Performance assessment of active soils stabilized with quarry dust and cement kiln dust admixture for use in the subgrade layer.
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Active soils, normally referred to as expansive soils are soils prone to changes in volume with changes in moisture content (shrink-swell behaviour) characterized by high swelling and shrinking nature hence poor subgrade characteristics. For such soils, a single additive might not be sufficient in stabilization and the use of combined stabilizers (one of the stabilisers in the combination compensates for the lack of effectiveness of the other in treating a particular aspect) is imperative. This project was aimed at assessing the physical and strength characteristics of active soils (that is, black cotton soils, BCS and red clayey soils, RCS) blended with a combination of cement kiln dust (CKD), a by-product of cement manufacturing process and the chemically non-active Stone Quarry Dust (SQD), a non-primary product from in quarry processes. The performance of both soils has been compared. The neat soil samples (red clayey soil and black cotton soil) were modified (blended with SQD and CKD) by varying proportions of the stabilizers. The soils were mixed with SQD in concentrations of 0%, 10%, 20% and 40% by dry weight of the soil and each of these was combined with varying proportions of CKD of 0%, 2%, 4% and 6% respectively by dry weight of the soil. The laboratory results were analyzed based on the effect of the additives in comparison with the engineering properties of the native and modified soils. This was achieved by conducting the following tests: free swell, sieve analysis, Atterberg’s limits, compaction and CBR tests. From the tests, it was observed that the BCS had a high plasticity index, high swelling potential and low bearing strength. The RCS also had a high plasticity index, medium swelling potential and low bearing strength as well. The addition of these stabilisers to both soils showed an increase in strength and reduction in the plasticity index of the neat soil sample. Furthermore, it was observed that RCS samples treated with the SQD-CKD combination generally showed a slightly better improvement (of the engineering properties) than the BCS samples treated with the samecombination. Further research is recommended on the clay mineralogy of the expansive soils and how it affects their suitability for subgrade construction as the additives are added.