Model of the charged mosaic surface of the cement particle based on the adsorption behavior of surfactants using ATR-FTIR spectroscopy

Abstract

A charged mosaic structure is often introduced to explain the adsorption behavior of ionic additives in cementitious materials, no matter whether the apparent zeta potential of the solid phase is positive or negative. However, an in-depth model of this mosaic structure has not been developed. In this study, the difference spectra of selected cationic, anionic and nonionic surfactants adsorbing onto cement particles were investigated using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. For concentration-resolved ATR-FTIR spectra by adding cement particles to surfactant solutions, and for time-resolved ATR-FTIR spectra by adding cement particles to the anionic surfactant/Ca(OH)2 mixtures, specific features appear at ~2920 and ~2850 cm−1. If these bands are positive, it indicates that an ordered structure of the surfactant alkyl tail is formed, and if these bands are negative, a disordered structure is formed. Therefore, to explain the adsorption process, a charged mosaic surface model of the cement particle is developed. The results indicate that the heterogeneously charged mosaic surface consists of negatively charged parts which have higher charge density and are relatively isolated, and positively charged parts which have lower charge density and are relatively continuous. This structure arises from the distribution of hydrate phases with different electrical properties.