in the northern states can be classified as either gravel  (A – 1) sand (A – 2), Silts (A – 5) or silty clays (A – 6).  The coaster soils along the eastern seaboard and in the gulf area are largely sands and gravel.  Note, however, that within this region are extensive area of highly plastic clay (A – 7). According to Ola (1978) most lateritic soil for road fall within the A – 2, A – 6 and A – 7 group and lateritic soil have been found in the A – 3 and A – 5 group. Laterite is defined in Osula (1984) is a highly weathered tropical soil, rich in secondary oxide of any or a combination of iron, aluminum and manganese, manganese having been reported as a predominant element with combination with iron is some varieties of laterites notable those in India,  Nigeria laterite soil are derived from basic igneous, metamorphic and sedimentary rock and can be found in the sedimentary basin and over the basement complex area of the country (Durotoye 1983).  Laterite soil has been successfully used in various aspect of civil engineering construction project.  Laterite materials are employed in the construction of airports, runways, highways, earth fill dam, low cost building etc. Osinubi and Kate (1997) have described laterite soil as the most common pavement materials in the tropics and sub-tropics. Some laterite soil, like laterite clays required improvement on the engineering properties before they can be used in any form of construction due to the fact that these soil have high swelling potentials which caused problem in construction thereby making them not favourable when used for construction materials in their natural states.