Study On Bond-slip Mechanism Between The Ceramsite Lightweight Concrete And High-strength Concrete

Ceramsite concrete composite member is a kind of composite member that uses ceramsite concrete in the tension zone and ordinary concrete in the compression zone.It is generally considered that the bending performance of concrete members is determined by the strength of the concrete in the compression zone and the strength of the tensile reinforcement in the tension zone.If ceramsite concrete is used in the tension zone,not only the bending performance of the component is not greatly affected,but also the weight of the component can be effectively reduced to improve the seismic performance and ductility of the structure,and the cost can be reduced.The position that has an important influence on ceramsite concrete composite member is the pouring joint surface of the two kinds of concrete.Based on the mechanic characteristics of pouring joint surface of ceramsite concrete and high-strength concrete,this paper studies the bonding and slipping mechanism of the pouring joint surface from a multi-scale perspective.The research contents include: experimental analysis of the mechanical properties of the pouring joint surface,mesoscopic finite element numerical simulation analysis of composite member based on random aggregate delivery,analysis of the microstructure and bonding-slip mechanism of the pouring joint surface.Through the experimental study of ceramsite concrete composite members,the influence of different factors on bonding performance of the pouring joint surface was analyzed.The test results show that:(1)The pouring joint surface of the shear specimen is a weak position,and the shear specimen is damaged along the pouring joint surface under different conditions.(2)The Pouring interval and the amount of the additional normal force have a very significant effect on the bonding strength of the pouring joint surface.As the pouring interval decreases and the normal force increases,the bonding strength of the pouring joint surface increases.(3)The treatment of the joint surface and the strength matching of the composite concrete have a significant effect on the bonding strength of the pouring joint surface.The effects of treatments from high to low are exposed aggregate treatment,artificial chiseling treatment,fly ash mortar treatment,and natural bristle treatment;as the strength of post-cast concrete increases,the bonding strength of the pouring joint surface increases.(4)The content of steel fiber has no significant effect on the bonding strength of the pouring joint surface.The effect is best when the content is 0.5%.In the mesoscopic finite element numerical simulation study of composite member,the random aggregate model was used to simultaneously deliver the elliptical aggregate and polygonal aggregate,the mesoscopic finite element models of aggregate,mortar,aggregate interface transition zone and pouring joint surface transition zone are established;the mesoscopic failure characteristics and damage mechanism of composite specimens under different conditions are analyzed;the property fitting formula of the pouring joint surface transition zone at different pouring intervals was obtained.The analysis shows that:(1)The failure of different models is shear failure through the pouring joint surface.The damage starts from the pouring joint surface transition zone.All the exposed ceramsite aggregate on the pouring joint surface is cut off,and the exposed ceramsite aggregates play a shearing resistance role.(2)As the pouring interval decreases,the strength of late poured concrete increases,and the cutting depth increases,the bonding strength increases,but when the cutting depth increases to a certain degree,the effect of improving the bonding strength decreases.(3)The simulation results of the numerical model are basically consistent with the test results.Through the micro-test of pouring joint surface,the microstructure of the pouring joint surface under different conditions was observed,and the morphology and hydration product of the pouring joint surface were analyzed.The analysis shows that:(1)The bonding force of two kinds of concrete is mechanical engagement force,van der Waals force and chemical acting force from big to small.(2)Different joint surface treatments have different effects on the microstructure and hydration product form of the pouring joint surface.(3)Increasing the strength of concrete and reducing the pouring interval can improve the morphology and hydration degree of the hydration products of the pouring joint surface.(4)Two kinds of concrete have different bonding-slip mechanism under different factors: the interval changes the degree of hydration of concrete;the concrete strength changes the amount of slurry at the joint surface;the different treatments affect the three kinds of bonding force acting on the bonding surface respectively;the normal force can change the stress state of the joint surface;the steel fiber has little effect on the bonding-slip performance.