The effect of different type aggregates on high temperature resistance in fly ash geopolymer mortars produced with silica fume additive

In this study, the effect of aggregate type on high temperature resistance was investigated in geopolymer mortars activated with sodium hydroxide (NaOH) using silica fume and fly ash. Three different aggregates (basalt, limestone, silica sand), 3 different liquid/binder ratios (0.35, 0.40, 0.45) and 3 different sodium/binder ratios (12%, 15%, 18%) were used in sample production. The produced geopolymer mortar samples were placed in standard molds of 40x40x160 mm and cured at 105 ºC for 24 hours. Then, unit weight, water absorption, permeable void ratio, compressive and flexural strength and ultrasound pulse veolcities of the samples were measured. By evaluating the results, the samples with the highest compressive strength were determined among each aggregate type. A new sample is produced for each temperature test with the mixing ratios of the determined samples; It was exposed to 250 oC, 450 oC, 650 oC and 850 oC temperature effects. After the temperature effect, the weight loss, compressive and flexural strength and ultrasound pulse velocity of the samples were measured. The results obtained were compared with the control samples. As a result of the experiments, strength loss was observed in all geopolymer mortars under the effect of high temperature. It was determined that the samples with the best high temperature resistance among the produced samples were the geopolymer mortar samples prepared with basalt aggregate.