Experimental Research on the Mechanical Properties of Steel Fiber-Reinforced Concrete Under Freeze-Thaw Cycles

Freeze-thaw （F-T） resistance tests were conducted on eight groups of steel fiber-reinforced concrete （SFRC） with different strength grades. The effects of concrete strength and the number of F-T cycles on the compressive strength， mass loss rate， relative dynamic elastic modulus （RDEM）， and microstructural evolution of SFRC were investigated. An F-T damage model based on RDEM was established， and the service life of SFRC in typical cold regions was predicted. The results indicated that low-strength SFRC （C30， C40） exhibited significant F-T damage， with pronounced surface spalling， exposed aggregates， and through-thickness microcracking. After 125 F-T cycles， the compressive strength loss rates reached 35.02% and 31.65%， respectively. In contrast， high-strength SFRC （C50， C60） maintained better integrity， with strength loss rates below 9.61%. Mass loss and RDEM degradation increased progressively with F-T cycles， while high-strength SFRC demonstrated superior F-T resistance. Scanning electron microscopy revealed denser matrix structures in high-strength SFRC compared to low-strength specimens. The RDEM-based damage model achieved a coefficient of determination （<italic>R</italic>²） exceeding 0.994， accurately capturing the evolution of mechanical properties in SFRC under F-T cycles. Service life predictions suggest that C60 SFRC can achieve a maximum service life of up to 19.7 years in cold regions.