Characterization of Polycarboxylate-Ether Based Superplasticizer on Cement Clinker Surfaces

The application of Ordinary Portland Cement (OPC) based binder is commonly improved by the addition of rheology modifying agents, i.e. superplasticizers. In this work the interaction between polycarboxylate-ether based superplasticizers (PCEs) and the hydration products formed in aqueous solutions, after 30 min on polished OPC clinker surfaces is studied. Energy-dispersive X-ray spectroscopy provides the chemical analysis and the localization of the different phases below the superficial hydration products. Time-of-flight secondary ion mass spectrometry allowed to detect for the first time on which cement phases PCE preferentially adsorbed, and is used to map the distribution of the chemical elements at the surface of the clinker. Force measurements in liquid, performed by atomic force microscopy (AFM) with sharp tips, test the surface-tip interactions in presence/absence of PCE. The results show that superplasticizers interact strongly with K+ and SO42- ions, precipitating in K2SO4 salts. When PCE traps the sulfate ions, the concentration of this ions specie in the solution is reduced, inhibiting ettringite formation. AFM force measurements allow the distinction between positively and negatively charged hydration products, revealing that the interaction forces between different phases are homogenized by the presence of PCE, providing stability to the suspended particles.