The strength, reaction mechanism, sustainable potential of full solid waste alkali-activated cementitious materials using red mud and carbide slag

Alkali-activated cementitious material (AACM) is a green building material which effectively utilizes industrial solid wastes, such as red mud (RM), ground granulated blast furnace slag (GGBS). However, there are problems with using conventional alkali activators (NaOH, Na2SiO3), including strong corrosivity and high cost. In order to solve this problem, this study prepares full solid waste cementitious materials (FSWCM) by activating RM and GGBS using carbide slag (CS) instead of traditional alkali activator. Based on the response surface method (RSM), the effects of RM content, CS content and water-binder ratio on the performance of FSWCM were studied. The microstructure changes of FSWCM with different RM contents were analyzed by XRD, TG, FTIR and SEM-EDS. The results showed that the optimized content of RM and CS was 40 % and 20 % respectively, and the 28d compressive strength reached 14.11 MPa, which met the requirements of road base materials. The regression model established by RSM had high accuracy and could accurately predict the performance response values. The alkaline environment created by CS-RM facilitated the decomposition of active components in GGBS, resulting in the formation of a considerable amount of C-(A)-S-H gel via polycondensation. With the increase of age, Na+ dissolved in RM replaced Ca2+ in C-A-S-H to form N-A-S-H gel. The hydration products N-A-S-H, C-(A)S-H and CaCO3 were intertwined to form a stable and dense three-dimensional network structure, which provided excellent mechanical properties. Sustainability analysis shows that FSWCM has significant advantages in cost control and environmental friendliness compared with AACM.