Impact behavior and damage mechanisms of low-fiber-volume fiber-reinforced cementitious composites after high-temperature damage

This paper investigates the damage mechanisms of fiber-reinforced cementitious composites (FRCC) under impact loading after high-temperature exposure. The effects of hybrid fiber systems were investigated using three types of fibers, including basalt fiber (BF), polyvinyl alcohol (PVA) fiber and ultrafine-grained ceramic composite (FC). The investigated mixtures contained a total fiber volume fraction of 1% and were classified as low-fiber-volume FRCC. The impact performance of FRCC after exposure to various temperatures was systematically studied using a drop-weight impact test system. Before testing, the specimens were oven-dried at 50 ± 5 °C until constant mass was achieved. They were then heated from ambient temperature (20 ± 5 °C) to target temperatures of 200 °C, 400 °C, 600 °C, and 800 °C at a linear heating rate of 10 °C/min. After reaching the target temperature, the specimens were held for 2 h and then naturally cooled to room temperature. Furthermore, the two-parameter Weibull distribution was adopted to analyze the variation patterns of FRCC from the perspective of reliability functions. Moreover, the cracking area ratio and fractal dimension were used to quantitatively investigate the failure characteristics of FRCC. The obtained results indicate that the gradual decline in the impact resistance of FRCC with increasing temperature is attributed to the dehydration of hydration products and fiber melting. The hybrid group with a 1:1 vol ratio of BF to PVA fiber exhibits the optimal impact resistance. Its first-crack impact energy increases by 75% compared with the PVA-only fiber group, while the initial crack width and crack area are reduced by 6.5% and 9.5%, respectively. Fiber pull-out and fiber melting are the typical failure modes before and after high-temperature exposure under impact loading, respectively.