Assessing the effects of Na2SO4 and NaCl on the properties of geopolymer concrete subjected to elevated temperatures

Since concrete is exposed to chemical, mechanical, or physical deteriorating effects simultaneously or successively under environmental conditions, this study focused on the durability of geopolymer concretes containing ground blast furnace slag (GGBFS) and fly ash (FA) under the effects of sulfate and salt after elevated temperatures. For this aim, five FA-based geopolymer concrete mixtures with different GGBFS contents were produced and cured at 90degree celsius for 72 h. First, the produced samples were exposed to 200, 400, 600, and 800degree celsius for 2 h. Then, the samples were put into 5% sodium sulfate (Na2SO4) and 5% sodium chloride (NaCl) solutions for 30 days. The impacts of elevated temperature + Na2SO4 and elevated temperature + NaCl on geopolymer concrete were investigated by compressive strength, mass loss, visual examination, capillary water absorption, x-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR). As a result, although cracking or strength decreases in concrete have been observed after only elevated temperatures, it has exhibited significant resistance to the integrated deterioration influences, has not disintegrated, and maintained its integrity under appropriate mix design and curing conditions. Shortly, the results demonstrated the ability of geopolymer concrete subjected to elevated temperatures with acceptable strength and durability under chemical effects, even if left for a short time.