Effect of redispersible polymer powders on selected mechanical properties of thin-bed cementitious mortars

Abstract

Modern mortars are complex multi-component systems. Among the mortar components, redispersible polymer powders (RDPs) play a unique role. They improve the rheology of fresh mortar while providing flexibility and tensile strength after it has hardened. The impact of polymeric binders on mortar properties has been and is currently the subject of intensive research. This paper describes how the use of different redispersible polymer powders affects cement mortars’ selected properties, i.e., crack bridging ability, adhesion determined by measurement of tensile strength and transverse deformation. Results show that all of the RDPs tested positively affect the properties of the examined system. The most significant increase in the mortar’s tensile adhesion strength was observed for the system with vinyl acetate homopolymer, the lower one for the systems with styrene-acrylic heteropolymers and vinyl acetate and ethylene heteropolymers. All tested redispersible polymer powders in the considered system increase the ability to bridge cracks in cement mortar. However, the smallest increment is observed for the acrylic homopolymer and styrene-butadiene heteropolymer. Other RDPs similarly increase the mortar’s cracks bridging ability under test defined as the ability of the hardened material (mortar) to stop the spread of cracks without damaging it. The results obtained for thin-bed cement mortars in terms of crack bridging ability were evaluated comparing the requirements for water-impermeable products. All examined RDPs showed a similar effect on the transverse deformation value of cement mortar.