Experimental Study On The Mechanical Properties Of Hybrid Fiber Reinforced Cementitious Composites And Its Bonding Properties With Concrete

Hybrid Fiber Reinforced Cementious Composites(HFRCC)have good performances in tension,bending,shear,crack resistance,shrink resistance,impermeability,corrosion resistance,abrasion resistance and impact fatigue resistance.Compared with cement-based materials reinforced by single type fibers,HFRCC can improve the uniformity of fibers in spatial distribution.The hybrid fibres with high and low elastic modulus can achieve a "positive hybrid effect" on HFRCC mechanical properties at different scale levels and loading stages,which will improve the fiber efficiency and reduce cost of materials.With these characteristics,HFRCC can be used as repair materials to improve the bearing capacity and durability of damaged concrete structures,consequently,it has a broad application prospect.If HFRCC are used as repair materials for concrete structures,the interface bonding hehavior is essential to the quality of repair system.Therefore,relevant experimental studies on the mechanical properties of HFRCC and the interface bonding behaviour between HFRCC and concrete were conducted.The main conclusions are as follows:(1)The flexural and compressive tests of 12 groups of 40 mm×40 mm×160 mm prismatic specimens were carried out.The effects of PVA/steel fiber volume fraction,fly ash dosage and water-binder ratio on compressive strength and bending strength were analyzed.The results show that with the increase of water-binder ratio and fly ash dosage,the compressive strength and bending strength of HFRCC are decreased.The PVA fiber can significantly increase the bending strength of HFRCC,while reduce the compressive strength of HFRCC.At a certain range of fibre volume fraction,steel fiber can improve the bending strength and compressive strength of HFRCC.When the steel fiber volume fraction is 0.15%,both of the flexural strength and compressive strength reach to the maximum,which are 23.6 MPa and 59.2 MPa respectively.(2)The four-point bending test of 12 groups of 15 mm×100 mm×400 mm plate specimens were carried out.The effects of PVA/steel fiber volume fraction,fly ash dosage and water-binder ratio on flexural properties of HFRCC were analyzed.The results show that When PVA fiber and steel fiber are mixed,the flexural performance can be significantly improved by increasing the PVA fiber volume fraction.At a certain range of fibre volume fraction,steel fiber can improve the ultimate bending strength and bending toughness of HFRCC.However,excessive steel fiber will inhibit the development of multiple cracking.When water-binder ratio is 0.35 and fly ash dosage is 55%,the bending performance of HFRCC reaches the optimum.(3)The splitting tensile test of 10 groups of 100 mm×100 mm×100 mm cube bonding specimens were carried out.The effects of PVA fiber/steel fiber volume fraction and HFRCC matrix strength on the bond splitting tensile strength between HFRCC and concrete were analyzed.The results show that when PVA fiber and steel fiber are mixed,the increase of PVA fiber/steel fiber volume fraction can improve the bond splitting tensile strength between HFRCC and concrete to a certain extent,and the increase of HFRCC matrix strength is also helpful to improve the bond splitting tensile strength.(4)The shear test of 10 groups of 100 mm×100 mm×100 mm cube bonding specimens were carried out.The effects of PVA fiber/steel fiber volume fraction and HFRCC matrix strength on the bond strength between HFRCC and concrete were analyzed.The results show that when PVA fiber and steel fiber are mixed,the increase of PVA fiber volume fraction can improve the bond shear strength to a certain extent.However,the bond shear strength decreases first and then increases with the increase of steel fiber volume fraction,and when steel fiber volume fraction is 0.75%,the bond shear strength reaches the maximum value of 2.39 MPa.The increase of HFRCC matrix strength is helpful to improve the bond shear strength between HFRCC and concrete.(5)The multi-factor prediction equations of bond splitting tensile strength and bond shear strength were proposed.Based on the bond-slip curves obtained from shear tests,the bond-slip constitutive model considering the PVA fiber/steel fiber volume fractions were proposed.(6)The strain distribution at the bonding interface was analyzed by DIC.The strain extends from the loading end to the free end,which presents a "step" distribution feature.The PVA fiber and steel fiber can increase the strain level at the bonding interface.