Shrinkage of concrete refers to the reduction in volume that occurs as the concrete dries and loses moisture over time. This phenomenon is primarily caused by the loss of water that is not chemically bound within the hydration products of the cement. There are several types of shrinkage in concrete: plastic shrinkage, which occurs shortly after placement; drying shrinkage, which happens as the concrete hardens and dries over time; and autogenous shrinkage, which results from the hydration process itself. The mechanism behind shrinkage is largely due to the capillary forces in the pore structure of the concrete, which pull the solid particles closer together as moisture evaporates.