Experimental Study On Uniaxial Tension Performance Of Steel Fiber Reinforced Mortar Exposed To Elevated Temperatures

The reinforcing and toughening effects are effectively exerted by adding steel fiber to cement-based composite materials.The steel fiber can not noly improve the defects of low tensile strength,high brittleness and easy-cracking of cement-based materials,but also effectively resist the fire-induced spalling of the matrix at elevated temperatures.At present,there is scarcely published study reporting the direct tensile behavior of steel fiber reinforced cement-based composite materials exposed to elevated temperatures at home and abroad.It is of great significance to study the tensile properties of the composite materials exposed to elevated temperatures for improving fire resistance,disaster prevention and reinforcement of concrete after fire.The effects of fire simulation temperature,steel fiber type,fiber volume fraction and matrix strength grades on the tensile properties of steel fiber reinforced mortar(Fiber Reinforced Mortar,known as FRM for short)at room temperature and elevated temperatures were investigated by uniaxial tensile test.The main contents can be drawn as follows:(1)Through the uniaxial tensile test of 16 groups of dog bone-shaped specimens,the effects of steel fiber type,fiber volume fraction,cement grade and water/cement ratio on the tensile propreties(tensile strength,peak strain,tensile energy dissipation,elastic modulus and Poisson's ratio)of FRM at room temperature were discussed.(2)The effects of target temperature,steel fiber type,fiber volume fraction and water/cement ratio on the tensile propreties of FRM were investigated by 32 groups of uniaxial tensile tests of FRM exposed to elevated temperatures.Moreover,the significance of the factors on the tensile parameters of FRM at different temperatures was quantitatively analyzed.Through the regression analysis,the fitted formulas for tensile strength and elastic modulus with temperature of FRM exposed to elevated temperatures were proposed,respectively.(3)The effects of temperature and water/cement ratio on the mass loss ratio ofFRM exposed to elevated temperatures were studied,and the surface color,surface spalling and surface micro-crack of specimens were compared and analyzed.Moreover,the effects of elevated temperature on the mineral composition,microstructure and internal defects of FRM were investigated by XRD,SEM and CT,respectively.The mechanism of degradation of FRM exposed to elevated temperatures was revealed.(4)The effects of temperature,steel fiber type,fiber volume fraction and water/cement ratio on the tensile stress-strain curves and tensile energy dissipation of FRM were studied.