Insights on stabilization of marly soils through alkali activation with the use of slag and metakaolin as additives

Abstract

The most common binders used for soil stabilization are ordinary Portland cement (OPC) and lime. However, due to the high carbon footprint of cement production recent research efforts focus on the use of other eco-friendly binders. In this context, the present study aims to assess the effect of the use of slag or metakaolin as precursors during alkali activation for the stabilization of marly soils. The slag (SL) used in the present study derives from an electric arc furnace during the pyrometallurgical processing of laterites for the production of ferronickel (FeNi) at 1450 °C, while metakaolin (MK) is produced from the calcination of kaolin at 750 °C. The alkali-activating agent used is a mixture of NaOH and Na2SiO3 solutions.The effect of various operating parameters, including the molarity of NaOH (2–8 mol L−1) which affects the H2O/Na2O and SiO2/Na2O ratios present in the activating solution, curing temperature (25–80 °C), curing period (0–24 h) and ageing period (7–28 days) on the compressive strength of the produced alkali activated materials (AAMs) was investigated. The effect of calcination of marly soil at 900 °C was also briefly explored during alkali activation at low temperature. Mineralogical analysis (XRD), fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) are used to elucidate the microstructural characteristics of the produced specimens and the reactions that take place during the synthesis of AAMs.The experimental results indicate that the use of slag or metakaolin as precursors favors the stabilization of marly soils through alkali activation, while the produced specimens acquire compressive strength varying between 15 and 23 MPa. Higher curing temperature (40–80 °C) and longer ageing periods (28 days) are the factors that have a more clear beneficial effect on the compressive strength acquired by AAMs produced from blends of marly soil and slag. On the other hand, specimens produced from blends of marly soil and metakaolin acquire higher compressive strength values after curing at lower temperature. Finally, calcination of marly soil at 900 °C has a rather small beneficial effect on the compressive strength of the produced AAMs.