Development of a Novel Type of Liquid Accelerator Based on Aluminum Sulfate and Its Accelerating Mechanism for Cement Hydration

Abstract

A novel chlorine- and fluorine-free liquid accelerator was developed in this study. The proportion of each component of the accelerator was determined using an orthogonal test method. Various additives’ impact on the cement setting time and concrete compressive strength was analyzed. The mechanism of the accelerator on cement hydration was examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) experiments. The results showed that the optimal ratios for the raw materials were 45% aluminum sulfate, 15% sodium metaaluminate, 5% magnesium sulfate, 3% citric acid, 7% triethanolamine (TEA), and 1% polyacrylamide to make the liquid accelerator. At a concentration of 5% accelerator, the initial setting time of cement was 210 s and the final setting time was 380 s. The compressive strength of the concrete test block was 11.4 MPa after 1 day and it increased to 28.32 MPa after 28 days. This represents a 141.6% increase in compressive strength after 28 days. The addition of the accelerator consumes Ca2+ and promotes the formation of ettringite (AFt) and gypsum (Gyp), thus promoting cement hydration, reducing initial setting time, and densifying cement’s internal structure. The accelerator not only has low production cost and excellent quick-setting effect, but also can improve the strength of concrete, making it suitable for a wide range of applications.