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Setting time and mechanical properties of chemical admixtures modified FA/GGBS-based engineered geopolymer composites

2024; Elsevier BV; Volume: 431; Linguagem: Inglês

10.1016/j.conbuildmat.2024.136473

1879-0526

Yi Zhang, Wenhua Liu, Minghui Liu,

Innovative concrete reinforcement materials

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.