Title:
Early Thermal Cracking of Concrete - A Case History
Author(s):
H. W. Chung, P. K. K. Lee, and D. Ho
Publication:
Concrete International
Volume:
7
Issue:
5
Appears on pages(s):
36-38
Keywords:
beams (supports); contraction; cracking
(fracturing); form removal; heat of hydration; hot
weather construction; reinforced concrete; thermal
expansion.
DOI:
Date:
5/1/1985
Abstract:
An investigation into the cause of cracking of a new railroad station is described. A large number of cracks was discovered upon removal of formwork. The cracks developed in the reinforced concrete beams, some ex-tending into the adjoining slabs above. Structural calculations indicate that the multitude and extent of cracking could not have been caused by the self-weight of the concrete beams, despite the long spans and the marginal concrete strength. In situ measurements of vibrations induced by the passage of nonstop trains also excluded the possibility of loosening of the shoring or formwork. Site records show that concreting was carried out in hot weather when the temperature was in the high thirties C (high nineties F). With a rather high cement content, the heat of hydration of cement could have raised the temperature of the concrete 30 C (54 F) above the ambient temperature. When the concrete subsequently cooled down, the thermal movement manifested itself in the form of cracking on those members with substantial end restraint. Theoretical estimation of crack spacing agrees with observation. Some of the cracks were monitored with glass telltales. No further widening of the cracks was observed. The structure was subsequently repaired by epoxy injection.