Study on Hydration and Hardening Performance of Coal Gangue-Steel Slag-Cement Composite Cementitious Material

In this paper, coal gangue powder (CGP) was used to replace 30% of the cement weight. The dosage of steel slag powder (SSP) was 5%, 10%, 15%, 20%, and 25% of the coal gangue weight. The CGP-SSP-cement mortars and pastes were prepared. The compressive and flexural strengths, hydration heat, X-ray diffraction (XRD), thermogravimetric analysis (TGA-DTG), pore structure (MIP), electric flux, and capillary water absorption were examined. Results displayed that the detrimental effects of single-doped CGP were reduced by adding SSP to a single 30% calcined coal gangue powder (CCGP). Compared with the single-doped 30% SSP, the compressive strength value prepared by 10% CCGP and 20% SSP at 28 days was 15.21% higher. Compared with the single-doped 30% SSP, the flexural strength value prepared by 15% CCGP and 15% SSP at 28 days was 15.78% higher. When 15% CCGP and 15% SSP were combined, the mortar's electric flux was 31.71% lower and the capillary water absorption was 9.48% lower compared with the single-doped 30% SSP. The microscopic results showed more hydration products such as AFt and CH, were produced under the synergistic effect of CCGP and SSP. The number of macropores was reduced compared with CCGP or SSP alone.