Analysis of superplasticizers used in concrete : HPLC Liquid Chromatography

Organic polymers are largely used in the processing of ceramic powders in order to improve rheological properties. The industry of hydraulic concrete (initially concretes are also powders) currently uses admixtures called superplasticizers, which allow the production of high performance concrete. Altough these admixtures are widely used, their mechanisms of action remain unclear. Measuring the adsorption of these polymers onto the surface of cement particles in aqueous suspensions is usually the first step in related studies. It is often based on a global analysis of the admixture in the aqueous phase, usually by colorimetry or total organic carbon analysis. This traditional approach totally neglects effects linked to molecular mass distribution. In this paper, we show how HPLC is able to high-light the effect of molecular mass distribution on the adsorption of polycarboxylate-polysylphonate polymers. Measurements were performed with two cements having the same chemical composition and the same specific surfaces, but one was ground with and the other without a grinding aid. It is also shown how adsorption changes as a function of cement hydration.