Of the various problems that can affect curing concrete, segregation is one of the most serious. Yet even within the concrete industry, many people still don't possess a thorough understanding of this problem. If you would like to learn more about what this problem means, as well as how to prevent it, read on. This article will provide a useful introduction to the issue of concrete segregation.
The Basic Idea
Put simply, segregation denotes the unwanted separation of the constituent elements of which concrete is composed. This tends to occur as the freshly poured concrete begins to settle. What usually happens is that the stone aggregate, being denser than the surrounding mixture of cement and water, sinks downward through the concrete. Once this process has started, there are not many things that can be done to reverse it. The resulting concrete tends to be more susceptible to degradation, cracking, and wear.
There are a number of different causes of concrete segregation. The most frequent cause is a poorly proportioned mix—one that generally involves an excessive amount of water having been added. The over-diluted mixture of water and cement simply doesn't provide the support necessary to keep the aggregate suspended. This leads the accumulation of aggregate at the bottom of the concrete, and that leaves the upper portion greatly weakened.
Even if the water ratio is correct, segregation may occur if an inappropriate size or style of aggregate is used. That's because heavier or denser aggregate will display a greater tendency to sink downward. Concrete that has been mixed properly using an appropriately sized aggregate can also experience segregation. This tends to be the result of an excessive pour height. In other words, there is too great a distance between the end of the concrete chute and the surface of the pouring area.
A greater pour height means that the concrete will strike the ground with a higher velocity. This acts to push the heavier aggregate down to the bottom of the concrete while likewise forcing water to rise to the top. To minimize the likelihood of segregation, the pour height should be kept as low as possible.
Symptoms of Segregated Concrete
As noted above, the problems that can ensue from segregated concrete are numerous. As time goes on, such concrete will possess a much higher chance of succumbing to forms of damage such as cracking, raveling, and spalling. This damage will be especially noticeable on the surface owing to the non-homogenous constitution of segregated concrete.
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3 November 2016
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