| The concrete pouring construction process is generally completed in one go to ensure the integrity of the structure.However,when encountering natural disasters such as damage,increased bearing requirements,or degradation of its own strength,the old concrete needs to be reinforced.When new concrete is poured on top of the old concrete,new and old concrete forms.The good bonding performance of the bonding surface between new and old concrete is the key to normal service,and the shear performance of the bonding surface is often used to evaluate the bonding performance.The shear resistance between new and old concrete includes cohesion,friction,and interlocking force.However,there is relatively little research on the relationship between the morphology of the bonding surface and interlocking force,and there is a lack of comparison between the specific force value of interlocking force and other shear resistance values.The importance of interlocking force in shear performance is relatively unclear.Therefore,this article designs oblique shear specimens of new and old concrete with different bonding surface morphologies The main research content on the relationship between shear strength and interlocking force is as follows:(1)A study was conducted on the failure pressure of oblique shear concrete with the same average roughness and different morphology of the bonding surface.It was found that the average roughness cannot accurately describe the level of bonding surface treatment,and the bonding surface morphology is closely related to the interlocking force.Even if the average roughness is the same,the interlocking mechanism of the new and old concrete bonding surfaces is not the same,and there are two types of interlocking:cement mortar interlocking and aggregate interlocking,Moreover,the maximum shear failure strength in the interlocking state of aggregates is 3.46MPa higher than that in the interlocking state of cement mortar.In addition,the bonding state of chiseled specimens is more unstable,and the data dispersion is higher than that of groove specimens.(2)The pure shear strength of the bonding surface between new and old concrete is studied when the average roughness is the same and the groove size is different,and the strength envelope of the new and old concrete is obtained.The results show that interlocking force is the main influencing factor on the shear strength of new and old concrete.The cohesion of the bonding surface of new and old concrete is 2.28 MPa,the interlocking force provided by cement mortar interlocking is 0.81 MPa,which is 35.65%of the cohesion,and the interlocking force provided by aggregate interlocking is 2.05 MPa,which is 90.02%of the cohesion;The common formulas for calculating the shear strength of new and old concrete do not fully consider the interlocking state,resulting in deviations between the calculated values and the experimental values.The calculated values obtained from the groove type formula are higher than the experimental values,while the calculated values obtained from the chiseling type formula are lower than the experimental values.(3)We studied the oblique shear failure characteristics of new and old concrete with the same average roughness and different groove sizes.The results show that when the groove size is smaller than the minimum aggregate particle size,there are many voids on the bonding surface of the groove failure,and there are few occurrences of aggregate being cut in the groove;When the width of the groove is 400%of the minimum aggregate particle size,the diagonal shear compressive strength increases by 45.34%compared to the cast state treated specimen,and when the groove depth is the same as the minimum aggregate particle size,the diagonal shear compressive strength increases by 41.22%compared to the cast state treated specimen;There is a correlation between the size of the groove and the combined stress between the grooves,which affects the shear performance of the new and old concrete;The ductility of new and old concrete specimens with interlocking aggregates has been improved;The interlocking mechanism can significantly affect the loss of total energy,elastic strain energy and dissipated strain energy of new and old concrete during oblique shear,and the shear resistance of new and old concrete is more closely related to the energy change in the plastic section than the elastic section. |
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