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Reactive magnesia (MgO)-activated ground granulated blast furnace slag (GGBS) is a newly developed binder for soil stabilization/solidification. It can be used as an alternative of conventional hydraulic binders for the stabilization/solidification of heavy metal-contaminated soils. Acid rain exposure has been found to weaken the heavy metal immobilization in solidified/stabilized soils in the long term. However, very limited studies have been conducted to investigate the effect of acid rain on the physical and strength properties of GGBS–MgO-stabilized heavy metal-contaminated soils. In this study, GGBS–MgO-stabilized lead (Pb)-contaminated soils are subjected to the semi-dynamic leaching test using the simulated acid rain (SAR) as leachant, which has pH values of 2.0, 3.0, 4.0, and 5.0. Deionized water (pH 7.0) is also used for comparison. Dry density, soil pH, needle penetration depth, and unconfined compressive strength (qu) of the solidified/stabilized soils are measured after the leaching test. The results show that exposure to SAR yields reduction in qu and soil pH, whereas the needle penetration depth increases and dry density changes only marginally. The qu of the solidified/stabilized soils increases noticeably with increased GGBS–MgO content. It is also found that the stabilized Pb-contaminated soil exhibits lower qu than its clean soil counterpart. Furthermore, a quantitative relationship is proposed to correlate the normalized needle penetration resistance with the normalized qu. Finally, a multiple linear regression is performed to statistically reveal the dependence of soil strength on three independent variables, which are SAR pH, Pb concentration and binder content.

Ground granulated blast furnace slag (GGBS) is widely used to stabilize soils due to its environmental and economic merits. The strength and durability of reactive MgO activated GGBS (GGBS-MgO) stabilized lead (Pb)-contaminated soils have been explored by previous studies. However, the effects of simulated acid rain (SAR) on the leachability and micro-properties of GGBS-MgO stabilized Pb-contaminated soils are hardly investigated. This research studies the leachability and microstructural properties of GGBS-MgO stabilized Pb-contaminated kaolin clay exposed to SAR with initial pH values of 2.0, 4.0 and 7.0. A series of tests are performed including the semi-dynamic leaching tests using SAR as the extraction liquid, acid neutralization capacity (ANC), mercury intrusion porosimetry (MIP), and X-ray diffraction (XRD) tests. The results demonstrate that as the SAR pH decreases from 7.0 to 4.0, the Pb cumulative fraction leached (CFL) and observed diffusion coefficient (Dobs) increases significantly whereas the leachate pH decreases. Meanwhile, increasing the GGBS-MgO content from 12% to 18% results in the decrease of CFL and Dobs. Further decreasing the SAR pH to 2.0 results in the dissolution-controlled leaching mechanism regardless of the binder dosage. The differences in the leaching properties under different pH conditions are interpreted based on the cemented soil acid buffering capacity, hydration products and pore size distributions obtained from the ANC, MIP, and XRD tests, respectively.

The strength characteristics and hydration products of reactive magnesia (MgO)-activated ground-granulated blast-furnace slag (GGBS) cement and concrete have been extensively investigated in previous studies. However, very limited study has comprehensively investigated the impacts of drying–wetting cycle on the engineering properties of GGBS–MgO-stabilised soils. This paper presents details of a study dealing with the influences of drying–wetting cycle on the dry density, pH, unconfined compressive strength (qu) and secant modulus (E50) of GGBS–MgO-stabilised kaolin clay. For the purpose of comparison, the conventional Portland cement (PC)-stabilised kaolin clay is selected as a control sample. Several series of and drying–wetting durability and unconfined compression tests were conducted for the stabilised soils. The variations in dry density, mass loss, pH, qu and E50 with drying–wetting cycle are discussed. The results show that the GGBS–MgO-stabilised kaolin clay display higher dry density (~1–7%) and lower mass loss (~10–30%) than the PC-stabilised kaolin clay. The pH values and qu of the GGBS–MgO-and PC-stabilised kaolin clay decrease with the increase of drying–wetting cycle. When cured for 93–120 days under the controlled temperature of 20 °C and relative humidity of 95%, the GGBS–MgO-stabilised kaolin clay exhibits higher (~1.5 times) qu than the PC-stabilised kaolin clay. However, when the drying–wetting cycle exceeds forth, the GGBS–MgO-stabilised kaolin clay displays lower qu or E50 than the PC-stabilised kaolin clay. The measured soil pH has a good linear relationship with qu of the soils that experienced drying–wetting durability tests. Finally, the mechanisms underneath the gradual loss of qu or E50 with increasing drying–wetting cycle are discussed.