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Note how easily it flows, even around corners, without segregation. Thanks to BASF for video footage. Self-consolidating concrete SCC is recognized as one of the greatest advances in the concrete industry. Using new admixtures and some mix modifications, we can now produce concrete that flows easily without segregating where the coarse aggregate separates from the cement paste. Concrete that segregates loses strength and results in honeycombed areas next to the formwork. It is the self-consolidating nature of SCC that makes it so valuable in construction.

SCC can flow into very intricate forms or forms that have a lot of reinforcing bars rebar congestion and still leave no voids. Normal concrete would have to be heavily vibrated in those applications to work out all the entrapped air bubbles next to the forms and reinforcing and get the concrete to move in. SCC is very exceptionally 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.

Slump flow for SCC varies from 19 to 30 inches. However, self-consolidating concrete is NOT simply concrete that flows. Thanks to Euclid Chemical for this video segment.

The currently accepted definition of what makes good SCC has three parts: High flowability — 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 — 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. Once hardened, SCC 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.

Lafarge North America SCC and conventional concrete differ only in some minor proportioning modifications and a couple of admixtures.

Lafarge even has a name, Agila, for its proprietary SCC mix. This thickens the mix, keeping the coarse aggregate stable in the matrix and also contributes to slump flow. The water-cementitious materials ratio is often quite low-as low as 0. Viscosity-modifying admixture VMA increases the viscosity to keep the mix stable. Without a lot of powder in the mix, VMA is used to thicken the mix and prevent segregation.

High-range water reducers for SCC mixes have recently been mostly those based on polycarboxylates, which have an incredible ability to increase slump at low dosages. Polycarboxylates, though, have created problems with foaming and adding unwanted air to the mix, so a de-foaming agent is added. There have also been some problems with sudden slump loss. It is recommended that for longer haul distances, the producer should consider using a naphthalene-based HRWRA instead of polycarboxylate.

Keep in mind that SCC mixtures are a little complicated, requiring just the right balance between all the materials, water, and admixtures. Find more information on concrete mix design. Always experiment with a mix like this first before you start a job.

Note how there is no segregation, even on the leading edge of the concrete. The guy with the shovel was expecting to have to push the concrete into the footing but eventually he gave up.

The ultimate dream is being able to set up the forms then have the ready mix truck driver come and fill them up with no other workers on the job site. That may never happen, but SCC that has been properly proportioned and placed provides many advantages: Reduced labor since no vibration is needed for concrete in forms and little to no screeding is needed for flatwork.

Faster construction since the concrete places so quickly-a truckload can be discharged in as little as one minute! Extremely good finished surface quality — SCC can take on nearly a mirror-like surface and can produce concrete with very fine detail. This is really advantageous with sculptures and is why precasters love it so much.

It can even flow into negative draft areas. Self-Consolidating Concrete flows easily and rapidly from a ready mix truck. Lafarge Agilia Simpler to detail the reinforcing steel, since it can be fairly congested and still get completely filled with concrete.

Quieter job sites or precasting shops since there is no vibrator noise. The best approach to controlling the cost is to work with your ready-mix producer to get the optimum mix for the intended use.

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.

SCC easily flows around obstructions with no vibration needed. Joe Woolhead for iCrete 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 Self-leveling slabs require only minimal finishing to get a flat floor. Lafarge Agilia Formwork should be designed for full liquid head.

This means that there will be another 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. There have been serious blowouts with SCC and it has been known to find and leak through even very small gaps in their formwork.

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. Slabs have not been a popular application of SCC-at least not prior to now.

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. 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. It accepts color, either integral or dry shake, as easily as any concrete. SCC allows castings with this kind of detail. The high fluidity of SCC forces all of the air out the mold and results in perfect glassy surfaces. Remember, though, that with SCC any defect however slight in the forms will be directly reflected in the finished concrete.

Also carefully select your form release agents to prevent bugholes tiny entrapped air bubbles that cling to the form surfaces. In an article in Concrete Construction a study that concluded that the best form release was a reactive vegetable-based agent on a well-seasoned form.

Find more info on using SCC for precasting concrete and on setting up a precasting operation. SCC has also been used for concrete countertops-mostly successfully. When cast face down, the SCC can produce a glassy surface that may not need any polishing.

As with any concrete, experiment first to find the best mixes and techniques for your application. Experts advise that enough concrete for the entire countertop should be mixed in a single batch and placed in a single pour.

As with all SCC, it is best to pour from a single location and let the weight of the concrete push itself into the forms or molds. The primary test used in the field for SCC is slump flow, although there are other field tests currently in use. Here is a brief description of each-more information can be found in the appropriate ASTM test method.

When the cone is lifted, the SCC spreads out like pancake batter. The slump flow is measured as the diameter of the pancake. Typical SCC mixes have slump flows ranging from 18 to 30 inches. The slump flow test is run both with and without the J-Ring in place and the passing ability is the difference in slump flow. A difference greater than 2 inches indicates poor passing ability.

A T20 between 2 and 5 seconds is taken as a low viscosity concrete. Recently, pads with a printed inch circle have been developed to make this test easier.

ASTM A slump flow test is often performed with the slum cone upside down. Bill Palmer The T20 test measures viscosity by timing how many seconds it takes for the concrete to spread to 20 inches in diameter. The technician observes the concrete as it spreads out in the slump flow test. A number from 0 to 3 is assigned-0 for no segregation to 3 for obvious segregation and paste separation cement, water, and fines from the concrete matrix. A VSI of 0 or 1 indicates a stable mix, while a 2 or 3 is unstable.

Segregation probe-Not yet standardized, this test measures segregation by placing a thin wire ring atop the SCC and measuring how far it sinks into the concrete in two minutes. This test promises to provide a quantitative value for segregation potential. American Concrete Institute www.


ACI 237R-07

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ACI-237R-07 Self-Consolidating Concrete

Tetaur A nonmandatory appendix of ASTM C provides a procedure for a relative measurement of flow rate, viscosity, and stability. If you like to setup a quick demo, let us know at support madcad. After spreading ceases, two orthogonal diameters of the concrete patty are measured. Self-xonsolidating Compu-tecture, Inc. After 15 minutes, the mold is separated into three sections representing the top, middle, and bottom of the cylinder.

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