Freeze-thaw durability and environmental performance of recycled aggregate concrete containing graphene oxide

Recycled aggregate concrete (RAC) is vulnerable to freeze-thaw damage because adhered old mortar and multiple interfacial regions facilitate pore coarsening and crack propagation. This study investigated whether graphene oxide (GO) could mitigate such damage while compensating for its additional production burdens. The compressive strengths of reference (Ref) and GO-modified RAC were first compared for fractal gradations of D = 2.3-2.8, after which D = 2.5 was selected for 0-30 freeze-thaw cycles. Macroscopic testing, quantitative BSE imaging, exploratory CNN analysis of local image patches, cyclic molecular simulations involving tensile loading and unloading, and a cradle-to-gate assessment normalized by residual compressive strength were integrated. Both mixtures attained their highest strength at D = 2.5 within the investigated range. After 30 cycles, the residual compressive strengths of Ref and GO-modified RAC were 12.217 and 17.500 MPa, respectively. GO therefore provided 43.3% higher residual strength and reduced strength loss from 52.3% to 44.5%. BSE observations and idealized molecular simulations were consistent with less coarsening of pores and defects, weaker deformation localization, and slower cyclic stiffness degradation. Under the baseline GO price of 40 USD/kg, the 30-cycle cost, GHG, and PED per unit residual strength were 8.92%, 28.63%, and 24.91% lower than those of Ref, respectively. Normalized GHG remained 28.42%-28.63% lower across the tested GO GHG scenarios, whereas normalized cost became 27.98% and 64.88% higher when the GO price increased to 120 and 200 USD/kg. GO improved residual load-bearing performance, although its economic viability depended strongly on price.