Strength of Extreme Soils Blended with Fly Ashes for Pavement

Abstract

The investigation of the present work brings out the effect of Raichur Fly Ash (RFA) and Nyveli Fly Ash (NFA) on California Bearing Ratio (CBR) of two extreme soils, Black Cotton soil and Red earth. CBR of soil fly ash mixtures assume great importance in their use for road construction. CBR are modified depending on the soaking condition. Thus the CBR of soil fly ash mixtures are determined as compacted and also in soaked condition. CBR of fly ashes under un-soaked conditions exhibit higher values because of additional resistance from capillary forces, for instance when 20% of RFA is added to black cotton soil under Unsoaked condition, blend has shown CBR of 10.38% as found in results. In presence of water fly ashes loose capillary forces and gives lesser CBR, where blend has shown CBR of 4.56% for addition of same quantity of RFA. Same additions when it is made to Red earth, the corresponding results are 11.74% for Unsoaked and 4.74% for soaked conditions. In cases of fly ash with calcium, they generate cementitious gel and impart strength to mix, which increases the CBR even in soaked condition [1]. Addition of cement to RFA and lime to NFA, the resistance of blends increases. CBR of soils with RFA exhibits pronounced peaks at fly ash contents of 20% and 80%. This is due to predominance of skeleton of soil and fly ash respectively. The CBR of soil with NFA addition further increases with soaking. CBR of soil with NFA addition increases continuously with fly ash content. The results reveal that when same 20% NFA is added to soil, the CBR of soil in unsoaked condition is 11.46%, whereas for soaked condition it is 23.62%.