Setting time and mechanical properties of chemical admixtures modified FA/GGBS-based engineered geopolymer composites
Yi Zhang, Wenhua Liu, Minghui Liu
Abstract
Eleven common chemical admixtures , including sodium lignosulfonate , borax , citric acid , sucrose, sodium gluconate, sodium pyrophosphate, sodium hexametaphosphate, sodium tripolyphosphate, calcium sulfate, anhydrous sodium sulfate, and anhydrous calcium chloride , were investigated at a 3 wt% addition rate to assess their impact on the fundamental properties of FA and GGBS-based engineered geopolymer composites (FA/GGBS-EGC). These properties encompass setting time, flowability , compressive strength , and tensile properties . The objective of this phase is to identify chemical admixtures with optimal retarding effects on FA/GGBS-EGC. Upon a comprehensive analysis of the test results, borax and sodium gluconate were identified as effective retarders for controlling the setting time of FA/GGBS-EGC while demonstrating beneficial or no adverse effects on other properties. Sucrose, sodium tripolyphosphate, and sodium sulfate also exhibited retarding effects on the setting time of FA/GGBS-EGC. However, their use weakened some mechanical properties of the composites, designating them as potential retarders . Sodium lignosulfonate functioned as a water-reducing agent, while citric acid , sodium hexapentapeptide, calcium sulfate, and anhydrous calcium chloride reduced the setting time of FA/GGBS-ECC. Subsequently, borax, identified as the most effective retarder. The effect of borax addition rate on the basic properties of FA/GGBS-EGC was further investigated at 3%, 4%, 5%, 6% and 8%. Moreover, various characterization tests, including reaction kinetics, XRD , DTG, XPS, and pore solution chemistry, were conducted on FA/GGBS-EGC. The retardation mechanism of borax is discussed based on the results of these tests. In addition, the addition of 8 wt% borax extended the setting time of FA/GGBS-EGC to four times that of the control group, with 5 wt% borax yielding the best mechanical properties.