Investigation of the effect of waterborne epoxy resins on the hydration kinetics and performance of cement blends

Abstract The hydration process and products of polymer-modified cement determine its pore structure and mechanical properties. However, relatively few studies have systematically studied the hydration behavior, microstructure and mechanical properties of waterborne epoxy resin (WER)-modified cement blends. This study aims to investigate the influence of the WER content and curing temperature on the early hydration process and hydration product evolution of cement paste. Moreover, the retardation effect of WER during cement hydration on the microstructure and mechanical properties of cement mortar was also studied. In this investigation, three WER contents in the emulsion (i.e., 3%, 6% and 9%) and two curing temperatures (i.e., 20 °C and 40 °C) were employed. The hydration behavior of WER-modified cement over 72 h was characterized by means of the hydration heat, and the hydration kinetics were calculated by using a model proposed by Krstulovic and Dabic. The hydration process of the modified cement paste was characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric (TG) analysis, and scanning electron microscopy (SEM). The microstructure, pore structure, compressive strength and flexural strength of the modified cement mortar were also investigated. The results showed that the WER-modified cements exhibited a lower hydration rate in the acceleration period and released less hydration heat than the plain cement. The retardation effect of WER was mainly related to the prolonged interactions at phase boundaries (I process). The higher the WER content was, the more significant the retardation effect. As the WER content increased, a decreasing content of CH at various curing ages in the modified cement paste was observed according to the FTIR spectroscopy, XRD, and TG analysis results. However, when the curing temperature was increased from 20 °C to 40 °C, the hydration rate during the acceleration period notably increased, and the CH content also increased, suggesting an increase in the hydration degree. The compressive strength of WER-modified cement mortar decreased as the WER content increased, which may be related to the cement having a lower hydration degree. The use of an optimum WER content (3%) refined the pore structure in the cement mortar, which resulted in an increase in its flexural strength.