Concrete Admixtures - Flowability

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Superplasticizers (High-Range Water Reducers) can make a low-to-normal slump concrete into a high-slump flowing concrete which can be placed with little or no vibration. However, the change in slump usually lasts only about 30 to 60 minutes depending upon the brand and dosage rate.

High-range water reducers fall into either ASTM C494 Type F or Type G classification. In either case, they can be used to produce very high slumps without segregation, an ideal situation where increased flowability is necessary due to congested reinforcement.

Other applications and benefits of high-range water reducers include:

  • difficult wall placements
  • narrow forms
  • sections with blockouts, penetrations, or embedded items
  • pumping high vertical distances
  • fast placement of concrete
  • increased lift heights and free fall distances

Note: The increased thinness of the concrete mix means that forms should be tight to prevent leakage even through small joints which can result in fins and discoloration.

Type F superplasticizers

Added at the job site and keep concrete flowable for a short period of time. At some point, the concrete will lose slump quickly.

Type G superplasticizers

Can be added either during batching or at the job site. This admixture will delay setting, but cause the concrete to be flowable for a longer period of time which could delay finishing. If haul times are particularly long, Type G can be added at the plant. However, if delivery is delayed too long, the effects can be diminished. Redosing is possible to regain the plasticity of the mix and manufacturers recommendations should be followed closely.

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