What is Self-Consolidating Concrete?

Let's start with the simple definition and then kick it up a notch. SCC is very flowable concrete that never needs to be consolidated to fill forms or flow. Placed flat, like for a slab, it is virtually self-leveling. It looks a little like lumpy pancake batter. The consistency is measured by what's called slump flow, where we measure the width of the puddle left when a slump cone is filled and lifted. Slump flow for SCC varies from 19 to 30 inches.

VIDEO: SCC – NO VIBRATON

Self-Consolidating Concrete flows easily between obstructions to fill a form without vibration. Thanks to Euclid Chemical for this video segment. — Length: 01:06

But self-consolidating concrete is NOT simply concrete that flows. If that's all there was to it, we could just use lots of water. The currently accepted definition of what makes good SCC has three parts:

  • High flowability—means it flows easily into the finest details of formwork or molds and around reinforcing under its own weight. This is also called workability or filling ability (meaning it fills a form easily).
  • Passing ability—is the ability to flow through tight spaces, like congested steel reinforcing bars or narrow spots in the formwork.
  • Stability—this is the big difference between SCC and simply wet sloppy concrete. Stability implies that even at very high slumps (or slump flows) the concrete doesn't segregate, that it remains homogenous and there is no separation of the aggregate from the cement paste. There are actually two kinds of stability: dynamic stability (meaning it stays stable while being transported and placed) and static stability (meaning it stays stable--the aggregate doesn't settle and it doesn't bleed excessively--while it is in the forms but not yet hardened).

Then, of course, there is SCC after it gets hard. And, magically, it is not much different than conventional concrete. In fact, since we use superplasticizers (high-range water reducers) to achieve the flowability, and lots of fines, we can often proportion the concrete for very low water-cement ratios and get very high strengths and low permeability.

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