Solidification of waste excavation clay using reactive magnesia, quicklime, sodium carbonate and early-age oven curing

Abstract

Kaolin production requires large amounts of excavation waste to be removed, with each tonne of kaolin recovered typically producing up to 9 tonnes of waste. This study introduced quicklime (i.e., CaO), reactive magnesia (i.e., MgO) and sodium carbonate, together with an early-age oven curing regime as a means of re-using kaolin excavation waste to produce more sustainable cementitious materials. The strength development of solidified clay samples was measured and later interpreted by pH tests, porosity measurement, Fourier-Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy-Energy-dispersive X-ray spectroscopy (SEM-EDX). Besides, the environmental impacts with respect to the production of additives for clay solidification were also calculated. The results indicated that the incorporation of CaO and MgO effectively solidified the clay with acceptable compressive strength (CaO group: 12.2 MPa; MgO group: 20.3 MPa after 28 days). Meanwhile, given the strength development of samples investigated in this study, the morphology of hydration phases could be possibly more important than their contents and sample porosity. Furthermore, with the introduction of 3 days of oven curing, MgO took advantage over CaO in clay solidification, which was attributed to the formation of fibrous crystals (i.e., nesquehonite) and fewer micro-cracks. Finally, from a perspective of ‘greenness’ and sustainability, MgO is a more favorable additive than CaO and PC in soil solidification.