Effects of Vinyl Acetate-Ethylene Emulsion on Setting Time and Mechanical Properties of Alkali-Activated Cementitious Materials

摘要

This paper studies the effects of VAE emulsion (vinyl acetate-ethylene emulsion, containing 70 to 95% vinyl acetate) on the setting time and mechanical properties of sodium metasilicate-activated slag-fly ash cementitious materials. Sodium metasilicate is used as an activator, and the alkali equivalent (mass percentage of Na_2O provided by sodium metasilicate in the cementitious material) is 8%. The content of fixed fly ash, fine slag powder, and Na_2Si_3 is 30, 54.26, and 15.74 wt.%, respectively. VAE emulsion is mixed with polymer-cement ratios (mass ratio of emulsion to cementitious material) of 2.5, 5, 7.5, and 10%. The water content in the emulsion is subtracted during the mixing and measuring. In the experiment, the emulsion and the activator are stirred well before they are mixed with the powder. Research shows that C-S-H gel is the main hydration product of sodium metasilicate-acti-vated cementitious material and adding VAE emulsion does not produce new crystal hydration products. When the VAE emulsion content is higher than 5%, some unreacted polymer particles in the slurry exists, which can improve the toughness of the mortar and prolong the setting time of the cementitious material. However, the compressive strength of the mortar decreases and the dry shrinkage rate increases. The results of hydration heat and ion dissolution experiments show that with polymer coated on the surface of sodium metasilicate particles, the dissolution rate is reduced, and the hydration heat release of the cementitious material is slowed down. In addition, the dissolution rate and dissolution amount of sodium metasilicate are reduced, which increases the setting time of the cementitious material.