Valorization of waste GFRP composites in sustainable cement mortar: enhancing resistance to coupled sulfate freeze-thaw damage

The recycling and reuse of waste glass fiber reinforced polymers (GFRP) is very difficult. This study employed mechanical crushing and graded screening to separate and prepare recycled glass fibers (RGF) and recycled powder (GFRP-RP).Systematically investigated the mechanism by which GFRP-RP can be used as an auxiliary cementitious material to replace cement, as well as the effect of mixing RGF with chopped glass fibers (GF) at a 1:1 volume ratio with total hybrid glass fiber volume contents of 1.0%, 1.5%, and 2.0%. Through mechanical property testing, coupled freeze-thaw sulfate erosion testing, and scanning electron microscopy (SEM) analysis, the following conclusions were drawn: The blended glass fibers exhibited a synergistic reinforcement mechanism, with optimal synergistic effects achieved at a total fiber content of 1.5% and a GF:RGF blend ratio of 0.75% each; When the replacement rate of GFRP-RP was ≤ 10%, the microfilling effect and superhydrophobicity (static water contact angle = 152.3 ± 2.1°) of GFRP-RP reduced mortar porosity and water absorption, decreased free water content, and blocked sulfate erosion pathways, among which RP5GF0.75RGF0.75 exhibited the best sulfate-freeze-thaw resistance, achieving a compressive strength retention rate of 85.23%, a relative dynamic modulus of elasticity reduction of 19.16% after 50 sulfate freeze-thaw cycles, with average damage level of 29.52%.