Mastering Flow Loss in Superplasticized Cementitious Systems
S. Mantellato; Q. Mehmeti; L. Ceni; M. Palacios; and R.J. Flatt
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One of the essential problems of superplasticized concrete is the loss of fluidity over time. To limit this problem one must improve the compatibility of superplasticizers and cement. This is not a trivial task as cement contains phases with different responses to superplasticizers in the first hours of hydration.
In the present work, the role of the polymer structure on the flow loss over time on superplasticized cement pastes has been studied. For this, we have correlated the impact of different molecular structures on the adsorption degree and ionic solution composition with the rheological properties of fresh cement pastes. The results revealed a high excess of aluminium in the aqueous solution. This could be due to aluminum complexation by the polymer or a poisoning of ettringite growth complemented by a stabilization of nano-sized ettringite particles. In addition, except for one of the studied polymers, the flow loss seems to decrease abruptly when the concentration of carboxylate ions in solution drops below a critical value (0.7-1.2 µeq/g).