Guide to Mass Concrete

Description

Mass concrete is defined in ACI 116R as “any volume of concrete with dimensions large enough to require that measures be taken to cope with generation of heat from hydration of the cement and attendant volume change to minimize cracking.” The design of mass concrete structures is generally based on durability, economy, and thermal action, with strength often being a secondary, rather than a primary, concern.

The one characteristic that distinguishesmass concrete from other concrete work is thermal behavior.Because the cement-water reaction is exothermic by nature,the temperature rise within a large concrete mass, where theheat is not quickly dissipated, can be quite high. Significanttensile stresses and strains may result from the restrainedvolume change associated with a decline in temperature asheat of hydration is dissipated.

Measures should be taken where cracking due to thermal behavior may cause a loss ofstructural integrity and monolithic action, excessive seepageand shortening of the service life of the structure, or be aesthetically objectionable. Many of the principles in massconcrete practice can also be applied to general concrete work, whereby economic and other benefits may be realized. This document contains a history of the development ofmass concrete practice and a discussion of materials andconcrete mixture proportioning, properties, construction methods, and equipment.

This document covers traditionally placed and consolidated mass concrete, and does not cover roller-compacted concrete. Roller-compacted concrete is described in detail in ACI 207.5R.Mass concreting practices were developed largely from concrete dam construction, where temperature-relatedcracking was first identified. Temperature-related crackinghas also been experienced in other thick-section concrete structures, including mat foundations, pile caps, bridge piers,thick walls, and tunnel linings.