Strength Enhancement Mechanism of Slaked Lime on One-Part AAM Prepared from Sodium Carbonate–Activated Slag

Abstract

Slaked lime was used to synergize with sodium carbonate to activate the slag. Experimental studies were carried out to investigate the effect of the proportion of activator on its workability and mechanical properties. The hydration products, microstructure changes, and strength enhancement mechanism were also explored by isothermal conduction calorimetry (ICC), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscope (SEM) tests. The results show that with the increase of slaked lime doping, the compressive strength increases and then decreases, the fluidity gradually decreases, and the setting time decreases and then increases. The maximum 7- and 28-day compressive strengths were 24.1 and 30.2 MPa at 6% slaked lime dosage, which were 4.8 times higher than those at 0% dosage. This is mainly due to the fact that the reaction products of slaked lime and sodium carbonate can promote the alkali activation reaction, in addition to the fact that higher Ca2+ in the system is favorable to promote C─ (A)─ S─ H generation. However, when the dosage of slaked lime is greater than 8%, the hydrated gel in the system decreases and precipitates more square flakes of Ca(OH)2, which reduces the interlayer bonding of the hydrated gel, thus reducing the strength. The slaked lime admixture can effectively promote the internal Si and Al dissolution and condensation of slag, improve the rate of hydration reaction, and promote the generation of hydration gel C─ (A)─ S─ H, so that the alkali-activated slag matrix is denser and the strength is improved.