Corrosion Mechanism And Mechanical Properties Of GFRP Rebar In Alkaline Solution

Steel corrosion is one of the main problems of concrete structure durability.Compared with the steel,GFRP rebar has the advantages of high strength,low density and good corrosion resistance to acid.Therefore,GFRP becomes a good choice to replace steel bar in concrete structure.Since GFRP material is susceptible to the alkaline conditions,it is necessary to clarify the mechanical properties and corrosion mechanism of GFRP rebar in such an alkaline environment of interior concrete.In this study,two tests of GFRP rebar(epoxy and unsaturated polyester resin matrix)were carried out: One was corrosion and tensile test of GFRP rebars in the artificial alkaline solution,the other one was corrosion and tensile test of GFRP Specimens.The testing results showed that after the 90 days’ test,there were many pits on the surface of GFRP rebars,glass fiber and resin matrix were seperated,the PH value of the alkaline solution decreased from 13.62 to around 12.85,indicating that the hydroxyl ions of the alkaline solution had reacted with GFRP rebar.The mass of GFRP rebar had rarely changed,the residual percent(RP)of mass are both above 97%,but the tensile strength of the two kinds GFRP rebars reduced about 30% after 90-day immersion test in alkaline solution at 60 ℃,the RP of epoxy resin GFRP rebar was higher than the one of UPR(unsaturated polyester resin matrix GFRP rebar),which indicated epoxy resin GFRP rebar had better alkali-resistance.The corrosion and tensile test of GFRP Specimens as a comparison was in the same conditions of the corrosion and tensile test of GFRP rebars in the artificial alkaline solution.After 30 days,60 days,90 days,the tensile strength retention of GFRP rebars in C40 concrete was higher than in the artificial alkaline solution.When the environment temperature was 60 ℃,after 90 days,tensile strength retention rate of GFRP rebars in C40 concrete dropped to 81.56%,tensile strength retention rate of GFRP rebars in saturated calcium hydroxide solution of dropped to 73.6%.In addition,the relationship between the loss of tensile strength and the reduction of PH can be determined.That means the durability of GFRP rebar in concrete can be enhanced by controlling or limiting the alkalinity when producing concrete.In the end of this paper,the data of Arrhenius predicting model were used to compare with the testing data.The predicted results and the experimental results have little difference for the UPR GFRP rebar,but for epoxy resin matrix GFRP rebar,the experimental results and the predicted results have great difference.