Stabilization Of Black Cotton Soil Using Bagasse Ash Mixed With Cement For Subgrade In Road Construction: A Case Study On Kafta Humera

Abstract

Expansive soils occurring in arid and semi-arid climate regions of the world cause serious problems on civil engineering structures. Such soils swell when exposed to water and shrink when they dry out. Several attempts are being made to control the swell-shrink behavior of these soils. The swell and shrinkage distinctiveness of expansive soil causes significant damage to structures such as buildings and pavements. The above problems are extensively occurring in Ethiopia. The aerial coverage of expansive soils in Ethiopia is estimated to be 9.9 million hectare. Since most soil which is found in Humera town are plastic clay soils. These clays are a consequence for expansive and unstable soil. As a result, they make pavement structure failure. The general objective of this research was to assess on stabilizing black cotton soil using bagasse ash mixed with cement for sub grade in road construction. In this study moisture content, Atterberg Limits testing, particle size distribution, classification, free swell index, specific gravity, compaction and uncured and 3, 7 and 14 days cured CBR was determined. The research design was followed the experimental type of study which begins by collecting samples. The sampling technique used for this research was a purposive sampling which is non– probability method. Two black cotton soil samples were taken from three test pit for the study by observation and free swell index tests at a depth of 1.50 m to remove organic matter. Bagasse ash was taken from Arjjo Dedessa sugar factory. The result of physical properties of Adiremets – Adihidi – Beahker Road project soil sample has plastic index 53.77%, free swell index 80%, and CBR value 0.98 % for uncured and 1.14%,1.37% and 1.72% for 3,7 and 14 days cured soil respectively. Similarly, Humera Airport soil sample has plastic index 63 %, free swell index 100 % and CBR value 0.81% for uncured and 1.11%, 1.30% and 1.65% for 3, 7 and 14days cured soil sample respectively. Since both the given soil samples were found with high degree of expansion, stabilization was made with different mix-ratio. As the amount of cement ratio increases CBR strength also increase but amount of cement decreasing with increasing bagasse ash did not increase strength. 8% cement + 2% bagasse ash is an optimum ratio which has the plastic index 8%, free swell index 20%, and CBR value 10.7 % for uncured and 20.48%,28.93% and 40.95% for 3,7 and 14 days cured soil respectively. Similarly, Humera Airport soil sample has plastic index 12%, free swell index 23% and CBR value 10.1% for uncured and 19.83%, 28.6% and 38% for 3, 7 and 14days cured soil sample respectively. All the laboratory result was compared with ERA specifications. Additional curing time effect on all geotechnical laboratory tests should be performed. The high amount of bagasse ash should add to cement to get relevant strength and to reduce the cost of highway construction