Final answer:
When fresh concrete is poured on top of or next to concrete that has already begun to cure, it can result in a weak joint known as a cold joint. A cold joint occurs when the new concrete does not properly bond with the hardened concrete, leading to a weak spot in the structure.
Step-by-step explanation:
When fresh concrete is poured on top of or next to concrete that has already begun to cure, it can result in a weak joint known as a cold joint. A cold joint occurs when the new concrete does not properly bond with the hardened concrete, leading to a weak spot in the structure. This weak spot can be more likely to leak and can weaken the overall integrity of the surrounding wall.
One of the main reasons for a cold joint is the presence of a hardened, smooth surface on the existing concrete. Without proper preparation, the new concrete will struggle to adhere to this surface. Additionally, if the fresh concrete is poured too late after the initial concrete has begun to cure, the bonding process will be hindered. To prevent cold joints, it is important to properly prepare the surface of the existing concrete by roughening it and ensuring it is clean and free from any debris. It is also crucial to pour the fresh concrete within the proper time frame to ensure optimal bonding.