Effect of Strengthening Mechanism of Alkali Curing on Mechanical Properties of Fly Ash Lightweight Aggregates and Its Concrete

The low hydration degree of fly ash in Fly Ash Unburned Lightweight Aggregate (FULA) is not conducive to the development of the mechanical properties of lightweight aggregates and their concrete. In this paper, FULA was immersed in an alkaline solution with the purpose of improving the mechanical properties of FULA and its concrete. Firstly, FULA was prepared using fly ash as the main raw material. The effect of the alkaline solution type and concentration on the basic properties of FULA was studied. Then, lightweight aggregate concrete was prepared using FULA as a coarse aggregate. The role of the aggregate category and water-cement ratio in the mechanical properties of concrete was analyzed. Finally, the effect of alkali curing on the interfacial transition zone of concrete was tested by combining an electron microscope and microhardness tester. Based on this, the strengthening mechanism of alkali curing on the mechanical properties of concrete was proposed. The results show that alkali curing can effectively improve the mechanical properties of FULA and its concrete. The microhardness of the interfacial transition zone of alkali curing FULA concrete is significantly higher than that of the cementite matrix, and the closer the aggregate, the higher the microhardness. The fundamental reason for this is that alkali curing improves the hydration degree of fly ash.