The influence of low-dosage styrene-acrylate dispersions on mortar strength

Polymer-modified mortars (PMMs) are widely used as dry-mix mortars, such as cementitious tile adhesives. Rational design of polymer-modified mortars requires detailed insight into the interplay between polymer and cement phases. Systematic data covering diverse polymer chemistries, concentrations, and cement compositions can substantially advance mechanistic understanding and material optimization. The main objective of this study is the investigation of mortars containing a low-dose (i.e., 2 wt%) of 13 different styrene-acrylate emulsion polymers. We report data on the polymer-modified mortar’s rheology, strength (1, 7, and 28 days), hydration kinetics via isothermal heat flow calorimetry, and stiffness evolution via ultrasonic pulse velocity measurements. Furthermore, we compare the influence of the polymers on mortar strength evolution by a) evaluating the relative deviation of the mortars from a linear regression to the relationship between strength and density for polymer-free reference samples, and b) by ensuring similar mortar densities through the use of a defoamer to avoid air-entrainment. With few exceptions, we observe a small reduction in compressive and bending strength at all ages for the PMMs. The influence of the polymers on the rheology is noticeable but of small magnitude. Finally, all polymer emulsions exhibit a slight retarding effect on the main hydration reaction of Portland cement. In summary, the study provides extensive data on the effect of common styrene-acrylate dispersions on mortars at the low end of commonly employed polymer dosages.