Shrinkage of latex-modified

Kawanol found that, compared to ordinary cement mortar, a reduction in the drying shrinkage of latex-modified mortars is mainly due to the effects of the surfactants and antifoamers contained in the latexes. 

Figure 4.34 Twenty-eight-day drying shrinkage of latex-modified mortars.

As seen in the Fig. 4.4,t l the water-cement ratio of latex-modified concrete at a given slump is markedly reduced with an increase in the polymer-cement ratio. This water reduction effect is found to contribute to strength development and a drying shrinkage reduction. 

Figure 4.39 Steel fiber content and polymer-cement ratio vs. 84-day drying shrinkage of steel fiber reinforced latex-modified mortars.

Hot weather causes rapid drying of the latex-modified concrete, which makes finishing difficult and promotes shrinkage cracking. Placing overlays at night avoid these problems. 

This paper discusses the properties of polymer-modified mortars with silica fume. The polymer-modified mortars using a styrene-butadiene rubber latex and an ethylene-vinyl acetate emulsion are prepared with various polymer-cement ratios and silica fume contents, and tested for flexural and compressive strengths, adhesion, water absorption and permeation, water resistance, drying shrinkage, carbonation and chloride ion penetration. The effects of the polymer-cement ratio and silica fume content on the properties of the polymer-modified mortars are e>amined. In conclusion, the addition of the silica fume causes improvements i- the compressive strength, resistance to water permeation and chloride ion penetration. However, the adhesion, resistance to water absorption and carbonation and drying shrinkage are not improved by silica fume addition. 

A modified type of natural mbber which has many processing advantages over normal sheet and crepe rubbers. It shows reduced shrinkage, reduced die swell and much better retention of dimensions especially in complicated extrusions. It is made by adding a quantity of vulcanised latex to normal latex before coagulating. See PA 80. 

Polymer-modified mortars can be obtained by replacing part of the mixing water with a synthetic latex (e. g. styrene butadiene or acrylate) to the mix. Although the binder is still cementitious, and thus alkalinity is guaranteed, the latex may improve the workability, the waterproofness, the carbonation and chloride resistance, the tensile and flexural strength of the repair mortar [8]. It can also reduce the modulus of elasticity, increase the bond to the substrate, reduce the rate of drying out and thus the rate of shrinkage. 

---