Utilization of Low Reactivity Fly Ash for Fabricating Geopolymer Materials

Low reactivity fly ash (LRFA) is obtained from a low temperature combustion furnace, is a low-pozzolanic activity ash, is a hazardous waste, and is undesirable for engineering applications. The aim of this work is to investigate the mixing procedure for fabricating a cement replacement material, i.e., geopolymer by using LRFA blended with the calcined kaolinite clay as a precursor. A mixture of sodium hydroxide and sodium silicate is used as an alkaline solution. The results show that to obtain sufficient strength for engineering applications, the sequence mixing (SM) procedure is required. Using the conventional mixing method, geopolymer has high porosity and low strength. Because the gas bubbles are generated from the reaction between alkaline solution and the impurity in LRFA during the hardening process. By using the SM method, the generated gas bubbles are released before the geopolymer is hardened. As a result, the porosity is reduced, and the strength is significantly increased. The 7-day strength of geopolymer fabricated by the SM method is higher than the minimum requirement of Portland cement. In addition, the SM procedure reduces the setting time of LRFA-geopolymer, which is an advantage for rapid repair applications.