Impact of curing on behaviour of basaltic expansive clay

Abstract

Lime stabilisation is a commonly used method for improving the properties of expansive clay subgrades around the world. This paper investigates the effect of curing on the behaviour of lime-stabilised basaltic expansive subgrade. The effect of the presence of low levels of organic material in the surface clay on change in pH of the mixture is also investigated. This leads to a better understanding of the impact of curing duration on the process of lime stabilisation when dealing with these clays. In this study, Braybrook and Whittlesea (a western and a northern suburb of Melbourne, Australia) expansive clays were stabilised using different percentages of hydrated lime. Physical properties of untreated samples and those treated with 2%, 3%, 4%, 6%, and 8% lime were evaluated. A suite of tests was conducted to investigate the behaviour of the stabilised basaltic expansive clay over the curing period and to find the optimum lime content (OLC). These tests included pH concentration at various curing periods (at 1.5 h and at 7, 28, and 57 days), Atterberg limit, linear shrinkage (LS) strain (without curing), swelling potential, and unconfined compressive strength (UCS) (under curing periods of 7 and 28 days). Furthermore, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were conducted on Braybrook soil to investigate the mechanism of soil–lime reaction. The suitability of Eades and Grim [1966. A quick test to determine lime requirements for lime stabilisation. Highway Research Record, 139, 61–72] method in determining OLC is also discussed. Test results of these soils indicated that the longer the curing time, the larger the drop in pH concentration. While the swelling potential results suggest an OLC of 4% (for Braybrook) and 6% (for Whittlesea), UCS tests, plasticity indices, and LS suggest an OLC of 6% for Braybrook soil, while it is about 8% for Whittlesea soil according to UCS tests. However, according to the Eades and Grim (1966) procedure, OLC is about 2.64% and 4% for Braybrook and Whittlesea soils, respectively. This paper suggests a modification of Eades and Grim (1966) method to measure the OLC for basaltic expansive clays to take into account the dropping of pH concentration during curing. The mechanism of lime stabilisation and the analysis of the above tests were the major factors to establish this modification. This modification depends on measuring pH concentration at different lime contents and curing periods. The results contribute to a better understanding of the impact of curing and low levels of organic matters on the stabilisation of expansive clays, which can ultimately lead to a simplified procedure in the determination of OLC.