Research On In-situ Strength Inspection Methods Of Cementitious Grout For Coupler Of Rebar Splicing

There are indispensable joints and seams in precast concrete structures.The reliable connection between joints and seams is an important guarantee for precast concrete structures to meet the design requirements of "equivalent cast-in-place".Rebar sleeve connection with injected grout is one of the main forms of vertical member connection in precast concrete structures,The grouting material in the sleeve is the main medium for load transfer of different components,and its quality determines the carrying capacity and seismic performance of the whole building.As an important index to evaluate the quality of grouting material,in-situ compressive strength is the key factor to ensure the joint performance of sleeve grouting.However,in practical engineering,due to improper operation of construction personnel,arbitrary increase of water consumption and use of inferior grouting material and other phenomena,the actual strength of grouting materials can not meet the design requirements from time to time,which seriously affects the safety of the building structure.Therefore,it is very important to study the detection method of the in-situ compressive strength of grouting material.In this paper,the influence of compressive strength of grouting material on the mechanical properties of sleeve connection with injected grout is analyzed.Then,the paper studies the detection method of the in-situ compressive strength of the sleeve grouting material,creatively proposes to use the surface hardness method to detect the in-situ compressive strength of the grouting material,establishes the corresponding strength curve,and verifies the detection ability of the surface hardness method.At the same time,this paper also studies the small core sample method to detect the compressive strength of the grouting material,and determines the conversion coefficient of the compressive strength between the core sample of the grouting material and the standard sample.The main research results and corresponding research results are as follows:(1)Effect of compressive strength of grouting material on mechanical properties of sleeve connection with injected groutThree different types of grouting sleeves are selected to make different strength grade of joint specimens for medium uniaxial tensile test.The results show that under the condition that the grouting is full and the anchorage length of the steel bar is set as 8d(d is the diameter of the connecting steel bar),the larger the sleeve size is,the higher the compressive strength of the grouting material is required in order to make the tensile strength and yield strength of the joint specimen meet the standard requirements.(2)Detection the compressive strength of sleeve grouting material by surface hardness methodBased on the characteristics of the sleeve grouting material and the structure of the sleeve connection with injected grout,the instrument of the surface hardness method is determined.The relationship between the surface hardness and compressive strength of sleeve grouting material was studied,the relationship curves between the surface hardness value and the compressive strength value of the grouting material standard specimens and the relationship curves between the surface hardness value of the grouting material simulated specimen and the compressive strength value of the corresponding standard specimens were established respectively.The results show that there is a strong correlation between the surface hardness and compressive strength of grouting material.The best regression fitting effect is obtained by using the exponential function.The average relative error and relative standard deviation of the two intensity curves are within 15%,which is in line with the accuracy requirements of the intensity curve.When the compressive strength is the same,the surface hardness of the simulated specimen is obviously greater than that of the standard specimen.Therefore,when detection the in-situ compressive strength of the sleeve grouting material,it should be based on the strength curve inferred from the simulated specimens(3)Verification of surface hardness detection capabilityThe two strength curves were verified in the laboratory,and the strength curves of the simulated specimen were applied to the practical engineering to evaluate the detection effect of the surface hardness method.The laboratory test results show that: the strength curve of the simulated specimens can be applied to different brands of grouting materials;the strength curve of the standard specimens can be applied to the specimens after curing to 14 days.The practical engineering verification results show that the relative error range of test results is 7.8%?11.5%,all less than 15%,which can meet the requirements of engineering test.(4)Detection the compressive strength of sleeve grouting material by small core sample methodFive different brands of grouting materials were used to make core samples and standard samples.The conversion coefficient of compressive strength between core samples and standard samples was determined through the test.The test results show that the compressive strength of the core samples is linearly related to that of the standard samples,and the compressive strength of the standard samples is about 1.12 times of that of the core samples.