Correlation between Ultrasonic and Static Mechanical Properties during Curing of Cold-Curing Epoxy Adhesives

Ultrasonic wave propagation has been used to monitor the progress of the curing reactions of an epoxy adhesive employed in civil engineering applications. Ultrasonic velocity and attenuation have been measured in isothermal conditions on the neat resin, as well as in a coupled concrete-resin-concrete system. The evolution of ultrasonic properties has been correlated with the dramatic increase of mechanical properties changing from those of viscous liquid to a glassy polymer. The change of velocity during cure has been used as a measure of the progress of the reaction in order to have a precise indication of the hardening of the adhesive. Correlation charts between static and dynamic properties have been produced both for the neat resin and for the multi-layer system. Such correlation charts, developed for a given epoxy system, can be considered as a powerful tool to measure the progress of curing reactions and, in turn, the development of mechanical and adhesive strength of the bonded structure.