In the past large volume concrete pours with low cement content was associated largely with dams to provide weight rather than load-bearing capacity. However, large pours using higher cement contents have become common for general structural applications.
There can be no strict definition of what constitutes a large volume pour in terms of dimensions or volume. As a general guide, special considerations may need to be taken for pours in excess of 500mm thick.
One of the main concerns with large volume casting is the heat generated as the cement hydrates. This is an exothermic reaction and the heat developed can result in a temperature rise in excess of 50°C. In smaller pours the logistical problems are less onerous, but heat of hydration must still be considered when the cement content is higher than about 350kg/m3. Associated with this temperature rise are thermal stresses generated by restraint to thermal movement. This restraint may be either internal or external.
The Concrete Society Advice sheet gives details of the special considerations associated with large volume concrete construction together with basic information on selection of materials, concrete mix design and planning.