Microstructural and mechanical evolution of recycled fiber-reinforced tunnel slag concrete under wet-dry cycles

The rapid expansion of tunnel construction has generated large amounts of tunnel slag and waste geotechnical fibers (GF), posing challenges to environmental sustainability and resource efficiency. The effective reuse and recycling of these materials have become pivotal in current research. Notably, the fluctuating conditions of wet-dry cycles present critical challenges to structural durability and safety. To address this challenge, this work developed an innovative geotechnical fiber-reinforced slag concrete (GFSC) using recycled tunnel slag and waste GF. The compressive strength, split tensile strength, and axial compressive strength of this novel concrete were evaluated under dry-wet cycling, and their microstructural evolutions were thoroughly analyzed using MIP, SEM, and XRD techniques. The results reveal that incorporating 0.9 kg/m3 GF improves the densification of GFSC, reduces porosity, and significantly enhances both compressive and tensile strengths; after 45 wet-dry cycles, the optimal GF dosage effectively bonds with the cement matrix, forming a dense interfacial transition zone that boosts structural stability and resistance to variable environments. These findings provide insights into extending infrastructure lifespan and safety under harsh conditions while promoting sustainability through recycled materials in engineering.