Mechanical and durability performance of polyvinyl alcohol fiber hybrid geopolymer-portland cement concrete under freeze–thaw cycles

Cold winter temperatures at high latitudes in coastal regions lead to prolonged exposure of offshore concrete structures to freeze–thaw (F–T) damage, which significantly reduces the mechanical and durability properties of concrete. To improve the durability of concrete under F–T damage, this study investigated the combined effects of fly ash (FA) and bentonite on the frost resistance of polyvinyl alcohol fiber reinforced geopolymer concrete (PFRGC). The study comprehensively analyzed the effect of fly ash and bentonite content on the rate of mass change and compressive strength under various F–T damage conditions. In addition, uniaxial compressive tests were carried out at different stages of F–T damage and the resulting stress–strain curves and compressive properties were analyzed. Correlations between peak stress, peak strain, modulus of elasticity and deterioration time of the concrete were developed. SEM microscopy tests were also used to investigate the evolution of the internal microstructure and the morphological characteristics of the erosion products under freeze–thaw conditions. The results indicated that the change in concrete mass with a growing number of F–T cycles can be divided into two periods: a gentle increase and a faster increase. A continuous increase in the rate of mass increase was observed for the specimens containing fly ash and bentonite, while the compressive strength of these specimens continued to decrease. During F–T damage, the maximum stress decreased slightly and the maximum strain increased gradually as the volume of bentonite and fly ash increased. This study provides a theoretical basis and technical basis for the development of fly ash and bentonite to improve the frost durability of offshore structures.