Research on a sustainable concrete synergistic reinforced with carbon fiber and carbon nanofiber: Mechanical properties, durability and environmental evaluation

Abstract

A sustainable concrete was developed by incorporating carbon fiber (CF) and carbon nanofiber (CNF), where the synergistic modification effect of micro-scale and nano-scale of fibers was exploited and the mechanical properties and durability of concrete were improved. The mechanical test, shrinkage test, freeze-thaw cycle test, water permeability test and carbonation test were conducted on carbon fiber/carbon nanofiber reinforced concrete (CF/CNFRC) with different mix proportions. The results show that, when the content ratio of CF to CNF is 1:3, the compressive strength, splitting tensile strength and flexural strength are increased by 14.12%, 21.46% and 18.05% compared with plain concrete (PC). At the same time, the shrinkage rate at 180-day age, relative permeability coefficient, compressive strength loss rate at 200 freeze-thaw cycles and carbonation depth at carbonation age of 28 days are reduced by 30.57%, 66.56%, 37.72% and 34.09% respectively, at which time CF and CNF have the best synergistic modification effect. Durability value was further introduced to quantitatively evaluate the durability of CF/CNFRC, showing that the durability value of CF/CNFRC01 was the largest and increases by 57% compared with PC. Through MIP and SEM tests, the microstructure of CF/CNFRC was analyzed, and the multiscale synergistic modification mechanism of CF and CNF was further explored. Compared with the single CNF, appropriate amounts of CF and CNF can exert a positive multiscale synergistic effect, which further optimizes the pore structure through fiber bridging and filling, inhibits crack propagation, improves the compactness and integrity, and thus improves the mechanical properties and durability of concrete. In addition, the economic and environmental benefits of CN/CNFRC were discussed by calculating the cost-benefit ratio and CE-benefit ratio (the ratio of CO2 emissions to durability benefits). The calculation results show that CN/CNFRC has the best economic and environmental benefits when the content ratio of CF to CNF is 1:3, where the environmental benefits are 31% higher than that of PC.