Experimental Study On Mechanical Behavior Of Basalt-Steel Hybrid Fiber High Performance Cementitious Composite Exposed To High Temperature

In this study,a hybrid fiber high performance cementitious composite(Hy F/HPCC)was prepared by mixing hook-type steel fiber(SF)and basalt fiber(BF).In order to study the effects of fiber and temperature on the compressive performance,tensile performance,and bonding performance with existing concrete of the Hy F/HPCC,the compressive test,tensile test,and double-sided shear test were carried out.The mechanical properties of specimens with different fiber addition modes(no fiber,the volume percentage of steel fiber is 1%,hybrid 0.5% BF and0.5% SF,hybrid 1% BF and 1% SF)at room temperature and elevated temperature(100℃,200℃,300℃,400℃,and 500℃)were investigated,and the corresponding calculation models were established.The main findings are as follows:(1)The compression test shows that the high temperature will aggravate the compression brittleness of the no fiber specimen,and the addition of fiber can improve the compression brittle failure caused by high temperature.The peak compressive stress,peak compressive strain,and elastic modulus of the compressive specimens with 1 % steel fiber are close to that of the specimens with 1 % basalt fiber hybrid 1 % steel fiber at each temperature.And the elastic modulus of the specimens mixed with 1 % basalt fiber and 1 % steel fiber is higher.At room temperature and 100 °C,the specimen with hybrid 2 % fiber can obtain the best comprehensive compression performance,and the specimen with hybrid 1 % fiber has the best comprehensive compression performance at 200 °C ～ 500 °C.Basalt fiber can replace part of steel fiber to reduce production costs and improve the compressive properties of specimens.(2)The tensile test shows that the strain hardening ability of the specimen is degraded at300℃ and higher temperatures.There are more cracks in the tensile zone of the specimen with1% SF or mixed 1% SF with 1% BF.The strain hardening ability of the specimen at room temperature,the cracking stress and peak tensile stress at the high temperature can be improved by the hybrid fiber,but the deformation ability at the elevated temperature can be reduced.The specimen with hybrid 2% fiber can obtain better comprehensive tensile properties.(3)The double-sided shear test shows that the failure of the bonding specimens is manifested as the material failure of the existing concrete and the debonding failure of the bonding interface.The material failure of the existing concrete is the main one.And the interface debonding failure of the bonding specimens will be aggravated after high temperature.The shear strength of the bonded specimens was significantly improved after adding fibers,and the effect was better when the steel fiber content was more,while the shear strength was reduced after high temperature treatment.(4)The compressive constitutive model and tensile constitutive model of Hy F/HPCC considering temperature and fiber are established,respectively.The fitting equations of the peak compressive stress,peak compressive strain,elastic modulus,cracking stress,cracking strain,peak tensile stress,and peak tensile strain considering temperature and fiber are proposed,respectively.The single factor fitting equations of shear strength considering fiber factor at room temperature and considering temperature factor at different mix proportions are proposed respectively.It is found that constitutive models of Hy F/HPCC are in good agreement with the test curve,and the two-factor equations and univariate fitting equations can better predict the experimental results.