Research On In-situ Test Method Of Concrete Strength Based On Rotary Cutting Technology

With the construction of large-scale infrastructure in China,concrete materials are widely used in various engineering projects,and its strength quality has attracted much attention.The realization of rapid and accurate in-situ test of concrete strength is conducive to ensure the quality and safety of the project.In recent years,rotary cutting technology has made significant progress in obtaining rock mechanical parameters,but its applicability to heterogeneous materials such as concrete is not clear.Focusing on how to select drill bits to eliminate the influence of size effect and how to characterize the strength characteristics of concrete materials with the help of rotary cutting drilling operation and response parameters,the in-situ strength test method of concrete based on rotary cutting technology is studied by using the methods of virtual simulation,numerical simulation and physical test.The main research results are as follows:(1)Study on the size of coring bit considering the heterogeneity of concreteAssuming that the cutting effect is mainly controlled by the contact between the drill bit and coarse aggregate,considering the heterogeneity of concrete materials,the digital concrete specimens with different particle size gradation are generated by MATLAB software,and the contact line density between the drill bit and coarse aggregate in the concrete contact surface drilled by diamond coring bit is analyzed;The capacity of the simulation sample under a given confidence is determined by using the theory of mathematical statistics.The frequency curve and standard deviation curve of the linear density versus the size of the bit are analyzed.Finally,the size of the bit is determined to be about 100mm.(2)Study on controlling factors of linear cutting failure mode of concrete materialsBased on the theory of elastic-plastic mechanics and damage mechanics,the numerical simulation model of single tool linear cutting of concrete two-phase heterogeneous materials is established.The effects of cutting depth,cutting speed,tool rake angle and coarse aggregate content in concrete on the cutting force in the cutting process of concrete materials are analyzed.It is found that there is a turning point between linear and nonlinear segments with the cutting depth,and the cutting speed has an important effect on the cutting force The cutting power consumption and cutting specific energy have no obvious influence,and the cutting force increases with the content of coarse aggregate.Based on the critical transition size theory of size effect law,the quantitative relationship between critical failure mode and cutting depth of concrete under linear cutting is established.(3)Research on response characteristics of concrete rotary cutting and prediction model of concrete strengthThe nonlinear dynamic numerical model of rotary cutting of concrete material is established,and the relationship between drilling parameters and mechanical response parameters is analyzed.It is concluded that there is a positive linear relationship between WOB and torque and drilling speed under constant rotating speed;Under constant drilling speed,WOB and torque have a nonlinear decreasing relationship with rotation speed;Under the condition of the same material strength,WOB and torque have a positive linear relationship,which is not affected by drilling speed and rotation speed;XCY-2 rotary cutting penetrometer is used to conduct drilling tests on concrete specimens with different strength grades,and the regular relationship between numerical values and drilling parameters and mechanical response parameters in the test is compared and analyzed.With the help of the existing rock mechanical strength calculation model,the compressive strength of concrete is predicted to verify the feasibility of the method of testing concrete strength based on rotary cutting technology.