Objective To improve the durability of shotcrete in high-altitude and cold regions and to address issues such as cracking and poor frost resistance of ordinary shotcrete in freeze-thaw environments.Methods With the method of adding mixed fibers to shotcrete,the relative longitudinal wave velocity,relative compressive tensile strength and changes in internal pore structure of sprayed mixed fiber concrete under different freeze-thaw cycles were studied by combining freeze-thaw cycle experiments,ultrasonic detection experiments,compressive tensile performance tests and pore structure tests.Multiple evaluations were conducted on the freeze-thaw damage of specimens based on their compressive and tensile performance damage levels.The relationship between the con-tribution rates of steel fibers and polypropylene fibers and the compressive strength of shotcrete was analyzed and a freeze-thaw damage model of shotcrete was established based on the formula for the contribution rates of steel fibers and polypropylene fibers.Results Compared with the single steel fiber and polypropylene fiber specimens,the compressive strength loss of shotcrete specimens mixed with 1％steel fiber and 0.1％polypropylene fiber decreased by 7.5％and 33.3％respectively,and its splitting tensile strength loss decreased by 15.6％and 35.0％respectively.At the chord length dimension of 0.1mm＜d＜1mm,the frequency of bubble chord length in the mixed addition of 0.1％polypropylene and 1％steel fiber shotcrete decreased by 24.9％and 27.3％respectively,compared to the single addition of 1％steel fiber shotcrete and 0.1％polypropylene shotcrete.The research found that the contribution rates of steel fibers and polypropylene fibers to compressive strength showed a trend of first increasing and then decreasing.The freeze-thaw damage model was established based on the contribution rates of steel fibers and polypropylene fibers.Conclusion The mechanical properties of sprayed hybrid fiber reinforced concrete are low in loss and less prone to cracking and have good frost resistance,providing a theoretical reference for shot-crete structures in high-altitude and cold regions.
shotcretesteel fiberpolypropylene fibercompression and tensile performancepore structuredamage model
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