Concrete bleeding occurs when water is forced to the surface of the concrete.
Concrete consists of sand, stone, cement, and water. When cement and aggregate settle on the bottom, any excess water that is not absorbed by the cement and sand will move to the surface. This leaves a top surface of water on the concrete, which is called bleed water on the surface of freshly poured concrete.
When making concrete, the goal is to make concrete that does not have excessive bleeding. This requires extensive knowledge of concrete properties along with expertise in the various forms of segregation, concrete mixes, mixing water, fine aggregates, coarse aggregates, and more.
Here are some tips on how to avoid concrete bleeding.
Know your cement and water ratio and stick to it.
To hydrate or cure concrete, a water-cement ratio of about .40 to .50 is recommended. This makes the product more workable. If there is any more water added, it’s likely that it will cause a concrete bleed.
If you notice a bleed happening, reduce water content or add more cement to the mix design to help absorb the excess water.
Add sand and air entrainment to the mix.
Sand absorbs water, and it can reduce a bleed. Sand with finer particles allows for greater absorption, so make sure you are using the right type of sand.
You can also use air entrainment to help with water absorption. The particles here are air bubbles, which aids in boosting the amount of surface area that the cement and water need to cover in the mix. In other words, it will minimize the amount of free water that rises to the surface when pouring new concrete.
If a bleed does happen, don’t allow the concrete to proceed to the final stages. Simply be patient and allow for the water to evaporate.
If the bleed is there and the concrete finisher completes the job anyway, the water will stay on the top layer and the concrete will be significantly weakened.
Concrete bleeding happens regularly, but with the right management, it can be avoided or fixed.