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Self Compacting Concrete

usually, concrete which is united and poured into a frame, must be vibrated before it can be left to dry. The reason for this vibration is that normal concrete, when poured, will leave some air bubbles between pieces of aggregate, rebar, etc… This vibration is very work intensive, and requires a number of skilled workers to complete. In the late 1980′s, recognizing a diminishing skilled work force, able to work with concrete, as well as an increased demand in the need for strong, durable concrete, researches began studying ways in which concrete could be poured without this need for vibration. The result was self compacting concrete, which has also been called self consolidating concrete, high performance concrete, and more.

Self compacting concrete, if proven successful, would mean a much faster, cheaper method of pouring concrete, without a loss in structural integrity. In order to achieve this result, scientists developed a new form of concrete mixture. In order to avoid air pockets within a concrete structure, two goals needed to first be accomplished. First, there needed to be a lower percentage of aggregate in the concrete mixture. With less coarse aggregate, there would be a lower chance that air pockets would form between large rocks, and rebar. The second goal was to develop a more viscous paste, which could run more smoothly between the aggregate, again lowering the possibility of air bubbles being formed. To achieve this second goal, scientists employed the use of superplasticizers. A superplasticizer is an additive that, when added to the cement mixture, works to increase the fluidity, and viscosity of the resultant mortar.

Now that a form of concrete had been proposed which would self compact, mitigating the need for workers to vibrate the concrete, the question at hand was whether this concrete would be as strong as traditional concrete. The answer was that if an adequately viscous mortar was used, and if the water-cementitious ratio was correct, in combination with a proper coarseness of aggregate; self compacting concrete is just as strong, and durable as traditional concrete.

Since the development of self compacting concrete, a number of tests have been accepted as reasonable methods to judge a concrete mixture’s ability to self compact. By utilizing these tests, builders can be confident in the integrity of their structure built using self compacting concrete. These tests generally work by pouring the concrete mixture into a funnel. If the concrete mixture passes through the funnel, it is considered adequately able to self compact, and will continue on to its final destination, which is generally a frame where it is going to dry.

Since the conception of self compacting concrete, it has been widely used around the world. Some builders continue to vibrate their concrete, even if self compacting concrete is used, just to further increase the integrity of their structure. Not only did self compacting concrete produce a cheaper way of laying concrete, the result was a better concrete mixture, which has influenced almost every concrete structure we see today.