Investigation of effects of bonding agent on performance of cold joint in concrete member

Abstract

One of the most common difficulties in the execution of concrete structures is cold joint because of delay in concrete casting due to several circumstances as well as improper casting sequence. The discontinuity in concrete element leads to structural weakness, increasing the permeability, corrosion of the reinforcement, reducing the durability and bad appearance of concrete. In this research, the aim to eliminate the cold joint by applying the bonding agent. In order to evaluate the effect of the bonding agent on cold joint, 76 number of cubes were cast using grade 30 concrete. Out of them, 36 specimens contain cold joint with 20° degree of inclination to the horizontal plane for compressive strength with and without applying bonding agent other 36 specimens had cold joint in the horizontal plane for splitting tensile strength with and without applying bonding agent and considered delay time of one hour interval up to 5 hours. After 28 days of curing, all specimens were tested as per standard method. The experimental result of compressive strength shows that cold joint with applying bonding agent give 6% improvement as compare to without applying bonding agent. But, the experimental result of splitting tensile strength shows that no considerable influence on cold joint as applying bonding agent compare to without applying bonding agent. However, there is considerable reduction in the compressive strength (30.50%) and tensile strength (33.14%) compare with initial specimens with applying bonding agent. Further, observation based on failure surface of tested specimens clearly indicated that, there are no aggregate inter logged in between two layers when delay time past the initial setting time of the first layer. So, the reduction in strength due to the cold joint purely depends on aggregate interlocking. The better options are to avoid the cold joint by using admixtures (retarders) to increase the initial setting time, adopt proper casting sequences and vibrate the layers together even within the initial setting time.