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Properties of underlying soils and borrowed soil samples are some of the key factors that determine the performance rate of roads. Most of the underlying soils possess some characteristics that make them unsuitable for use. There are available agricultural waste products in most rural settlements which can be used to treat unsuitable soils. This research examined the use of corn cob ash (CCA) as an admixture to cement on some selected geotechnical properties of laterite soil. The choice of the A-7-5 class of laterite soil is due to its general rating as poor material for subgrade and other layers of road pavement by the classification system of the American Association of State Highway and Transportation Officials (AASHTO). Cement was gradually added to the soil sample in steps of 2% from 0% to 10% by weight of the soil sample and its effect on the plasticity of the sample was examined. The addition of cement performed optimally on the soil’s plasticity at 4% which was used to form different mixtures of cement and CCA having a total sum not exceeding 4%. The additives were added to the soil sample which was subjected to laboratory tests such as compaction, California bearing ratio (CBR) and unconfined compressive strength (UCS) compacted with the efforts of 596kN/m2 and 1192kN/m2. The combination of 2% cement and 2% CCA on the soil sample improved the plasticity index and UCS properties of the soil to its optimal level while 3-1 and 4-0 cement-CCA performed optimally for CBR and compaction respectively. Thus, it was concluded that CCA performed optimally with cement at a ratio varying between 4:0 to 3:1 total percentage not exceeding 4% of the weight of the soil sample.
Popoola et al. (Fri,) studied this question.