Analysis Of Interface Shear Behavior Between Magnesium Phosphate Concrete And Normal Concrete

Magnesium Phosphate Cement(MPC)is a kind of cement material with advantages such as fast setting and hardening,wear resistance and frost resistance.Extraodinary performance of MPC enable it have a broad application prospect in the field of bridge concrete structure repairment.The interface between old and new concrete is too often the weakest position of the concrete restoration structure.Under the action of external load,the interface shear performance places a very important influence on the concrete reinforcement engineering.On purpose of solving the problems mentioned above,this thesis firstly examined the mechanical properties of MPC Concrete,and then conducted direct shear tests of MPC concrete-normal concrete(NC)with various interface treatment methods in order to study the influence of different interface methods on the shear properties of MPC concrete-NC interface.The primary research contents and conclusions of this paper are as follows:(1)Study the influence of the type and amount of admixtures on the compressive strength of MPC concrete,and compare the difference of mechanical properties between MPC concrete and NC concrete.It is found that there is an optimal water-binder ratio and water-reducing agent content,borax and large particle size aggregate can reduce the compressive strength of MPC concrete.The compressive strength of MPC concrete at 1d,3d and 7d can reach 46.7%,66.3%and 81.9% of the compressive strength of 28 d,while that of NC concrete at the same time,only36.4%,42.4% and 60.9%.(2)MPC concrete-NC direct shear test is conducted to study the influence of interface treatment on the shear bond strength and failure form of MPC concrete.The maximum shear strength of Cutting-Slot(CS),Bar-Planting(BP),Grooving(Gro)and Roughing(Rou)interfaces were 6.029 MPa,5.545 MPa,2.490 MPa and 2.435 MPa,respectively.The failure mode of the Rou specimen and the CS specimen is brittle failure of the bonding surface.The end of the elastic section of the Gro specimen suddenly enters the plastic development stage after failure.The elastic stage of the BP specimen is smoothly connected with the plastic deformation stage,and there is no brittle failure in the whole loading process.(3)MPC concrete has good shear bond strength with NC.Comparing the shear strength of specimens in this paper with that of other types of concrete,the maximum shear strength of Rou,CS,Gro and BP interface are greater than 71.43%,100%,23.07% and 89.74%,respectively.(4)The interface parameters of MPC concrete-NC direct shear specimens were analyzed,and the influence of surface parameters on shear strength was studied.The shear strength of CS interface is related to the width and depth of CS interface.The shear strength of the Gro interface firstly increases and then decreases with the increase of Gro depth.The shear strength of the BP specimen is related to the diameter and embedment depth of the reinforcement.The shear strength increases with the increase of the diameter of the reinforcement and the embedment depth of the reinforcement.(5)Interface treatment affects the evolution law of load-slip curve of direct shear specimens,and the characteristics of each stage of curve evolution correspond to the failure modes of specimens at different stages.Based on the measured evolution law of load-slip curve,a simplified load-slip model is proposed.There are only elastic sections in the load-slip curves of the Rou interface and the CS interface.At the end of the elastic section of the load-slip curve of the Gro interface,the plastic phase suddenly enters,and the shear strength fails when the interface cracks through.After the end of the elastic section at the interface of the BP reinforcement,the shear stress continued to rise with the increase of slip amount,and began to decline after reaching the maximum value.The shear stress remained around a certain value,and the slip continued to increase until the specimen was damaged.(6)Abaqus was used to establish the finite element model of the direct shear specimen with BP interface,and the influence of the internal stress distribution of the direct shear specimen was studied.The results show that the reinforcement has a great influence on the internal stress distribution of the specimen.The load-slip curve calculated by finite element is in good agreement with the load-slip curve obtained by the test data,which verifies the feasibility of Abaqus finite element simulation of direct shear specimen.