Mass Concrete:

Mass concrete can be defined as concrete which is placed in massive structures like dams, canal locks, bridge piers, etc. A large size aggregate (up to 150mm maximum size) and a low slump are adopted to reduce the quantity of cement in the mix to about 5 bags per cubic meter of mass concrete. The mix is relatively harsh and dry and hence requires power vibrators of the immersion type for compaction. This concrete is generally placed in open forms. The heat of hydration may lead to a considerable rise of temperature because of the large mass of the concrete. It gives output in extensive and serious shrinkage cracks. These shrinkage cracks can be prevented by using low cements and placed by continuous proper curing of concrete. Placing the concrete within shorter lifts and permitting several days before the placement of the next lift of concrete can help in the dissipation of heat. Circulation of cold water by the pipes buried in the concrete mass might prove useful. On the other hand, where possible, concreting can be done in the winter season such that the peak temperature in concrete can be lowered, or the aggregates may be cooled before use. Mass concrete develops relatively high strength during the first month because of the temperature rise due to heat of hydration. At later periods, strength will be less than that of a continuously cured concrete at normal temperatures. The volume changes of mass concrete during setting and hardening are very small but large creep can occur at later ages.