What is concrete bleeding? It occurs when water is forced to the surface of the concrete. A concrete producer’s goal is to make concrete that does not feature excess concrete bleeding. Here’s how that’s done.
Concrete manufacturers must understand all the different variables regarding concrete and its properties under a variety of conditions. These conditions are often part and parcel of the manufacturing process itself. They include segregation, concrete mixes, water mixes, and aggregates (fine aggregates and coarse aggregates).
Although the proportions can and do vary, the basic ingredients of concrete are gravel (about 40%), sand (about 30%), water and air (about 20%), and cement (about 10%). You may often hear this referred to as the 10-20-30-40 rule.
During production, cement and aggregate (the gravel and sand) settle on the bottom and the water will be pushed to the surface. That water on the surface is the bleed.
We can limit this by sticking to the following two tried-and-true rules of concrete bleeding maintenance.
Add sand and air entrainment
Air entrainment is the addition of air bubbles into the concrete using a chemical surfactant, a type of detergent. This process increases the concrete’s durability. Meanwhile, sand will absorb water, which also limits concrete bleeding.
The combination of sand and air entrainment helps with the absorption of water. In other words, it limits the amount of water that rises to the surface of the concrete. If concrete bleeding isn’t taken care of, the concrete will be weakened.
Cement and water ratios
The ideal water-to-cement ratio is typically between 0.40 and 0.50. This is ideal because it makes the concrete workable while limiting the amount of concrete bleeding.
Concrete producers also understand by reducing water content in the mix itself can also assist in the absorption of excess water.
Concrete bleeding is a normal, physical process. The implementation of measures to avoid it will ensure your concrete products are built to last. Excessive bleeding means more free water at the top layer. Limiting bleed rate in freshly placed concrete before finishing operations means paying close attention to the weak top surface, the finer particles, and the free water.
Get in touch with Columbia Precast Products if you have any questions or comments about how to reduce bleeding in concrete.