Abstract:
The strength of the road subgrade for, which mostly causes significant damage to structures such as buildings,
roads and bridges due to their swell-shrink 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 Ilubabora zone 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/cm3
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. 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
