Q. Mechanism of plastic settlement in fresh concrete?

Within a few hours after placing of fresh concrete, plastic concrete can experience cracking due to occurrence of plastic settlement andplastic shrinkage. The cause of plastic settlement is related to bleeding of fresh concrete. Bleeding denotesto migration of water to the top of concrete and movement of solid particles to bottom of fresh concrete. Expulsion of water at the time of bleeding outcomes in the reduction of the volume of fresh concrete. This persuades a downward movement of wet concrete. If such kind of movement is hindered by the presence of obstacles such as steel reinforcement, cracks will be formed.