About Concrete Joint
Generally, Bonding Agents are used in concrete where there is a requirement to join the old and the new concrete surfaces. It is also used to join the surfaces between the successive concrete layers.
The basic function of bonding agent is to increase the bond strength or let us say to strengthen the bond between the old and new concrete surface. The cement within a concrete mix does not have any natural bonding agent. Hence, when fresh concrete is poured on top of an existing layer of concrete, the existing and new poured concrete layer do not tend to join together. Once poured concrete layer is cured, the new concrete will simply settle on top as a separate layer. This will not create a strong bond between the two successive layers. Thus, when the two layers fail to behave like one unit, it will ultimately affect the performance and strength of the structure. A bonding agent (bonding adhesive) therefore needs to be applied onto the existing concrete surface so as to ensure that the fresh concrete successfully adheres.
The same is also true for floor repairs. The new concrete will not adhere to the old concrete without the help of a bonding adhesive if concrete without any bonding agent is used to fill gaps caused by damage.