A long-term exposure test of reinforced concrete (RC) beams with different flexural loads in a tidal environment has been conducted by taking the influence of time-dependent chloride diffusivity into consideration. According to the calculated apparent chloride diffusion coefficients, a chloride transport model under the coupling stresses at different depths and chloride action was established. Results indicated that the influence of flexural loads on free chloride concentrations and apparent chloride diffusion coefficients was obvious in tensile concrete zones. However, it was not a simple inhibition in compressive concrete zones. When the flexural load is less than 30% of the ultimate bearing capacity ($F_{\max }$ ), its effect on apparent chloride diffusion coefficients in concrete is slight. However, when 45%–60% $F_{\max }$ is exerted, a critical compressive stress can be detected. After exceeding the critical compressive stress, the chloride transport in concrete will be accelerated. Moreover, when the flexural load reaches 60% $F_{\max }$ , the critical compressive stress of accelerating chloride transport, which is 5.848 MPa, that is, 20% of the cubic compressive strength ($f_{\mathrm{cu}}$ ), appears.

Concrete’s production causes pronounced environmental impacts. It is confirmed that adding basalt fiber (BF) into concrete can improve the mechanical properties and reduce the chloride diffusion coefficient of concrete. Moreover, research on the environmental impact of BF and its application in concrete has gradually emerged in recent years. However, there is little research on the chloride diffusivity of concrete structures with BF under the coupling interaction of external loads and chloride action. Therefore, at first, six beams were cast to obtain the depth-dependent chloride diffusivity of concrete under the coupling interaction of chloride penetration and 50% and 80% of the cracking capacity. Then, a functional unit (FU) combining durability, cracking capacity and volume was proposed to evaluate the sustainability of the concrete structure. In addition, three extra FUs (volume, considering volume and cracking capacity simultaneously and considering volume, cracking capacity and durability simultaneously) were also proposed and compared with the first FU. Results indicate that, regardless of the applied load level, the average chloride diffusion coefficient of a reinforced concrete (RC) beam with BF is larger than that of an ordinary RC beam. Moreover, the sorting of life cycle assessment (LCA) results will vary significantly with the different preset functional units. When taking the cracking capacity into consideration, adding BF into concrete is a suitable solution to improve the sustainability of RC beams.