Heat of hydration can be problematic in deep pours as it
can cause large differential temperature gradients between the centre and the
surface of deep concrete members; leading to thermal cracking.
Another problem associated with the heat of hydration in
concrete floor slabs is early thermal shrinkage. This is where the concrete
maintains a much higher temperature than its surroundings as it is hydrating
quickly in the early phases of its strength development. After the concrete has
set, hydration starts to slow down and cool to the ambient temperature. This
will cause the slab to shrink and, if restrained, crack.
In Portland cement
the gypsum component is responsible for the steady hydration of the concrete;
in turn ensuring undesirable temperatures aren’t reached. The peak temperature
reached in a slab can be reduced by using cement replacing materials which
hydrate more slowly, such as GGBFS.