Hot and Residual Behavior of Steel Fiber-Reinforced Structural Shotcrete exposed to High Temperature

Sprayed concrete (shotcrete) has been known for almost a century as a reliable and effective material for rock stabilization, fire proofing of metallic structures and jacketing of R/C members. Shotcrete structural utilization, however, has been very limited so far, but the situation is changing, as proposals have been lately put forward for the use of shotcrete in rather demanding structures, like the linings of blasted-off tunnels, where fire resistance is a must. The lack of information on shotcrete’s behavior at high temperature and past cooling is the starting point of this research project aimed to investigate the ther-mo-mechanical behavior of a number of shotcrete mixes (with alkaline or alkali-free accelerating agents, with or without steel fibers), in order to check whether – and to what extent – shotcrete’s temperature-triggered mechanical decay is similar to that of ordinary concrete. Here the compressive behavior of two alkali-free shotcrete mixes is examined at high temperature (hot tests, T = 20-600°C) and past cooling (residual tests, T = 20-750°C), and the thermal diffusivity is evaluated as well (T = 150-900°C). The two mixes (vf = 0, 0.4%, expected strength fc = 40 MPa) behave similarly to ordi-nary concrete, and exhibit a very low thermal diffusivity at any temperature.