Role of Chemical Bonding on Durability of Epoxy Adhesion to Mortar

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This grant provides funding to investigate the chemical interactions at the interface between epoxy and cement paste or mortar, and the effect of water on those interactions. Based on what is known about the surface chemistry of cement paste, and by analogy with epoxy adhesion to aluminum, we propose that epoxy forms hydrogen bonds with cement paste. In the presence of water, these water-cement paste bonds are displaced by the water molecules, leading to a weakening of the interface. We propose to test this hypothesis through a combination of spectroscopic and mechanical measurements. The surface chemistry of epoxy, cement paste, and mortar will be identified using x-ray photoelectron spectroscopy (XPS) and attenuated total reflection infrared spectroscopy (ATR-IR). Bonding between the two will be identified by placing a thin epoxy coating on the cement paste or mortar and identifying the bonds with XPS and ATR-IR. The role of hydrogen bonds will be quantified by modifying the surfaces to change the surface concentration of hydrogen bonds and by quantitative analysis of the XPS and ATR-IR spectra. The effect of water will be identified using both spectroscopic and mechanical measurements on specimens that have been immersed at 30, 40, 50, or 60 C for up to 12 weeks. Direct tension pull-off tests will be used to measure changes in bond strength as a function of immersion and surface treatment and correlated to the changes in bonding observed with XPS and ATR-IR.This project will provide new insights into the adhesion between epoxy and cement paste and how environmental exposure affects that adhesion and the resulting properties. The primary objective of the project is to provide the fundamental science needed to understand the behavior of these materials when used in real-world applications. The results may be used to develop improved models of aging for lifetime prediction of systems in which epoxy is bonded to cement. It may also provide guidance for developing new materials with improved performance and lifetime.