Investigation of the factors affecting the formation of cold joints in concrete

Abstract

Performance of concrete structures can be directly affected by the presence of a joint. These joints can be either intentional or unintentional. The intentional joints may be formed to make the construction sequence more convenient. Construction joints and movement joints are very good examples to illustrate the intentional joints in concrete structures. However there can be joints which are formed unintentionally and can affect the performance of the structure. Cold joints are such unintentional joints which occur due to the time lag of pouring consecutive layers of the concrete. This can be happened when the initial setting time o f the first layer has passed when pouring the second concrete layer. However there were hardly any researches carried out under this topic. Therefore, it was decided to carry out this research to find out the factors which affect the formation of cold joints in concrete. The procedure mentioned in ASTM C403-92 was followed to conduct the penetration resistance test to determine the initial setting time of concrete under laboratory conditions. Test methods were developed to check the influence of a cold joint on strength parameters such as tensile strength and shear strength of concrete at the cold joint. Concrete specimens with cold joint were prepared by varying the casting time of the second concrete layer. From results obtained, it was found that there is a significant reduction in tensile strength and shear strength due to the presence of a cold joint. Furthermore, it was found that a cold joint can be formed even within the initial setting time period if the successive layers of concrete are not vibrated together.