Experimental investigation on replacing cement by sintered limestone ash from the steelmaking industry for cement-stabilized soil: Engineering performances and micro-scale analysis

Abstract The enormous cement demand for soil stabilization intensifies the carbon footprint on the environment, which can be relieved by replacing cement with supplementary cementitious materials (SCMs). However, such application of common SCMs is limited by the availability and the reactivity of the materials. To deal with this issue, sintered limestone ash (SLA), a novel waste from the steelmaking industry, was investigated for the feasibility of replacing cement for soil stabilization. The SLA was first characterized by means of a laser particle sizer, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), thermogravimetry (TG) and X-ray fluorescence (XRF), and was revealed to process a certain hydration reactivity. To prepare the stabilized soils, the mass fraction of cementitious materials (i.e., cement and SLA) was controlled to 10% of the total dry mass of the solids, and the SLA was then used to replace the cement in mass fractions of 0%, 5%, 10%, 15%, 20%, 50%, 80% and 100%. Subsequently, unconfined compression test revealed that the unconfined compressive strength (UCS) of the stabilized soils were benefitted from an SLA replacement ratio of ≤20%, while they decreased substantially thereafter. Following the UCS test, the compactability and hydraulic conductivity of representative soil samples were investigated, while XRD, SEM-EDS, TG and mercury intrusion porosimetry (MIP) were employed for the micro-scale characterization and mechanism analysis. With increasing SLA replacement ratios, the compactability and hydraulic conductivity value of the stabilized soils were improved. The beneficial effects were produced by the enhanced formation of calcium aluminate hydrate (CAH) and Al2O3–Fe2O3–mono (AFm) phases, as well as the filling effect of high content CaCO3 of SLA, while the deteriorative effects were produced by the relatively low reactivity of SLA compared to that of cement. In addition, the SLA replacement promoted the formation of Fe-AFm, and the high CaCO3 content hindered the carbonation process of AFm phases, enhancing their stability.