Experimental Study On The Alkali Resistance Of BFRP For Concrete Reinforcement In Hygrothermal Environment

Marine environment is one of the harshest corrosive environments in the wild, thus, marine structures are subjected to seawater, marine atmosphere or even more severe corrosion such as splash zone and tidal zone. Traditional steel materials are susceptible to corrosion and their serviceability may be lost within a short service time. Replacing steel bars with FRP bars is considered to be an effective method to thoroughly solve the problem of steel corrosion in concrete. However, there are still some problems lying in the alkali resistance of BFRP and GFRP barsin hygrothermalenvironment.The FRP bars in concrete structures immersed in seawater are exposed to a combined corrosive environment composed of salt solution (seawater) and alkali solution (concrete pore solution) in marine engineering. In that environment, their corrosion resistance degradate. Thus, to research the durability of FRP bars in the practical marine concrete structures, accelerated aging tests in alkali-salt mixed solution at 55 degrees Celsius was adopted in this study to simulate the corrosion of FRP bars subjected to a coupling environment with seawater and concrete pore solution.In this study, polyethylene(PE) was added to D430 vinyl ester resin with three different mass ratios and its volume shrinkage was effectively reduced. Adding polypropylene glycol diglycidyl ether (PPGDGE) with different mass ratios,andusing methyl tetrahydrophthalic anhydride as curing agent and imidazole as accelerant,the toughness of E51 epoxy resin could be significantly enhanced. The tensile properties and moisture rates were compared among different aging durations. It was concluded that the addition of PE powder enhanced the durability of D430 in alkali-salt mixed solution. In contrast, PPGDGE toughening agent lowered the durability of epoxy resin.Tensile properties, moisture rates and shear properties of those five groups of FRP bars with different aging durations were analyzed and compared. The results showed that vinyl ester resin BFRP (BV FRP) bars demonstrated better durability than BE FRP bars with anhydride curing agent. The corrosion resistance of B430 FRP bars could be enhanced by reducing their volume shrinkage.5% Addition of PPGDGE could improve the corrosion resistance of BE FRP bars, while excessive addition decreased their corrosion resistance instead. The corrosion resistance of BFRP bars was independent of rib height but depended on the forming process of rib. The coating on the surface could not enhance corrosion resistanceof BFRP bars since it tended to fail in hygrothermal environment.Comparing the retentions of tensile and shear strength of FRP bars with different aging duration, it was concluded that BFRP bars performed higher shear strength retentions than tensile strength retentions. In terms of the differences between their shear strength retentions and tensile strength retentions, the differences of BV FRP bars were small, while those of BE FRP bars were large.