Use of recycled concrete aggregates in stabilization of black cotton soil

Abstract

The long-term performance of a pavement structure depends on its structural integrity and the stability of its underlying soils. The properties of black cotton (BC) soils are known to adversely affect the performance of pavement. BC soil is creating a lot of problems in constructing the pavements on it because of its low California bearing ratio (CBR) and high swelling potential behavior. Black cotton soil possesses poor strength, high swelling and shrinkage behavior on exposure to moisture. Pavements on BC soil require stabilization. Soil stabilization is a process utilized for improving the properties of undesirable weak soil.  Stabilization of subgrade soil by chemical, thermal or mechanical techniques is very common practice and too expensive. Therefore, in this study, an attempt has been made to stabilize the BC soil subgrade by recycled concrete aggregate (RCA). The RCA are the waste aggregates obtained from demolition of concrete structure buildings, road, and bridges. The main aim of this study is to know the suitability of RCA waste as a stabilizer for BC soil in the construction of flexible pavements. In this investigation, properties of RCA and BC soil are evaluated, RCA is mixed in different proportions with the BC soil, and their influence on the CBR value and compaction curve are studied. Seven mixes (100% BC soil, 90% BC soil + 10% RCA, 80% BC soil + 20% RCA, 70% BC soil + 30% RCA, 60% BC soil + 40% RCA, 50% BC soil + 50% RCA, 40% BC soil + 60% RCA) are tested for CBR value in order to find the proportion which gives maximum CBR value. Based on the results, it is observed that for the BC soil used in this study, mix containing 60% BC soil and 40% RCA is the suitable mix proportion for the stabilization. For this proportion of mix, the CBR value increased from 3.53% to 11.2%. This accounts to 3.2 times increase in the CBR value, whereas the optimum moisture content (OMC) decreased from 27% to 22% and maximum dry density (MDD) increased from 1.22 gm/cm3 to 1.45 gm/cm3. Hence 60% BC soil and 40% RCA   can be used to stabilize the given soil.