Drying shrinkage reduction of polymer modified mortars using redispersible polymer powder by use of shrinkage reducing agents
Kim Wanki; Ohama Yoshihiko; Demura Katsunori
Abstract:In general, the drying shrinkage of polymer-modified mortars using redispersible polymer powders is much higher than that of unmodified mortar. The purpose of this study is to develop effective powdered shrinkage-reducing agents for reducing the drying shrinkage of polymer-modified mortars using a redispersible poly (ethylene vinyl acetate) (EVA) powder, which is widely used for the manufacture of premixed type polymer modified mortar products at present. Polymer-modified mortars using the redispersible EVA powder with three powdered shrinkage-reducing agents were prepared with various polymer-cement ratios and shrinkage reducing agent contents, and tested for drying shrinkage and strength. The conclusions obtained from the test results are summarized as follows: (1) The drying shrinkage of the redispersible EVA powder modified mortars with a powdered shrinkage-reducing agent, polyethylene glycol with a molecular weight of 3000 is remarkably reduced with increasing shrinkage-reducing agent content, and becomes approximately a half of that of the redispersible EVA powder modified mortars with the same polymer cement ratios and without the shrinkage reducing agent at a shrinkage-reducing agent content of 6%, (2) The drying shrinkage of the redispersible EVA powder modified mortars with the polyethylene glycol can be predicted as a function of the shrinkage-reducing agent content, polymer-cement ratio, water cement ratio, air content and surface tension (of polymer modified paste extracts), and (3) The addition of the polyethylene glycol to the redispersible EVA powder-modified mortars causes a reduction of 28% or less in the flexural strength and a reduction of 20% or less in the compressive strength. Key Words:polymer-modified mortars, redispersible polymer powder, shrinkage-reducing agents, drying shrinkage reduction, strengths