Concrete is subject to a number of problems in the time between being poured and having cured fully. Perhaps the most common of these problems is known as concrete bleeding. If you would like to improve your understanding about this unwelcome phenomenon, read on. This article will discuss why it occurs, and what you can do to prevent it.
Concrete bleeding falls under the larger subset of concrete segregation. Segregation is distinguished by the fact that it involves the separation of one or more of the concrete's basic ingredients--i.e. cement, aggregate, and water. This separation tends to occur in the early stages of curing, soon after the concrete has been poured. Bleeding is the phenomenon by which water separates from the cement and rises to the top of the curing concrete.
Bleeding is not a problem when a particular batch of concrete has been properly proportioned and mixed. It is more likely to become an issue when the mix included an excessive amount of water. Here the concrete is simply too diluted to retain its proper adhesion. As a result, the water tends to rise to the top, since it is the ingredient with the lowest specific gravity.
Concrete bleeding may occur even when water has been added in an appropriate proportion. This is often the result of insufficient mixing. In other words, the water has not been integrated thoroughly enough with the cement to prevent its premature separation. Likewise, bleeding is more likely to occur when using a large size of aggregate, since this aggregate will display an increased tendency to sink toward the bottom of even well-mixed concrete.
Why Concrete Bleeding Is Bad
To understand why bleeding presents such a problematic scenario, it helps to envision the changes that will take place as the water migrates upward toward the surface. This movement results in the creation of minute channels as the water is forced to navigate around aggregate particles.
Because the resulting concrete is too thick to easily flow back into these channels, they tend to remain present even after the concrete is cured. At that point they greatly decrease the overall strength of the concrete, increasing the chances that damage will occur as the result of heavy weight and other structural stresses.
How To Prevent Bleeding
As you might have deduced by now, there are two effective ways to prevent bleeding. The first is to be especially careful when calculating the amount of water that needs to be added. The second is to be sure not to under mix the concrete. Likewise, utilizing a smaller sized aggregate will help to prevent the problem from occurring.
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