THE ENGINEERING CHARACTERISTICS OF BLACK COTTON SOIL TREATED WITH CORN STRAW ASH.

Abstract

Black cotton soils (BCS) are found in extensive quantities in the North – East region of Nigeria specifically in
the northern parts of Adamawa State and southern parts of Borno State. This soil expands while it gets wet and shrinks as the
water dries out. On account of this high volumetric changes they are not directly suitable for construction. The excessive
swelling and shrinkage are sequel to the presence of fine particles of clay. Swelling and shrinkage of soil often results in
differential settlement of the structure. Black cotton soils must therefore be treated by using suitable admixtures to stabilize it
for use in civil engineering works. In this research work, stabilization of black cotton soil is done by using Corn Straw Ash
(CSA) as an admixture. The CSA reacts with clay particles from the black cotton soil to form a material of higher strength.
The physical and chemical properties of the soil were obtained. Other tests such Atterberg’s limits, California Bearing
Ratio(CBR), Unconfined Compressive Strength(UCS) were carried out at different percentage contents of CSA: at 0%, 4%,
6%, 8% and 10%. From the test results, it is observed that optimum value of CBR and UCS are at 8% of the ash. At this
percentage of the additive the following improvement occurred in the black cotton soil; CBR improved from 4.5% to 11.3%,
UCS 107.5KN/m2
to 140.5KN/m2
and plasticity index decreased from 24% to 11.2%. It is concluded that CSA has a great
potential in the improvement of the mechanical properties of black cotton soil.