Application of Suitable Admixtures (Lime and RHA) for Improvement of Pavement Subgrade

Abstract

Abstract
The quality of a pavement depends on the strength of its sub-grade. The present investigation has been carried out with easily available materials like lime and rice husk ash mixed individually and in combinations with different proportions. The different percentages of lime with respect to weight of dry soil were 2%, 4%, 6%, 8% 10% and for rice husk ash (RHA) were 3%, 6%, 9% and 12%. In each case the stabilized soil was compacted at optimum moisture content (OMC). In each case California Bearing Ratio (CBR) tests and in case of compaction at OMC Unconfined Compressive Strength (UCS) tests were performed. The effect of curing on UCS samples upto 180 days with the intervals of 30 days was also studied. It was found that CBR of original soil improved from 4.25% to a maximum value 28.25% when mixed with combination of 6% lime and 9% rice husk ash (RHA) under unsoaked conditions and from 3.5% to 29.82% when mixed with a combination of 6% lime and 6% rice husk ash (RHA) with respect to dry weight of soil under soaked conditions at optimum moisture content (OMC). The unconfined compressive strength (UCS) of original soil was improved by 253% when mixed with 6% lime and 6% rice husk ash (RHA).However the maximum value of UCS is attained by a value of 285% when mix proportion of 4% lime and 9% rice husk ash. Based on the laboratory test results correlations have been developed between California Bearing Ratio (CBR) at optimum moisture contents as function of different soil parameters by multiple linear regression models. To gain an insight into the reasons of strength increase by identifying the microfabric structure of soil and soil-lime-RHA mixes, semi quantative analysis with X-ray diffraction (XRD) and X-ray fluorescence (XRF) were conducted. The interpretations of results of XRD and XRF tests have clearly indicated that change in strength between lime and rice husk ash admixture occur due to change in silica and mica contents. It is concluded from this study that desired CBR and UCS values may be obtained on mixing a limited quantity of lime with soil when rice husk ash is also used as an auxiliary stabilizer making the mix cost effective.
Keywords: pavement, soil, lime, RHA