Study On The Interface Bonding Performance Between Fast-hardening ECC And Existing Structures

Ordinary concrete is brittle,and it is easy to crack during the force process after being prepared into a component,resulting in insufficient durability.A fast-repair material with high ductility is needed to solve this problem.Magnesium phosphate cement is a cement-based material with fast setting hardening,high early strength and good bonding strength.It is widely used in concrete structures and road repair and other fields.In this paper,magnesium phosphate cement and PVA fiber were used to prepare a fast cementitious composite with a limit tensile strain stability of more than 3%（ECC）.The mechanical properties of fast-hard ECC were analyzed by basic tests and other methods;The interface bonding performance of fast hard ECC and existing structures was analyzed by acoustic emission and digital image correlation,and the specific research contents and results are as follows:（1）The study on the strength of fast-hard ECC mainly analyzes the compressive strength,flexural strength and tensile strength at the age of 1h,2h,3h,4h,5h,6h,1d,3d,7d and 28d.The results show that at 6h,the compressive strength reaches 25.63MPa,the flexural strength reaches 13.96MPa,and the tensile strength reaches 3.41MPa.At 28d,the compressive strength reaches 50.45MPa,the flexural strength reaches 20.95MPa,and the tensile strength reaches 5.03MPa.It can be seen that the compressive strength,flexural strength and tensile strength at 6h have exceeded 50%at 28d,indicating that the fast-hard ECC has the characteristics of rapid growth in early strength.（2）Regarding the research on fast-hard ECC hydration products,the hydration heat release and product generation were mainly analyzed.In the hydration reaction of fast-hard ECC,the main hydration products dominated by Mg KPO₄·6H₂O crystals were generated.The reaction process was mainly concentrated in the early stage,and the accumulation of hydration exothermic heat within 1d quickly reached 173J/g,accounting for 92%of the 3d exothermic heat.With the change of age,the ratio between the components of the hydration product also changes.The weight loss interval of hydrated products is concentrated between 50°C～200°C.（3）Regarding the research on bonding strength,the flexural strength development law,load-displacement,internal stress state and surface strain of fast-hard ECC flexural bonding,oblique shear bonding,composite bonding in repair compression zone and composite bonding in repair tensile zone were analyzed.The results show that the flexural bond strength reaches 2.29MPa at 6h and 4.13MPa at 28d.The diagonal shear bonding strength reaches 5.89MPa at 6h and 14.23MPa at 28d.The flexural strength of the composite bond of ECC in the compression zone reaches 6.53MPa at 6h and9.43MPa at 28d.The composite flexural bonding strength of ECC in the tensile zone reaches 12.39MPa at 6h and 17.67MPa at 28d.A large number of acoustic emission signal points will be generated during the loading process,and the failure pattern is affected by the bonding interface and loading rate.The final failure stage has high amplitude,peak frequency and energy,and the eigenvalue B value is small.In addition,a bond strength calculation model was established.