Cooling and Insulating Systems for Mass Concrete

Description

The need to control volume change induced primarily by temperature change in mass concrete often requires cooling and insulating systems. This report discusses three construction procedures used to control temperature changes in concrete structures: precooling of materials, post cooling of in-place concrete by embedded pipes, and surface insulation.

Other design and construction practices, such as selection of cementing materials, aggregates, chemical admixtures, cement content, or strength requirements, are not within the scope of this report. The objective of this report is to offer guidance on the selection and application of these procedures for reducing thermal cracking in all types of concrete structures.

Major developments in cooling and insulating systems for concrete began with post cooling systems for dams. Later gains were made in developing precooling methods. The use of natural cooling methods has increased with the use of better analytical methods to compute thermal performance. Similarly, insulating systems expanded beyond just cold weather protection and into control of thermal gradients during other weather conditions. The first major use of post cooling of in-place mass concrete was in the construction of the Bureau of Reclama-tion’s Hoover Dam in the early 1930s. The primary objective was to accelerate thermal contraction of the concrete mono-liths within the dam so that the contraction joints could be filled with grout to ensure monolithic action of the dam.

Cooling was achieved by circulating cold water through pipes embedded in the concrete. Circulation of water was usually started several weeks or more after the concrete had been placed. Since the construction of Hoover Dam, the same basic system of post cooling has been used in the construction of many large dams and other massive structures, such as power-houses, except that circulation of cooling water is now typically initiated immediately after placing the concrete