Behavior of fiber reinforced cementitious composites under the coupled attack of sulfate and dry/wet in a tidal environment

Abstract

As an essential building material for marine engineering structures, concrete is exposed to both sulphate and wet and dry cycles in a tidal environment, which can easily affect the reliability and service life of marine structures. This study investigates the performance of polyvinyl alcohol (PVA) fiber reinforced cementitious composites subjected to combined action of sulphate and wet/dry in a tidal environment. Nine mixtures with the incorporation of fly ash and bentonite were used and the specimens were exposed to Na2SO4(aq), water and MgSO4(aq) for 150 wet and dry cycles. The physical and mechanical properties were studied for degradation, including mass change, relative dynamic modulus of elasticity and change in compressive strength. In addition, acoustic emission techniques were used to provide real-time monitoring of the damage process of the samples during compression. Meanwhile, nuclear magnetic resonance technology was used to observe the pore distribution under different deterioration ages. The results showed that the durability properties decreased with the raise of fly ash and bentonite in Na2SO4(aq). In contrast, the highest durability of the samples was achieved at a ratio of 1.8:1 of fly ash to cement in water. As the fly ash and bentonite content raised, the activity of the acoustic emission signal decreased continuously. and the acoustic emission signal gradually changed from multiple peaks to single peaks. With the progress of wet and dry cycle, the small pores were gradually connected to form large pores, and the increased fly ash and bentonite amounts decreased the number of small pores. After 150 wet and dry cycles, the durability behaviour of fiber reinforced cementitious composites in different kinds of solutions were: water > MgSO4(aq) > Na2SO4(aq). This research serves as a theoretical basis for the development of PVA fiber reinforced cementitious composites used in marine structures which are subject to sulphate deterioration and wet-dry cycles.