Actions during hardening
One of the major difficulties with concrete as a construction material is the volume instability as a function of time. Due to several phenomena, often occurring simultaneously, the dimensions of a concrete element evolve in time even without external mechanical loading. When the resulting deformations are restrained, cracking and damage can occur in the structural concrete element. Especially during the hardening process, the cracking risk can be quite high, because in this stage the young concrete already has a relatively high stiffness and still a relatively low strength (see also Chapter 1).