Experimental Research On Bond Performance Between Steel Bar And Slag-fly Ash Based Geopolymer Concrete

Through the experimental study on the basic mechanical properties of slag-fly ash based geopolymer concrete and the bonding and anchorage properties of steel bar and Geopolymer Concrete(GPC,Geopolymer Concrete)at the condition of room temperature curing,the following main results are obtained:(1)Basic mechanical properties of slag-fly ash based GPC with thress different compressive strength grade were tested,including compressive strength,elastic modulus,splitting tensile strength and compressive stress-strain relationship.The results show that the elastic modulus of GPC is equivalent to that of PCC.The splitting tensile strength of GPC is much higher than that calculated results by the existing formulas.(2)The bond property between steel bar and GPC was studied through 11 groups of pull out tests.The influence of various factors on bond strength was studied,and the difference of bond performance between GPC and PCC was compared.The failure modes and bond stress-slip curves of the specimens were analyzed.The results show that the bond strength between GPC and steel bar is significantly higher than that between PCC.Bond length,concrete strength and steel bar diameter have significant effects on the bond failure mode.The bond strength between steel bar and GPC increases with the increase of concrete compressive strength and decreases with the increase of bond length.The diameter of steel bar has no obvious effect on bond strength.The bond strength between round steel bar and GPC is only 26.9% of that of ribbed steel bar.The experimental values of bond strength between ribbed steel bars and GPC are higher than those predicted by Orangun and Esfahani formulas,and close to those predicted by Dahou and Al-Azzawi formulas.(3)According to ACI 318-19 and ACI 408-R03,the bond properties between bar and GPC in reinforced GPC beams were studied.20 specimens of reinforced concrete beans,including 2 PCC beams and 18 GPC beams,were tested.The effects of compressive strength,bar diameter,lap length,cover thickness and stirrup constraints on bond performance of lap beans were studied,and the prediction results of development length in ACI 318-14 and ACI 408-R03 were compared.The results show that the ultimate stress of longitudinal tensile bars in the lap section of GPC beam is higher than that of PPC beams,and the bond performance between bars and GPC is stronger.Increasing the compressive strength of concrete,relative cover thickness and stirrup constraints can improve the bond performance between bars and GPC,and increasing the lap length can increase the ultimate stress of the longitudinal tensile bars.Compared with the test results,ACI 318-14 and ACI 408-R03 formulas are relatively conservative in predicting the ultimate stress of the tensile bars of GPC beam,and ACI408-R03 formula is closer to the test results.Based on ACI 408-R03 formula,the strength influence coefficient is modified,and the new development length prediction formula is put forward.The calculation results of ultimate stress of tensile bars are in good agreement with the test results and the existing test results.