Effect of dry–wet ratio on pore-structure characteristics of fly ash concrete under sulfate attack

Abstract

At present, a unified sulfate dry–wet cycle system has not been found, different researchers use various dry–wet cycle methods, and the research results are often difficult to systematize. In this study, dry–wet time ratios of 1:1, 3:1, 5:1, and 7:1 were employed to investigate the effect of sulfate drying–wetting cycles on the pore-structure characteristics of concrete. The wetting and drying temperatures were set to 25 and 60 °C, respectively, and the concrete specimens were subjected to drying–wetting cycles for 150 days. The evolution of the concrete property was characterized based on the flexural strength. Moreover, the mineralogical composition was analyzed through X-ray diffraction, and the sulfate content was measured through spectrophotometry. Mercury intrusion porosimetry was applied to determine the pore-structure parameters of concrete, and the microstructure of eroded concrete was analyzed through scanning electron microscopy. The results showed that the pore volume of concrete under sulfate attack decreased significantly, and the reduction in intrusion was mainly observed in pores of 50–200 nm. The generation and propagation of micro-pores and micro-cracks have an important impact on the deterioration of concrete performance.