Effect of calcium carbide slag on the durability of alkali-activated ground granulated blast furnace slag-fly ash cementitious system

In this paper, alkali-activated composite cementitious materials were prepared by using calcium carbide slag, ground granulated blast-furnace slag (GGBS), and fly ash as raw materials, and a combination of sodium hydroxide and sodium silicate solutions were used as alkali activators of binders. The drying shrinkage, resistance to chlorine ion permeability, sulfate resistance, and mechanical properties of GGBS-fly ash cementitious system with different contents of calcium carbide slag were investigated. In addition, the changes in hydration products were also analyzed by X-ray diffraction (XRD). The results show that: when the content of calcium carbide slag instead of fly ash or GGBS is gradually increased, the drying shrinkage of the composite cementitious material decreases dramatically, the compressive strength and flexural strengths corrosion resistance coefficient increase first and then decrease, the compressive strength corrosion resistance coefficient decreases weakly. The primary hydration products of the composite cementitious material with varying calcium carbide slag content are calcium silicate hydrate (C-S-H) and calcium aluminosilicate hydrate (C-A-S-H) and these products remain stable under sodium sulfate erosion. Overall, the optimal properties were achieved with 3% calcium carbide slag replacing fly ash, which exhibits a 28 d drying shrinkage of 9672 με, an electrical flux of 2868 C, a compressive strength of 67.3 MPa after 120 d of full immersion in sodium sulfate, a flexural strength corrosion resistance coefficient of 1.21, and a compressive strength corrosion resistance coefficient of 1.02.