Investigation On The Interfacial Bonding Behavior Between Early-strength Self-compacting Shrinkage Compensating High-performance Concrete And Existing Concrete

ESS-HPC(Early-strength self-compacting shrinkage-compensating high performance concrete)is a new concrete building material developed on the basis of self-compacting concrete and high performance concrete.Its advantages is that it has excellent crack resistance,early strength,fracture energy and ductility.The flexural and tensile strengths are 2～3 times of ordinary concrete.In order to broaden its application scope,the interfacial bond strength was investigated between the ESS-HPC and normal concrete(NC).In this paper,the bond strength of 16 groups,24 groups and 20 groups of the ESS-HPC&NC under splitting,slant and direct shear tests were investigated,respectively.The ESS-HPC compressive strength,curing age,NC surface roughness,and bonding agent types were chosen as main parameters.Combined with experimental results,the shear strength formula and bond slip constitutive relationship were constructed.The main conclusions are as follows:(1)The cubic bonding splitting tensile tests were used to explore the splitting tensile strength of the ESS-HPC&NC.The influence of the ESS-HPC compressive strength,curing age,NC surface roughness and interface agent types on the interface splitting performance were analyzed.The test results found that the tensile strength of the ESS-HPC&NC was higher than that of the CGM&NC specimens.All specimens showed three failure modes: bonding failure of the interface,NC matrix cracking and failure of the NC.The bond splitting tensile strength of the specimens increased with the increase of the ESS-HPC compressive strength,and showed a linear growth trend.As the age of the ESS-HPC increased,the bond splitting strength firstly increased sharply and then became stably.The NC matrix roughness had a significance influence on the bond splitting tensile strength.Within a certain roughness range,the NC surface roughness firstly increased and then showed decrease tendency.The optimum roughness range was 3.2～3.6 mm.The application of interfacial agent cannot effectively improve the interfacial bonding performance,and the bonding strength may even decrease.(2)The slant shear test of the ESS-HPC&NC was used to investigate the influence of ESS-HPC compressive strength,curing age,NC surface roughness,interface agent and NC matrix compressive strength on slant shear bond strength.The test results showed that there were three typical failure modes of the specimen,i.e.pure interface failure,partial interface failure,and complete failure of the NC matrix.Under the same conditions,the failure mode of the CGM&NC interface was complete failure of the grouting material.The ESS-HPC&NC specimens had a higher shear capacity than that of the CGM&NC specimens.The NC surface roughness,curing age,and NC matrix strength had a greater influence on the interface shear resistance.The larger the NC surface roughness,the longer the age,the higher the strength of the NC substrate,the greater the slant shear bond strength of the interface.Simultaneously,they showed excellent ductility.The influence of the NC compressive strength on the slant shear bond strength showed a different tendency.The slant shear bond strength firstly showed an increase tendency and then decrease when the NC compressive strength grade of C45.While the C55 showed a linear tendency.The influence of the interface agent on the bond strength was not significant,the optimum roughness range was 2.2～2.6 mm.(3)The interfacial bonding performance of the ESS-HPC&NC was studied by direct shear test.The main parameters of the ESS-HPC compressive strength,NC surface roughness,curing age,interface agent and planting bar ratio were chosen to analyse.The results showed that six interface shear failure modes: pure interface failure,tenon-and-mortise shear failure of the ESS-HPC,interface and partial NC failure,complete failure of NC matrix,steel pull-out failure and implanted steel removal + partial NC failure.The interfacial shear strength of the ESS-HPC&NC presented a linear upward trend with the increase of the ESS-HPC compressive strength.As the age of the ESS-HPC increased,the interfacial shear strength increased significantly and gradually stabilized.The NC surface roughness degree had a significant influence on the shear performance of the interface.The optimum roughness range was 4.2～4.6 mm.With the increase of the NC surface roughness,the shear strength of the interface showed a secondary increase tendency.The interface agent had no significant effect on the shear strength,and the most excellent interface agent was the interface without any treatment.The shear strength of the direct shear specimens increased with the increase of the planting bars ratio.Compared with the NC surface smooth group,the maximum improvement can be achieved up to 65.71%when the planting bars ratio increased from 0.31% to 1.32%.The improvement of the shear strength of the interface by chiseling was not significantly improved with the increase of the planting bar rate.(4)Combined with the existing research results and test results,a constitutive relationship model can accurately describe the entire process of ESS-HPC&NC bond-slip failure was established.It was divided into four stages: linear elastic stage,elastoplastic slip stage,plastic enhancement stage and residual failure stage.The experimental data showed a good agreement with the proposed constitutive model.(5)Based on the least square method,the data of the ESS-HPC curing age,NC surface roughness and the ESS-HPC compressive strength were fitted and regression analysis.The interfacial bonding strength of the ESS-HPC&NC specimens under slant and direct shear tests was established with considering multi-factor.The relative error between shear capacity of the ESS-HPC&NC and calculation results was less than 2%.The relationship between the direct shear and the slant shear experimental results was established.The slant shear strength was approximately equal to 4.7 times of the direct shear strength by fitting regression analysis of the experimental values.