6533b834fe1ef96bd129d213

RESEARCH PRODUCT

Influence of superplasticizers structure on the hydration, the initial surface creation and the fluidity of cement model systems

subject

description

Nowadays the use of superplasticizers admixtures becomes unavoidable for concrete. It allows enhancing the rheological properties at the fresh state: the initial flow and slump retention during the 2-3 first hours of the life of a concrete. The understanding of this mechanism is still partly elucidated for PCE (grafted copolymers). The aim of this thesis was to challenge the assumption of the evolution of the adsorbed amount of PCE per instantaneous mineral surface unit as origin of the fluidity temporal evolution during the workability period.On an inert system (calcite), we confirmed that the fluidity is mainly governed by the adsorption level. Thus for a same surface adsorption density, the fluidity of the paste is roughly similar whatever the structure of the PCE. On an inert system also (calcite or ettringite), the modification of the anionic function provides a technological way to improve the resistance of the adsorption against the variation of the sulfate ions concentration.The surface area of a reactive model system (tricalcium aluminate, gypsum, hemihydrate and calcite) has been measured by two techniques during the workability period: the N2 adsorption (BET) and the water proton relaxometry (RMN). The PCE adsorption per surface unit has been calculated and analysed in link with the fluidity of the paste. In that case, the simple relation, shown on the inert system, is not verified because the presence of PCE has also an impact on the hydration and on the extent of the surface area. Especially PCE lead to increase the surface by changing the morphology of ettringite. The specific surface area of ettringite increases when the grafting density of PCE decreases.