Importance of controlling temperature rise due to heat of hydration in massive concrete elements

Abstract

This paper mainly discusses the deterioration of concrete due to temperature rise in concrete as a result of heat of hydration of cement. When concrete is subjected to high temperature at early age, many physical and chemical changes of the hardened concrete can take place. Recently, severe cracking in some of the pile caps of bridge piers in southern highway project in Sri Lanka was reported. After extensive investigations, it was found that the main cause for cracking in those pile caps was due to an internal chemical reaction known as delayed ettringite formation (DEF). DEF is sometimes referred to as internal sulphate attack which is an internal swelling reaction of the concrete that occurs in the presence of water without any external ingress of sulphate. It is widely accepted that concrete subjected to high temperature at early age and exposed to moisture continuously or intermittently is likely to crack due to DEF. Experimental investigations also revealed that even when the concrete is subjected to high temperature over a short period during early age, there is a possibility of long term strength reduction and increase in permeability. Apart from maximum temperature rise, it is essential to control temperature gradient across thick concrete members like pile caps, deep beams, bridge piers, raft foundations and concrete dams to prevent cracking. There are many factors affecting early age temperature rise in concrete and subsequent cracking and other deterioration of concrete. Therefore it is a basic requirement to specify limiting temperatures for any major concrete construction and strictly adhering to the specification during construction in order to avoid expensive remedial actions to rectify damaged concrete due to thermal effects. Apart from controlling maximum temperature rise in concrete and composition of cement, use of fly ash or slag blended cement is effective inpreventing most of the problems associated with temperature rise in concrete.