Dynamic Characterization of Advanced Cementitious Composites in Design and Construction of Safe Tunnel

Fibres in High Performance Cementitious Composites are often used to improve impact and blast resistance due to their ability in energy absorption. In order to appreciate the real effectiveness in uniaxial tension behaviour at increasing strain rates, an experimental investigation is in progress, aimed to compare dynamic with static behaviour by using a modified Hopkinson bar for dynamic loadings and a conventional closed loop electromechanical press for static tests. Due to limitations imposed by dynamic loadings, small notched cylindrical specimens are considered. The specimens were cored by prismatic specimens previously subjected to third point bending tests. The material investigated was a steel fibre reinforced mortar used for the production of thin prefabricated roof elements. The main object of the research was to highlight the role of thermal damage in uniaxial tension at low and high strain rate loadings. Straight low carbon steel micro-fibres were used. The fibre content was 1.25 % and the mix design guaranteed a self compacting mixture. The results show that, despite the relative low fibre amount, the material is characterized by a hardening behaviour in quasi static tests at room conditions. Moreover, in low strain rate tests after high temperature exposure up to 600°C, the thermal damage progressively reduces the toughness and weakly increases the strength, while for high strain rate tests the peak strength is significantly increased, but such increase is accompanied by an abrupt post-peak softening branch.