Aug. 16, 2021
About 20 years ago, a new superplasticizer based on polycarboxylate polymers (PCE) was introduced commercially to the North American concrete construction industry. Just as the use of naphthalene-based admixtures significantly improved numerous engineering properties of plastic and hardened concrete beginning in the 1970s, polycarboxylates have further expanded the performance of concrete mixtures.
Essentially all polycarboxylate-based mixtures are formulated with defoamers to control the unwanted air entrapment inherent in PCE polymers. For aerated and non-aerated concrete applications, air content can often be effectively managed by selecting a PCE-based high efficiency water reducing agent product that is most compatible with the work material. In general, PCE-based products can make aerated admixtures (AEAs) more effective.
Unlike PNS superplasticizers, PCE polymers can be readily and irreversibly adsorbed by certain clay fines that may be present in various aggregate sources. When clay is present in certain sands, PCE is expected to be used at 50% higher rates than PNS. Therefore, if the amount of PCE water reducing agent is unexpectedly increased, the clay fines in the total supply should be checked as a priority.
Again, unlike PNS-based high efficiency water reducing agents, which should always be added in a delayed addition mode (i.e. after the cement and water have started to mix), PCE is relatively insensitive to addition time and therefore offers greater flexibility in the concrete batching process.
When PCE-based superplasticizers were used in combination with set promoters and corrosion inhibitors containing calcium salts, an unexpected increase in strength was observed compared to similar concrete mixtures incorporating PNS-based products. This synergistic effect with the increased strength of PCE was first observed in mixtures containing calcium nitrite based corrosion inhibitors.
PCE superplasticizers replace PNS/lignin and Type A water-reducing products at a dose rate of about one-third. Also note that the AEA dose rate is reduced by 50% when using PCE admixtures for concrete to obtain the same air content.
In summary, while the concrete industry has learned much about the versatility and limitations of utilizing PCE-based water reducing agents, chemists, in collaboration with concrete technicians, will continue to modify polymer structures to achieve new capabilities in concrete mixes for production, placement and longevity. Please contact SANCOLO to get more information about chemical products.