Polycarboxylate superplasticizers are a type of polymerized water-reducing admixture used to modify the viscosity, plasticity and shrinkage properties of concrete. These admixtures work by steric hindrance resulting from hydrophilic polyether pendent chains grafted on a polyacrylic acid backbone.
Adsorption on cement and its steric effect determines the superplasticizers' dispersion performance, while their adsorption conformation is affected by the length of side chain. The relationship between adsorption of PCE and its dispersion ability was analyzed in various water-to-binder ratio systems.
Synthesis of nonadsorbing PCEs: a new approach to achieve better dispersion and flowability in alkaline cement paste
Researchers recently synthesized polycarboxylate superplasticizers that do not adsorb on cement. This enables more slag or fly ash to be used in the mixture as an alternative to cement, which can help reduce costs.
The synthesis of nonadsorbing PCEs was conducted by using acrylic acid and o-methoxy poly (ethylene glycol) methacrylate ester as starting materials. The polycarboxylates were then synthesized in the presence of a sodium hydroxide solution. The dispersing capability of the nonadsorbing PCEs was evaluated via mini slump tests, which were performed according to DIN EN 1015.
In addition, the dispersion of PCEs was investigated using a pore solution model. The results showed that the adsorption amount of PCEs was proportional to their carboxylate density and molecular mass, while the steric repulsion influenced the adsorption conformation in a significant way.
The results suggest that the adsorption of PCEs on cement varies in a wide range depending on the molecular structure and the steric effect of the side chains. Therefore, the adsorption of PCEs should be adapted to the type and properties of the cementitious system.
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