Study on optimization of mixing ratio and shrinkage property of alkali-activated ultrafine fly ash-slag mortar

Alkali-activated cementitious materials have received widespread attention due to their favorable mechanical properties and environmental benefits. However, there are fewer studies on the optimal mixing ratio of alkaliactivated ultrafine fly ash-slag (AAUS) mortar, and shrinkage cracking is a critical issue that hinders its further application. Based on this, the study used the response surface method (RSM) to optimize the mixing ratio of AAUS mortar, explored the effect of basalt fibers (BF) on the compressive strength and drying shrinkage of AAUS mortar, and finally analyzed the energy consumption and carbon emission of fiber-reinforced AAUS mortar. The experiment used X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques for microstructural characterization to research the microstructure and mineral phase changes of AAUS mortar. The results demonstrated that the 28d compressive strength of AAUS mortar reached its maximum when the substitution ratio of ultrafine fly ash (UFA) was 14.5 %, the alkali equivalent was 10.34 %, and the modulus of the activator was 1.6, based on the RSM; BF of appropriate length and volume fraction can productively improve the compressive strength of AAUS mortar and limit drying shrinkage; AAUS mortar with optimal mixing ratio can be sufficiently activated by alkali activator to construct a considerable number of C-(A)-S-H gels to establish a highdensity microstructure; the carbon emission of the B124 test group was reduced by 61.1 % compared with ordinary Portland cement (OPC) mortar.