Experimental Investigation on the Grey Correlation Degree between Macroscopic Properties and Pore Structure of Hybrid Fiber Reinforced Concrete Under Salt-Freezing

Salt-freezing action is one of the main causative factors in the deterioration of concrete structures. Currently, there are severe challenges in quantitatively characterizing the relationship between macroscopic and microscopic parameters of concrete structures. In this work, in combination with the macro-microstructure tests of basalt and polypropylene hybrid fiber reinforced concrete (BPFC) under alternating action of salt-freezing (ASF) cycles, we investigated the deterioration characteristics of macro-mechanical properties and the microstructure pore of the BPFC with different fiber dosages when subjected to the ASF. By constituting a three-dimensional reconstructed model of the BPFC, the grey entropy correlation degrees between the fine pore structure and macroscopic properties were proposed. The results indicate that mechanical properties of BPFC achieves optimal performance when basalt fiber and polypropylene fiber are doped at 0.15% and 0.1%, respectively, suffering from ASF cycles. With the boost of ASF cycles, the peak stress diminishes and the peak strain inversely rises under uniaxial compression and split tensile of BPFC specimens. Under the ASF, the internal pore size distribution of BPFC exhibits a pronounced trend of lognormal distribution, with an uninterrupted raising in its porosity and a gradual downregulation in its pore fractal dimension. The gray entropy correlation analysis indicates that the strength of the correlation between three pore structure parameters considered and macroscopic mechanical parameters is ranked in the following order: fractal dimension, average pore diameter, and porosity. The research sheds new light on a valuable theoretical foundation for promoting the performance and assessing the durability of hydraulic concrete in frigid and dry regions.