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/cm<sup>3</sup> 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.
Highlights
Worldwide the availability of natural construction materials within reasonable hauling distance is one of the major factors that have a direct impact on the investment cost of road projects
The laboratory tests conducted for this study were moisture content, specific gravity, grain size analysis, Atterberg limits, free swell test, free swell index, compaction, California bearing ratio (CBR) and CBR swell tests
From the study the following findings are deduced: The properties of natural sub grade soils was expansive clay soil, Based on the AASHTO (American Association of State Highway Transportation Official) soil classification system, the original soil samples was A-7-5 and the group index was 38, Based on the AASHTO soil classification was grouped under poor subgrade soil, The sub grade soils considered for this study have a very low load bearing capacity and high swelling potential which makes the soils unsuitable for sub grade without improvement, The specific gravity of original expansive soil was 2.650
Summary
Worldwide the availability of natural construction materials within reasonable hauling distance is one of the major factors that have a direct impact on the investment cost of road projects. Natural construction materials are either not available or do not fulfill the quality requirements of road construction materials. Problems associated with these construction materials have been reported in Africa, Australia, Europe, India, and South America, the United States as well as some regions in Canada. In many areas of the tropics especially Africa and India, tropical expansive soils often known as black cotton soils are the major problematic soils. These soils show very strong swelling and shrinkage characteristics
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