Concrete cold joint formation in hot weather conditions

Abstract

The performance of a concrete structure can be greatly affected by the presence of a cold joint: it causes deterioration of steel reinforcement in concrete, strength reduction, and destruction of the aesthetic appearance of the concrete surface. Cold joint formation becomes more likely in hot weather conditions due to the rapid setting behaviour of the concrete. The objective of this study was to examine the effect of the ambient temperatures on cold joint formation relating to the penetration resistance. Cold joint formation was evaluated by determining the flexural strength of a cold-jointed concrete beam. Fresh concrete with initial temperatures of 25 C was tested under the ambient temperature conditions of 25 C and 45 C. The experimental results show that the cold joint forms when the delay in placement between two consecutive layers is less than the conventional initial setting time of concrete, measured according to ASTM C403 (i.e., 3.5 N/mm2 penetration resistance). It was found that cold joints form when the penetration resistance is greater than 0.5 N/mm2 and this penetration resistance is independent of the ambient temperature.