Performance of cementitious materials prepared with magnesium slag and concrete slurry waste

Concrete slurry waste (CSW) and magnesium slag (MS) have similar compositions to cement, and both pose challenges for conventional reuse. Considering the carbonation activity of MS due to the presence of γ-C2S, MS and CSW were utilized to produce a type of low carbon cementitious material through CO2 curing. The carbonation products and microstructure of the mixture pastes were analyzed using XRD, XPS, FTIR, SEM, MIP, TG-DSC and NMR. The mixture pastes, comprising 26.6% CSW by weight, demonstrated robust strength, achieving a compressive strength of 52.5 MPa and a flexural strength of 10.7 MPa, with a calculated CO2 absorption rate of 11.26%. CSW effectively influenced the CO2 absorption rate in mixture pastes, actively participated in their matrix structure construction, and contributed to the formation of C-(A)-S-H gel. Interwoven carbonation products, such as SiO2-gel, amorphous calcium carbonate, calcite, etc., contributed to the increase in strength. The stability of the mixture pastes was demonstrated by the sustained increase in compressive strength after curing in water for 56 days, which acted as a softening coefficient with a value higher than 1.0. After being cured in water, the hydration of residual silicate minerals in the specimen following carbonation, combined with the reaction of CO32- released from calcium carbonate with gels, including C-S-H and C-(A)-S-H, promoted the evolution of strength. Water curing promoted the development of finer pores and resulted in a denser matrix structure within the slurries.