Strength characteristics of modified black clay subgrade stabilized with cement kiln dust

Abstract

This paper presents the results of a laboratory study in which the strength properties of black cotton soil (BC soil) subgrade modified with quarry fines (QF) were stabilized with cement kiln dust (CKD). The experimental program included Atterberg limits, compaction and unconfined compression testing of BC soil treated with QF at a constant dosage of 10% stabilized with CKD for dosages in the range 0–16% on dry weight basis. Soil mixtures were compacted with British Standard Light energy, and specimens for unconfined compression testing were prepared at predetermined optimum moistures and cured for 28 days. Test results showed that the studied soil which classify as A-7-6 (20) group in American Association of State Highway and Transportation Officials classification system has liquid limit and plasticity index of approximately 85.0 and 50.5%, respectively, as well as a free swell of 65.0%. The application of QF together with the varying percentages of CKD lowered these parameters to values compatible with specification for subgrade layers prescribed by Nigerian General Specification for Roads and Bridges. While the addition of QF caused an increase in the maximum dry unit weight of the soil, the introduction of CKD resulted in the reduction of the maximum dry unit weight of soil mixtures. On the other hand, optimum moisture contents increased slightly following the treatments. Furthermore, both the unconfined compressive strength (UCS) and the stiffness moduli (initial tangent, Ei, and secant, Esec, evaluated from the experimental stress–strain responses) of soil mixtures increased significantly as a consequence of the joint effects of quarry fines and CKD treatment producing soil mixtures with desired values for performance in road pavement subgrades.