As anyone who works with concrete will tell you, creating the right mix design is one of the most important, and often frustrating, parts of the job. The mix design not only dictates strength and durability, but also the consistency, pumpability, and finishabilty of the mix while in the plastic state. The mix design can also determine how the concrete will behave as it is setting up and how much bleed water will rise to the surface. In most cases, some bleed water is fine, but in mixes, with higher water-cement ratios the bleeding can be excessive. The excessiveness of the bleed water is what can cause problems.
What is Bleed Water?
Segregation in the concrete mix causes bleed water. As the concrete goes through the hydration process, the heavier particles tend to settle down to the bottom, forcing any free-floating water molecules to the surface. Bleed water has many causes, most of which are related to mix design. The main cause of bleeding in concrete is high-water cement ratios. Sometimes mixes arrive on site and are not the correct slump. Water gets added, increasing the water-cement ratios and the risk of bleeding. Mixes with coarse aggregates such as river rock or chip stone are also more likely to experience bleeding as these aggregates do not absorb as much moisture as materials like sand and cement.
Why is Bleed Water a Problem?
Excessive bleed water can create many long-term problems for the concrete, but perhaps the first challenge it presents is the delay in finishing. Troweling concrete with standing bleed water increases the risk of scaling, spalling, and crazing on the concrete finish. So the finisher must wait until most of the water has evaporated before any finishing tools touch the concrete surface. Aside from delays at the job site, excessive bleed water can increase the water-cement ratio at the surface of the concrete. As the water evaporates, it leaves voids that make the concrete more porous. This porosity provides pathways for moisture to find its way into the concrete in the future and is the cause of leaks in concrete buildings. As more water evaporates from the surface of the concrete, it also increases the risk of shrinkage cracks, which can diminish the concrete strength.
How to Reduce Bleed Water?
The easiest way to reduce bleed water in the concrete is to lower the water in the concrete mix. Working with higher slump concrete decreases the number of free water molecules rising to the top of the concrete. Adding fine materials, including cementitious materials or sands, can lower the risk of bleeding. Increasing the air content has also proven to be a good solution for reducing the amount of water pushed to the top of the concrete as it sets.
Can Admixtures Be Used to Reduce Bleed Water?
Concrete admixtures are an effective way to adjust the mix design of your concrete in a cost-effective, job-specific way. Fritz-Pak creates our powdered admixtures to add to the truck at the job site. We offer several admixtures that can help improve your mix designs to reduce the amount of water pooling on the surface of your concrete.
Superplasticizers: Often referred to as water-reducing admixtures, Fritz-Pak Superplasticizers can reduce the amount of water required in your concrete mixes by up to 40%. These powerful products improve the flow of your concrete to ensure you can meet slump specifications without extra water.
Air Entrainers: Fritz-Pak’s Air Plus and Super Air Plus offer up to 2% of natural air entrainment. Entrained air in concrete helps reduce bleed water because the even distribution of the air pockets prevents as much movement of the free water molecules, allowing them to stay in the mix and eventually bond with cement particles during the hydration process.
Viscosity Modifying Admixtures: VMAs, such as Fritz-Pak’s Super Slump Buster, can also help reduce bleed water in concrete. These products help improve the bond between the water molecules and the cement molecules. This reduces the number of free water molecules in the mix that would otherwise rise to the surface of the concrete.
Flowable Fill Admixture: Flowable fill, or controlled low-strength material, mixes can have extreme bleeding because of the low strength required. The extra water in the material creates high levels of bleeding. Fritz-Pak’s Fill Flow admixtures use a foaming agent to create hundreds of thousands of entrained air pockets. These air pockets help lower the strength of the mix without excess water and reduce the risk of bleeding.
For more information about how our products can improve your concrete, follow our social media channels. Don’t forget to shop the online store to order the products you need from your computer or smartphone.