Suitability of Gypsum and Crushed Waste Brick Mix for Stabilization of Weak Subgrade Soil

Abstract

Expansive soil is one of the most abundant soils in Ethiopia, which mostly causes significant damage to structures such as buildings, roads and bridges due to their swellshrink effect. In the area of expansive soil and scarcity of suitable construction materials, upgrading the locally available materials is one of best alternative ways. Soil stabilization by adding additives is one of the methods of upgrading substandard materials. Therefore this study assessed the suitability of gypsum and crushed waste brick mix for stabilization of expansive soil to use as a road subgrade preparation. Expansive soil sample was collected from along Mettu-Burusa road and was investigated. Accordingly, expansive soil was stabilized with the mix of crushed waste brick and gypsum material proportion of 0%, 10%, 20%, 30%, 40 % and 0%, 2%, 4%, 6%, 8% respectively by weight of the total mix and laboratory tests such as Moisture Content, Grain size distribution, Atterberg Limit, Free Swell, Free Swell Index, Free Swell Ratio, Specific Gravity, Compaction, CBR and CBR-Swell are carried out to assess the alteration in its strength characteristics and index properties. The subgrade material quality improved from A-7-5 to A-2-4 at combination 30% of crushed waste brick and 6% of gypsum with expansive soil. By the addition of stabilizer material to expansive soil the least plasticity index value obtained was 9.030 % and the CBR increased to 10.686% from initial CBR value at the percentage of 30% brick and 6% gypsum. The OMC and MDD was increased to 29.200% and 1.480g/cm 3 respectively and the free swell, free swell index, free swell ratio was decreased to 18%, 16.830%, 1.168 respectively and CBR-Swell decreased to 1.370%, from the initial untreated soil test at percentage of 40% crushed waste brick and 8% gypsum mix with expansive soil. Based on the laboratory test results, it shown that the mixture of 30% of crushed waste brick and 6% of gypsum was the optimum combination material for stabilization of expansive soil to comply with the required technical specification specified in AASHTO. Treating expansive soil with the mix of crushed waste brick and gypsum respond and exhibited an improvement on its engineering properties including reduction in plasticity, increased strength and compaction characteristics