Effect of a superplasticizer on the properties of the concrete/oil/formwork interface

The release agents protect the internal surfaces of formwork against corrosion and also ensure easy removal of the concrete elements. On the other hand, the superplasticizers are used to enhance the fluidity of the fresh concrete without adding water, thanks to their surfactant properties. Their contact with release agents can cause interactions near the formwork surfaces during the concrete pouring. The aim of this study is to identify the effect of a polycarboxylic ether superplasticizer on the tribological behavior of fresh concrete at the concrete/oil/formwork interface. Friction tests were performed using a plane/plane tribometer on three concretes with 30% of paste at different dosages of superplasticizer. Moreover, the purpose of the physicochemical study was to clarify the nature of the interactions between concrete pore solutions and release agents. Results showed that the superplasticizer dosage did not have the same effect on the friction according to the oil nature involved at interface. Thus, a description of the processes occurring at the concrete/oil/formwork interface is proposed. When the superplasticizer generates a deflocculating action of the cement particles, it also acts on the stabilization of the soap–oil micellae present at the interface.