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Superplasticizers in Admixtures

Source: | Updated: Jan 29, 2016

A new type of water-reducer, the high-range water-reducing admixture or superplasticizer, debuted in North America in the mid-1970s. The March 1978 issue reported laboratory test results:

Superplasticized concretes show enormous increases in slump without any significant segregation.

The loss of slump with time is a serious limitation, but this can be minimized by adding superplasticizers to concrete at the jobsite.

The 28-day compressive strengths are equal to or greater than the corresponding strengths of the reference mix, whether or not compacted by vibration.

Superplasticizers are not economical for use in everyday concrete, but ideal for use in situations that demand flowing concretes at very low water-cement ratios.

Superplasticizers opened new possibilities for the use of silica fume, as reported in the May 1982 issue. Without the high-range water reducers, the use of silica fume was impractical because of its high water demand. The combination was found to produce ultra-high-strength concrete with compressive strengths exceeding 15,000 psi.

According to the article, “This of course is a very specialized area with limited applications.” But by March 1988, “[the] two developments have made possible the new generation of high-strength concrete now available for routine construction.”

The April 1985 issue reported on a new development: superplasticizers that provided a higher slump life and could therefore be added at the batch plant instead of on the job. An article in the March 1990 issue described “third generation” superplasticizers that maintained normal setting properties and still produced a low-water-cement-ratio concrete that would retain a high slump for an extended time.

During the 1990s, the polycarboxylate generation of superplasticizers helped make self-compacting concrete (SCC) a practical reality.

“Today many believe that SCC is the way of the future,” stated a March 2003 report, citing estimates that within three years, the portion of precast producers experimenting with and using SCC had grown from 10% to 90%.

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