Influences of silicate modulus and alkali content on macroscopic properties and microstructure of alkali-activated blast furnace slag-copper slag

The stacking of copper slag (CS) has led to the resource wastage and environmental issues. Utilizing CS as a green precursor in the production of alkali-activated materials (AAMs) offers a promising avenue for sustainable resource usage. To obtain a deeper understanding and enhance its practical application, the effects of silicate modulus and alkali content of water glass (WG) on the performances of alkali-activated blast furnace slag-copper slag (AAS-CS) are systematically investigated though the fluidity, setting time, hydration heat, compressive strength and drying shrinkage rate. Additionally, the microstructure is characterized using nuclear magnetic resonance (NMR), X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR) and scanning electron microscope (SEM), respectively. When the alkali content is a constant of 6.0 wt%, the compressive strength and drying shrinkage rate initially increases with increasing silicate modulus, but eventually decrease beyond a certain threshold. At a given silicate modulus of 1.5, the compressive strength and drying shrinkage rate firstly increases and then decrease as increasing the alkali content from 4.0 wt% to 8.0 wt%. The microstructure analyses reveal that the suitable silicate modulus and alkali content promote the dissolution of precursors to form C-A-S-H gels. The M1.5N6.0 sample has a relatively tight microstructure, which benefits to the development of compressive strength, but increases the capillary stress. Therefore, the M1.5N6.0 sample has the highest 28-day compressive strength of 71.7 MPa and the largest 182-day drying shrinkage rate of 0.1532 %. •Experiments address effects of silicate modulus and alkali content on the performances of AAS-CS.•Suitable silicate modulus and alkali content can promote the hydration degree of AAS-CS.•M1.5N6.0 sample has the highest 28-day compressive strength of 71.7 MPa•The largest drying shrinkage rate of 0.1532 % is observed in M1.5N6.0 sample.