Influence of low fractions of styrene/butyl acrylate polymer latexes on some properties of ordinary Portland cement mortars

The influence of the chemical structure of styrene/butyl acrylate latexes on some properties of ordinary Portland cement mortars has been investigated for low fractions of polymer with respect to the amount of cement. The structural parameters that were varied included the presence of carboxylic surface changes, the nature of the surfactant system, the molecular weight of the non-ionic emulsifier, and the particle surface coverage. The first part of the study showed that sterically stabilised latexes remain colloidally and chemical stable for several hours in the cement interstitial medium. Moreover, no interaction could be shown between cement and latex components. Then, for a fraction of about 5wt.-% of polymer, no significant influence of the presence of the latex was observed on the end use properties of the mortars. However, it clearly appears that the use of a fraction anionic stabiliser is highly detrimental to the paste the workability, whereas this latter property is improved by the presence of non-ionic surfactant due to steric repulsion forces. Finally, the microstructure analysis confirms that the particles are homogenously dispersed in the mineral matrix and they remain smooth and spherical.