Fly ash and granulated blast furnace slag are both bulk industrial solid wastes. Using these two raw materials to completely replace cement and prepare alkali-activated fly ash slag concrete (AAFSC) at room temperature can not only efficiently utilize industrial solid waste and reduce the carbon footprint, but also reduce the economic cost and technical difficulty of construction, which is of great significance for promoting the sustainable development of the concrete industry. In this article, the content of fly ash accounted for 80% of the total precursor (fly ash + slag), and a mixed solution of sodium silicate and sodium hydroxide was used as alkali activator to prepare AAFSC by curing at room temperature. The effects of alkali equivalent and activator modulus on compressive strength, impermeability, water absorption, and microstructure were systematically studied and compared with ordinary Portland cement concrete. The conclusions drawn were as follows. The 7-day compressive strength of AAFSC was lower than that of cement concrete, while its 28-day compressive strength was 104.86% to 131.94% of that of cement concrete. AAFSC exhibited excellent impermeability protection performance. The water absorption rate of AAFSC was lower, with A8M1 having a water absorption rate of 2.13%, which was only 60.86% of cement concrete. Through microscopic analysis, it was found that the alkali-activated fly ash slag cementitious matrix had good bonding with the aggregate, and there existed fly ash particles with different degrees of reaction. The Ca/Si value of AAFSC was smaller than that of cement concrete.

In order to efficiently utilize industrial solid waste while minimizing the preparation cost of engineering materials and the technical difficulty of construction, this paper prepared a high fly ash content alkali-activated fly ash slag composite system at normal temperatures and conducted an in-depth investigation on it. A systematic study was conducted on the workability, mechanical properties, and microstructures of the alkali-activated fly ash slag pastes, including setting times, strength, phase, and molecular structures. We then designed and prepared fiber-reinforced alkali-activated fly ash slag mortar and studied the effects of the alkali activator modulus, glass fiber (GF), and polypropylene fiber (PPF) on the workability, mechanical properties, and frost resistance of the mortar. The following main conclusions were drawn: By adjusting the modulus of alkali activator for alkali-activated fly ash slag pastes, characteristics that meet engineering requirements could be obtained. The compressive strength of the pastes decreased with increasing proportions of fly ash, and it first increased and then decreased with increases in the activator modulus. The flexural strength decreased to varying degrees as the modulus of the activator increased. Through SEM, fly ash particles with different reaction degrees could be observed, indicating that the reaction was still ongoing. The addition of GF and PPF reduced the fluidity of mortar and significantly improved its strength and frost resistance. Fiber had the most significant effect on improving the strength of the mortar, as an activator modulus of 1.0. 0.45% PPF increased the flexural and compressive strength of the mortar by 14.33% and 29.1%, respectively, while 0.90% GF increased the flexural and compressive strength of the mortar by 3.12% and 19.21%, respectively. The frost resistance of the mortar with an activator modulus of 1.0 was significantly better than that of the mortar with an activator modulus of 1.4. 0.45% PPF and reduced the quality loss rate of the mortar by 49.30%, effectively delaying the deterioration of its freeze-thaw performance.