On High-Temperature Properties of Structural Shotcrete Containing Different Accelerating Agents

Shotcrete has been increasingly used in the past years as a structural material for the construction of the final lining in blasted tunnels, and a number of subway, pilot and service tunnels demonstrates the reliability of this technique. To consider shotcrete as a true structural material, however, its fire resistance should be ascertained, something not adequately done so far. In this project, three mixes (C1 containing an accelerating agent based on sodium-silicates, and C2F/C2 with/without steel fibers containing sulpho-aluminates) are thermally and mechanically characterized after being exposed to high temperature. The results show that (a) the alkali-based mix is more temperature-sensitive than the alkali-free mixes; (b) alkali-free mixes are less porous, but steel fibers increase their porosity; (c) the thermal diffusivity decreases with the introduction of the fibers and with the use of alkali-based agents; and (d) there are no major differences between the high-temperature mechanical behaviors of ordinary vibrated concrete and alkali-free shotcretes.