Self-Consolidating Concrete Construction

Construction is where SCC really shines. What could be better than a mix that consolidates itself, eliminating all vibration, lift lines, and bugholes? For flatwork, SCC mixes can be described as self-leveling while formed concrete can be self-placing. Here are a few tips on construction with SCC:

  • SCC can be delivered in ready-mix trucks although the trucks will often not be completely full, since the SCC can slosh around in the truck and even slosh out. Trucks carrying SCC have even overturned when the full load shifted during a turn.
  • When placing SCC, it should be allowed to flow under its own weight from a single location if possible. SCC can flow horizontally as far as 33 feet or more. Walls and columns can even be pumped from the bottom up.
  • SCC pumps very easily and with reduced pumping pressures. Air content tends to remain more stable in an SCC mix during pumping than for conventional concrete.

iCrete
SCC easily flows around obstructions with no vibration needed. Joe Woolhead for iCrete

Formwork should be designed for full liquid head. This means that there will be another 150 pounds of pressure for each foot of height of the forms. This is a danger for SCC since it places so rapidly and can develop pressures leading to blowouts. Research is currently being done to determine if SCC doesn't begin to set up in the forms, which could reduce the required pressure capacity of the forms, but for now, it's always smarter to be conservative. There have been serious blowouts with SCC and contractors tell me that it will find and leak through even very small gaps in their formwork.

Dot for Dot
These elevator shafts were poured in a single lift using SCC, despite concern that the forms were not strong or tight enough to handle the pressure. Dot for Dot

  • All SCC is not the same, so have the ready mix company provide a mix that is right for your application. Specific applications may require more or less filling ability, passing ability, or stability.
  • Not only is vibration not necessary but can be damaging to SCC by causing segregation. To blend lifts, vibrators can be used but only for a few seconds.

Lafarge
Self-leveling slabs require only minimal finishing to get a flat floor. Lafarge Agilia

  • Slabs have not been a popular application of SCC—at least not prior to now. "We have helped develop self leveling mixes that are slightly less viscous but that need nearly no finishing," said Euclid's Caroline Talbot. "It's a niche market but growing. For small pours, driveways and such, the extra QC and cost may not be worth it, but for commercial slabs or floors for buildings, the self leveling concrete would be a big advantage." On floors that don't have high flatness tolerances, SCC can be placed with only minimal bullfloating. If applying a texture, even a broomed finish, don't start too soon or the concrete will slump back to a smooth surface.
  • Curing is important for SCC since it is so often a low water-cement ratio mix. Low water mixes can develop autogenous shrinkage, where the unhydrated cement consumes all of the water in the concrete matrix. Wet curing is best, but at least apply a curing compound to protect the surface from drying out.

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