Optimal preparation and degradation characterization of repair mortar containing waterborne epoxy resin emulsions

• An optimal mixture of waterborne epoxy resin cement repair mortar including coalescing agent was obtained based on a multi-factor analysis. • Degradation processes under the effects of water immersion, thermal ageing and hydro-thermal ageing were characterized. • Reversible and irreversible changes were found in different ageing tests. • Raman spectroscopy was adopted to analyze the degradation mechanism. An orthogonal experimental investigation was conducted to optimize preparation parameters of repair mortar containing waterborne epoxy resin and the degradation performances under three types of ageing were evaluated: (Ⅰ) water immersion, (Ⅱ) thermal ageing, and (III) hydro-thermal ageing. Raman spectroscopy was adopted to characterize phase changes and chemistry evolution during ageing tests. The results indicated that water-cement ratio had a significant influence on compressive and flexural strength. Meanwhile, polymer-cement ratio distinctly influenced bonding strength and flexural strength. When the dosage of coalescing agent was chosen at 5%, crest points were observed for all the properties. The optimal combination was obtained by a comprehensive comparison and the corresponding flexural strength, compressive strength and bonding strength had the balanced values of 10.9 MPa, 55.2 MPa, and 7.3 MPa, respectively. Reversible decreases of residual coefficients were found under water immersion condition while the changes under thermal ageing were almost irreversible. The residual coefficients under coupled effects of humidity and thermal (hydro-thermal ageing) exhibited more complication than that of single factor. The Raman peak related to AFm/AFt along with the broad oxidation or hydrolysis bands was observed, which could provide an explanation for irreversible decline in mechanical strength in the ageing tests.