Rheological Property,Mechanical Property,and Water Absorption Behavior Of Latex-modified Cementitious Materials

Polymer latex is a commonly used chemical admixture in cement mortar and concrete including tile adhesive,waterproofing mortar,repair mortar,crack-resistant concrete etc.,to achieve various properties.This study systematically investigated the influence rules and the mechanism of the polymer dispersions on the polymer modifeid cementitious systems,paying special attention to the adsorption behavior and the film-forming performance of the polymer particles during cement hydration.The adsorption property of the polymer particles on cement surface and the film-forming properties of the polymer particles were tuned by modification of the surface charge density and the glass transition temperature（T_g）of polymer particles.Rheological properties of fresh cement paste（fcp）,pore structure,mechanical properties,and water absorption of hardened cement paste（hcp）or mortar were investigated in the presence of the polymers.In addition,the water absorption behavior of hydrophobized concrete using silane emulsion was studied.The main findings achieved in this study are as follows:（1）The surface charge density of polymer particles determines their adsorption behavior on the surfaces of cement grains.The influences of polymer particles on cement hydration and rheological properties of the fcp are related to the adsorption behavior.（2）The film-forming property of polymer particles shows a decisive influence on the pore structure of the hcp,i.e.,the addition of polymer with better film-forming property results in a lower open pore volume of the hcp.（3）The addition of polymer reduces the compressive strength and elastic modulus of mortar,and polymer with lower T_g leads to a more significant effect.The influence of polymer on flexural strength and tensile strength of mortar is related to the T_g and content of polymer.The flexural strength and tensile strength of mortar is first increased and then decreased with the increase of the content of low T_gpolymer,and decreased continuously with the increase of the content of high T_g polymer.（4）The addition of polymer reduces the storage modulus of the hcp at the normal temperature（20℃）,and the lower the T_g of polymer particles,the more significant the effect is.The storage modulus of polymer-modified hcp suddenly drops when the test temperature reaches the T_g of polymer.The loss factor of polymer-modified hcp appears the maximum at a temperature slightly higher than T_g of polymer and the maximum loss factor of polymer-modified hcp increases linearly with the increase of polymer content,indicating that the addition of polymer significantly changes the viscoelastic behavior of the hcp.（5）The addition of polymer reduces the initial water absorption rate coefficient（S₁）of mortar,and the polymer with better film-forming performance leads to lower S₁.（6）For the hcps（mortar）containing high T_g polymer,heat treatment promotes the film formation of polymer particles,thus improving their mechanical properties.（7）The incorporation of silane emulsion reduces the water absorption rate coefficient of concrete by decreasing the hydrophilic characteristics of the hcp,but does not change the expansion characteristics of C-S-H during water absorption.Based on this,a method to estimate the long-term water absorption of hydrophobic concrete through short-term water absorption experiments was proposed.The findings of this study have important guiding significance for the development of the polymer dispersion and the application of polymer disperision and silane emulsion in cementitious materials.