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Polycarboxylates and SCC

Source: | Updated: Feb 15, 2016

In the mid 1990s, polycarboxylates(i) in HRWR admixtures were introduced in North America, thus initiating a dramatic paradigm change in our understanding of how to design and use highly workable concrete mixtures. Because of the flexibility, enhanced workability, workability retention with minimal set retardation, and very good finishing characteristics, the acceptance curve for these admixtures was much shorter than anything previously introduced.

Shortly after the introduction of polycarboxylate-based HRWRs, concrete producers began experimenting with SCC in all segments of concrete production; however, nowhere was SCC more rapidly accepted than in the precast market. The ability to fill a mold quickly without vibration, while still maintaining or even improving the plastic and hardened properties of the concrete, made SCC a perfect match for precast concrete producers.

Precasters began using terms like slump flow, viscosity, filling ability, passing ability and rheology to describe this revolutionary type of self-consolidating and non-segregating concrete. Unlike earlier HRWR technologies such as naphthalene (C10H8) and melamine sulfonate (CH3SO2O) condensates, which have fixed-chemistry and limited-performance capability, polycarboxylate technology is highly flexible, meaning that the polycarboxylate polymer can be designed and optimized for a wide range of performance requirements, from high early strength to extended slump life to SCC.

With the emergence of SCC, another class of chemical admixtures – viscosity-modifying admixtures (VMAs) – has been commercialized to address the need for improving the water tolerance and segregation resistance of this highly flowable concrete. The rapid acceptance of VMAs prompted the inclusion of a new admixture category, Type S, in the ASTM C494 standard to assure users that VMAs have no impact on common concrete properties (workability, set, strength and shrinkage).

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