ABSTRACT
As Fourier said, ‘nature is oblivious to the difficulties that it poses for mathematicians’. Similarly, sprayed concrete is blissfully unaware of the headaches it causes tunnel engineers. As explained in Section 2.2, sprayed concrete exhibits complex behaviour:
• the mechanical properties of sprayed concrete change considerably as the hydration reaction proceeds and a hardened concrete is formed (i.e. it ages);
• the rate of change of properties is rapid initially, due to the accelerated hydration, and slows with age;
• in its hardened (and hardening) form, sprayed concrete is a nonlinear elastoplastic material when under compression;
• in tension it is initially a linear elastic material which then fails in a brittle manner;
• to overcome the brittle failure, tensile reinforcement is often added; • sprayed concrete exhibits shrinkage; • the creep behaviour of sprayed concrete can be pronounced and changes
with age.
