Influence of Coagulation of Polymer Dispersion on the Properties of Polymer-Modified Mortar

Abstract

The coagulation process of polymer dispersion in cement-based materials is different from that of the pure polymer dispersion during drying and film formation. This process is influenced by the various ions released from cement hydration and the interaction between polymer and cement grain in the water. This paper focuses on the coagulation of polymer dispersion during cement hydrating and the influence on the performances e.g. water absorption, flexural and compressive strength and bonding strength of cement mortar. Commercial anionic styrene-acrylate polymer dispersion was investigated in the coagulation process in the polymer-modified cement paste with polymer to cement ratio (p/c) from 5% to 20% and water to cement ratio of 0.3. The amount of coagulated polymer particles was measured by testing the solid content of the supernatant of the diluted polymer-modified cement paste for a period of time. The calorimetric property was measured by TAM AIR calorimeter. Water absorption and mechanical properties of the modified mortar were also measured according to the China standard. The result showed that the polymer dispersion mixing with cement was found to be coagulated in the very early stage under the low polymer to cement ratio, and the quantity of the polymer particles remained in the liquid is quite low within few minutes during this fast coagulation process. The fast coagulation process undermines the influence of polymer dispersion on the cement hydration and the heat evolution. But it has negative impact on the mechanical properties and water resistance. Adding of surfactant into the polymer dispersion extends the coagulation process and improves these performances.