On Shotcrete Mechanical Behavior past Severe Heating

Shotcrete has been recently proposed as a structural material for the construction of the final lining in blasted tunnels. To have shotcrete accepted by designers and owners, how-ever, its water permeability should be increased – or guaranteed by appropriate means - and its fire resistance should be checked. Since no experimental results are available today on shotcrete exposed to high temperature, a project concerning three shotcretes has been recently financed at the Politecnico di Milano. (The first shotcrete contains silicates, while the second and third are alkali-free, with/without steel fibers, respectively). The results concerning the residual mechanical properties in compression clearly show that good alkali-free thermally-damaged shotcretes (fc = 45-50 MPa in virgin conditions) behave similarly to vibrated concrete, and that – as in vibrated concrete – steel fibers tend to decrease both the strength and the elastic modulus in virgin conditions. Steel fibers, however, make shotcrete marginally more heat-tolerant, and improve its ductility in compression.