Concrete Bleeding

Water being the lightest ingredient of all the other materials in concrete, bleeding, i.e., the upward movement of water when concrete settle downwards, is natural in concrete. The bleeding water, in certain situations emerges at the surface and in some other situations may not come up to the surface. But bleeding does take place.

The bleeding water gets trapped by flat or flaky pieces of aggregates and also by reinforcement and gets accumulated below such aggregates and reinforcement. This is known as internal bleeding. In addition to internal bleeding, the water may further emerge out and accumulate on the top surface of concrete.

Firstly the internal bleeding water trapped below flat pieces of aggregate and reinforcement affect the bond between hardened cement paste, (hcp) and aggregate or reinforcement on account of local higher W/C ratio. The interface is easily prone to micro cracking due to shrinkage stresses caused on dissipation of heat of hydration and drying shrinkage. The interface becomes a weak link in concrete. On loading, the micro cracks propagate further, making the concrete susceptible to degradation by environmental agencies.

The bleeding water, emerged at the top surface of concrete, when evaporates make the top surface porous, having very little abrasion resistances. Often, masons float the concrete when bleeding water is still standing on the surface. Too much working of the top surface presses the coarse aggregate down and brings up fine particles of cement and water. Such top surface made up of too fine materials with excess water develops cracks and craziness, affecting durability of concrete.