Correlation between macroscopic properties and microscopic pore structure in steel-basalt hybrid fibers reinforced cementitious composites subjected to elevated temperatures

Steel-basalt hybrid fibers reinforced cementitious composites (SBFRCC) have excellent mechanical properties, and current studies mainly focused on the macroscopic or microscopic properties of SBFRCC at room temperature separately. However, the macroscopic and microscopic properties of SBFRCC subjected to elevated temperatures, especially their correlation relationships are still unclear. Hence, this study aims to investigate the macroscopic and microscopic properties and their correlation relationships of SBFRCC subjected to elevated temperatures. Firest, the mass loss rate, three-point bending, uniaxial compressive, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) tests were conducted subjected to elevated temperatures. Then, the cor-relations between mass loss rate, fracture, uniaxial compressive behavior and pore structure were analyzed based on a correlation analysis approach. The results show that steel fiber and basalt fiber can effectively restrict crack initiation and propagation subjected to elevated temperatures. Uniaxial compressive strength and elastic modulus decrease with temperature while peak strain increases below 600 degrees C and drops after 600 degrees C. With the increase of temperature, the gel pore and transitional pore decrease, the large pores increase, the porosity in-creases, and the pore structure is "coarsened" significantly. The correlation coefficient between uniaxial compression strength and porosity is the highest, and it is reasonable to use porosity to characterize the changes of uniaxial compressive strength subjected to elevated temperatures. Gel pore has the highest correlation with initiation fracture toughness while large pore has the highest correlation with mass loss rate, unstable fracture toughness, fracture energy, and elastic modulus. Gel pore directly affects the generation of cracks while large pore directly affects the propagation of cracks.