This week's post is a review of a technical paper published by "Materials Sciences and Applications" June 2012, titled "Interactions between Superplasticizer and Release Agents at the Concrete/Formwork Interface" by Samir Bouharoun, Yannick Vanhove, Chafika Djelal, Pascale De Caro, Isabelle Dubois.
The efficiency of superplasticizer depends on the quantity of fines, on the quantity of soap formed and so, on the release agent formulation.
The use of superplasticizer ensures that the concrete is fluid enough for easy placement in formworks.
Characteristics of the Materials
Concrete: Two concretes were formulated from an ordinary concrete with different dosages of superplasticizer.
Release Agents: The two release agents selected for this study belong to the two families of oils on the market: one of petrochemical origin, and one of vegetable origin.
Effect of Concrete Formulation on Release Agent behavior
With vegetable-based oil, the interface is organized in two levels:
- The soap film superposed on the oil film
- The layer formed by the soap-oil emulsion
This organization proves to be particularly effective in reducing friction and hydrophobing the wall formwork. Although the superplasticizer interacted less with the mineral oil than with the vegetable oil, its role is equally important in the case of the mineral oil. The superplasticizer stabilizes the interstitial emulsion, which is less rich in soap, thus having a protective effect on the wall formwork that is characteristic of the mode of action of a mineral oil.
Vegetable-based oil retains an advantage over mineral oil, thanks to the double-layer soap-oil organization. The friction of the fresh concrete against the formwork is so reduced more substantially.
Consequently, the performances of superplasticizer depend on the quantity of fines and on the quantity of soap formed. This is why, in order to optimize lubrication performance, the superplasticizer addition rate must be dictated by these two parameters.
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