Behavior of polyvinyl alcohol fiber reinforced geopolymer composites under the coupled attack of sulfate and freeze-thaw in a marine environment

Abstract

As an important construction material in marine structure engineering, concrete is subject to the dual erosion effects of sulfate and freeze-thaw cycles in a high-latitude marine environment, which is easy to induce damage and affect the normal service life of the structure. In this paper, the behavior of polyvinyl alcohol fiber reinforced geopolymer composites under the coupled attack of sulfate and freeze-thaw in a marine environment were macroscopically and microscopically investigated. Nine mixtures modified with different content of fly ash and bentonite were adopted in this investigation, and samples were exposed to Na2SO4(aq), water, and MgSO4(aq) for 150 freeze-thaw cycles. In this study, the durability of polyvinyl alcohol fiber reinforced geopolymer composites was investigated by weight, relative dynamic elastic modulus, and compressive strength. Moreover, the acoustic emission method was used to monitor the damage process during uniaxial compression in real-time. Meanwhile, the microscopic characterization method was used to identify the microscopic morphology and composition of the aged samples to explore the degradation mechanism of the macroscopic performance. Results show that the durability performance of polyvinyl alcohol fiber reinforced geopolymer composites declined with the increase of the fly ash and bentonite addition in Na2SO4(aq), however, polyvinyl alcohol fiber reinforced geopolymer composites had the highest durability performance when the ratio of fly ash to cement was 1.8 in water. The acoustic emission characteristics were closely related to the damage development and stress-strain curve, and the acoustic emission signal can be divided into the initial stage, stable expansion stage, and unstable expansion stage. With the increase of fly ash and bentonite addition, the intensity and density of the acoustic emission signal were reduced, and the signal distribution was relatively uniform. This research provided a theoretical foundation for the application and popularization of polyvinyl alcohol fiber reinforced geopolymer composites in marine concrete structures which suffer from sulfate erosion and freeze-thaw cycles.