The influence and mechanism analysis of aluminum sulfate as an environmentally friendly early strength agent on the properties of cement-based materials

Environmentally friendly chemical admixtures are becoming important in the cement industry. The research objective of this paper is to use aluminum sulfate as an early-strengthening agent to achieve the goals of a large increase in early strength and a reduction in CO2 emissions. The experimental design was as follows: The macroscopic properties and microscopic characteristics of aluminum sulfate were experimentally investigated on five different replacement ratios of 0%, 1%, 2%, 3%, and 4% paste specimens of cement at different ages. The results show that (1) AS4 demonstrated a notable enhancement in early strength, while AS2 and AS3 contributed to increased late-stage strength. Over time, the Ultrasonic Pulse Velocity (UPV) of all samples exhibited a steady rise. Additionally, aluminum sulfate was found to reduce the electrical resistivity of the samples. (2) aluminum sulfate increased the rate of exothermic heat release of samples at induction and acceleration phases, advanced the accumulated heat was high in the samples with high aluminum sulfate content, and the accumulated heat was strongly correlated with the compressive strength. FT-IR and XRD results show that aluminum sulfate promoted the formation of AFt while depleting the CH content, and the TGA results show the content of bound water in the samples increased from Day 1 to Day 28, which had a positive effect on the compressive strength. UHR-SEM results show that increasing aluminum sulfate substitution results in the formation of a denser microstructure. (3) for all the various mixtures, AS2 has the lowest CO2 emissions per unit strength.