Development and evaluation of physical and mechanical properties of alkali-activated multi-component composite grouting materials

Using mineral powder, fly ash and cement as the basic three-component composite system, machine-made sand and gravel powder and expansion agent are introduced to prepare five-component composite grouting materials. The water-binder ratio, stone powder content, the water glass modulus, the alkali content, the water-cement ratio, and machine-made sand and gravel powder content were studied for the physical and mechanical properties of alkali-activated multi-component composite grouting materials. The law of influencing factors and the optimal parameters of each factor were determined according to fluidity, setting time, compressive strength, and drying shrinkage. The optimal values of water glass modulus and alkali content are 1.0 and 6%, respectively. Increasing the water-binder ratio significantly improves fluidity, but results in a substantial delay in setting time and a decrease in strength. Therefore, it is not advisable to exceed a water-binder ratio of 0.6. Furthermore, the stone powder content should not surpass 10%. The hydration process of alkali-activated materials mainly includes crystallization nucleation and growth, phase boundary reaction and diffusion. Three types of expansion agents, CaO, MgO and SC (the mixture of calcium sulfoaluminate and calcium oxide), were selected, and four levels of 0%, 4%, 8%, and 12% were set, including a total of 9 mix ratios besides the benchmark group. The effects of expansion agents on the fluidity setting time, compressive strength and volume stability of composite grouting materials were discussed. The addition of an expansion agent proves effective in reducing drying shrinkage, with the sequence of effectiveness as follows: CaO expansion agent > MgO expansion agent > SC expansion agent. The optimal content of CaO expansion agent is found to be 8%, leading to a remarkable reduction in 28 d shrinkage.