What Is Mass Concrete?

The concrete placed in different massive structures such as dams, bridge piers, canal locks, etc is known as mass concrete.

In mass concrete, larger size aggregates (up to 150 mm maximum) and low slump (very stiff consistency) are used to reduce the amount of cement in the concrete mix (normally 5 bags per m3 of mass concrete).

As the concrete is relatively dry and harsh, it needs immersion type of powder vibrators for full compaction. The concrete is normally placed in open forms. Due to the greater mass of the concrete, the heat of hydration (reaction between cement and water) may increase the temperature considerably.

These can be avoided by placing the concrete in shorter lifts and taking gaps of several days before the next lift. During concreting, cold water should be circulated through the pipes buried in the concrete mass may also be useful. If possible, concreting can be done in the winter season to lower the peak temperature in concrete. Alternatively, the aggregates may be cooled before using in the mix.

The high temperature due to the heat of hydration may result in an extensive and serious shrinkage in the mass concrete. The shrinkage cracks can be prevented by using low heat cement and by rapid curing of the concrete.

The early age strength is very high compared to later strength concrete cured at normal temperatures. During setting and hardening the volume change of mass concrete is very small but it can produce larger creep at a later stage.