SEM analysis of bond epoxy based layer between hardened concrete and SFRC repairing

Abstract

Thin bonded concrete overlay are commonly used nowadays in repairing concrete structures. Nevertheless, the performance of the structural system (repaired structure) depends on the sound bond behaviour between old and new concretes. Frequently, adhesives based on epoxy resins provide this liaison. In this work the behaviour of three different types of based epoxy adhesives was observed in the bonding of different strength concrete class. Samples for backscattered scanning electron microscopy (BSE) were prepared from extracted pieces - containing the bonding layer - of non reinforced concrete slabs overlaid with thin bonded steel fibre reinforced concrete (SFRC) layer. Different features of each bonding layer epoxy resin type which may explain differentiate mechanical pull-off results as well as failure modes were observed. Micrographs obtained with BSE give clearly bond layer arrangement and minimum and maximum thickness, typical air voids porosity, presence of hydrated cement paste embedded in epoxy layer, mineral admixtures contained in epoxy, and also relevant micro fissures existing in concrete substrate.