Water Immersion-Induced Strength Performance of Solidified Soils with Reactive MgO—A Green and Low Carbon Binder

Abstract

Abstract Although portland cement is widely used for soft ground improvement, there are significant environmental impacts associated with its production. Thus, the reuse of industrial by-products is encouraged to develop environmentally friendly binders. The soils solidified with reactive magnesium oxide (MgO)—a green and low carbon binder—are subjected to water immersion for different periods of time, and later, the unconfined compressive strength tests are performed on them. The water stability of nonsolidified and MgO-solidified soils is evaluated by visual examination and strength evaluation. A detailed comparison of strength between MgO-, MgO plus fly ash-, and cement-solidified soils is performed, and the test result demonstrates the reinforcing effect of fly ash addition and the superiority of reactive MgO over cement in strength optimization. The image analysis suggests three typical failure modes of tested samples, i.e., shearing failure, lateral bulge failure, and taper failure. The failure modes are closely related to the compressive strength levels. The data indicate that the power function and linear function can describe satisfactorily the correlations of compressive strength against failure strain and compressive strength against the deformation modulus. The microstructural analysis, especially, reveals that the main hydration products responsible for strength amelioration are magnesium hydroxide (Mg(OH)2) and calcium-silicate-hydrate (C-S-H) gels for MgO and cement-treated soils, respectively. Further research should be systematically performed on MgO plus fly ash-solidified soils to investigate the physico-chemical reactions that potentially occurred, although Mg(OH)2 and M-S-H are primarily detected in reactive MgO-activated fly ash paste. To summarize, the environmental and economic benefits can be expected from replacing portland cement with reactive MgO-bearing binders for soil solidification.