Experimental Study On Compression Shear Composite Mechanical Properties Of Cement-based Grouting Materials After High Temperature

CGM-270 cement-based grouting material used in this paper is a mixture of cement,fine aggregate,doushi granule and some additives,Its advantage is that it will have greater fluidity after adding appropriate water,and can obtain high strength in a short time,Because of its excellent characteristics,it is often used in secondary grouting of equipment foundation,reinforcement and repair of concrete components and other fields.In the concrete structure engineering,the state of composite stress is often more,and because of the modern society,the occurrence of fire has not been well restrained,it is very important to study the strength criterion of cement-based grout under composite stress state after high temperature.The main research work and conclusions are as follows:(1)The basic mechanical properties and high temperature tests were carried out on 24 standard cube blocks with side length of 100 mm and 12 prismatic blocks with100 mm × 100 mm × 300 mm,respectively.The results show that the color of the cube surface experiences the change process of gray-pale-white weight-red brick color.And with the gradual increase of temperature,the cube compressive strength decreases slowly,and the axial compressive strength and splitting tensile strength of cement-based grout have the same trend.The burning loss rate of the cube test block of grouting material is higher in the range of 200 ℃ ～ 400 ℃.(2)Based on the analysis of compression shear specimens at home and abroad,Z-shaped specimens are used for direct shear and compression shear tests.The self-made wood formwork was used for pouring,the direct shear test results were sorted out,and the direct shear stress-strain curves after different temperatures were drawn.Analysis of the law of change,It can be found that with the increase of temperature,the direct shear strain of cement-based grouting material increases,and the shear stress is getting smaller and smaller.Then the equation of direct shear strength and temperature is fitted by the data.(3)By placing a self-made reaction frame device on the long axis testing machine,it can be used for the compression shear force test and research,Then through the analysis of the compression shear test results at 20 ℃,200 ℃,400 ℃ and600 ℃,it is found that the ultimate shear stress and ultimate shear strain increase with the increase of axial compression ratio.The shear stress-strain constitutive model of grouting materials under different working conditions is established by boltzann formula.(4)The compression shear strength was studied.The results show that with the increase of temperature,the compressive shear strength of cement-based grouting material decreases gradually.A three-parameter strength criterion of double shear stress is proposed for cement-based grouting materials at different temperatures.Combined with the data,the formula of compressive shear strength of grouting material after high temperature is deduced.On the basis of the criterion,the shear bearing capacity formula of concrete columns strengthened by replacement is deduced,which lays a foundation for the future grouting reinforcement.The reduction degree of shear strength of grouted frame column under high temperature of 600 ℃ is obtained through calculation of an example.