Fires in buildings, bridges and tunnels can subject the surrounding structure to temperatures as high as 1300°C (Maraveas and Vrakas, 2014). The mechanical properties of conventional concrete deteriorate with increasing temperature. The compressive strength of concrete is reduced to about 75% and 15% of its ambient-temperature strength at 400°C and 800°C, respectively (CEN, 2004).
The mechanical behavior of Fiber-Reinforced Concretes (FRC) at ambient and high temperatures has been shown to be better than conventional concrete. Strain Hardening Cementitious Composites (SHCC) are a special class of FRCs that exhibit strain-hardening behavior under direct tension. In recent years, researchers have shown SHCCs to have significantly better mechanical behavior than ordinary FRCs at high temperatures. A retention of about 95% of the ambient temperature compressive strength has been reported when SHCCs were subjected to 400°C (Sahmaran et al., 2011). The primary mechanism for this improved behavior has been the melting of polymer fibers, which leaves a network of channels for easier escape of steam from the hardened cement paste at elevated temperatures.
In a recent study, attention was focused on capturing the effects of high temperatures on the bond behavior of SHCC with rebar, in addition to compressive and tensile strengths (Kumar et al., 2018). SHCC anchorage bond, tensile and compressive strengths when subjected to elevated temperatures, were significantly greater than those obtained for conventional concretes.
The benefits of polymer fibers on tensile strength of concrete are lost after they melt, at about 200°C. Steel fibers, which have a much higher melting point, of about 1300°C, can be used in conjunction with polymer fibers to improve the behavior of SHCCs further. Through recent efforts, a hybrid fiber-reinforced SHCC, that uses both steel and polymer fibers, has been developed (Deshpande et al., 2017). The newly developed material exhibits strain hardening behavior at ambient temperatures and retains significantly higher proportions of ambient-temperature compressive, tensile and bond (with rebar) strengths at elevated temperatures, as compared to conventional concrete and polymer SHCCs.
It is expected that these studies will facilitate the use of SHCC as a robust alternative to conventional concrete, especially for improving structural fire-resistance.
1. European Committee for Standardization (CEN). (2004). EN 1992-1-2:2004. Brussels, Belgium.
2. Deshpande, A. A., Kumar, D., Mourougassamy, A. and Ranade, R. (2017). "Development of a Steel-PVA Hybrid Fiber SHCC." In V. Mechtcherine, V. Slowik and P. Kabele (Eds.), SHCC4 (pp. 195-202). Dordrecht: Springer Netherlands.
3. Kumar, D., Deshpande, A. A., Ranade, R. and Elhami Khorasani, N. (2018). "Effects of elevated temperatures on residual bond strength of steel rebar with SHCC." 3rd R.N. Raikar Conference, Mumbai, India.
4. Maraveas, C. and Vrakas, A. A. (2014). "Design of concrete tunnel linings for fire safety." Structural Engineering International, 24(3), 319-329.
Sahmaran, M., Ozbay, E., Yucel, H. E., Lachemi, M. and Li, V. C. (2011). "Effect of fly ash and PVA fiber on microstructural damage and residual properties of ECC exposed to high temperatures." Journal of Materials in Civil Engineering, 23(12), 1735-1745.