Early-age bond performance in FRP-concrete system and the need for additional test protocol (original) (raw)

25th Australasian Conference on Mechanics of Structures and Materials (ACMSM25), Brisbane, Australia, 2018

Abstract

This study presents new observations about early-age FRP-concrete bond behaviour under hygrothermal conditions whose details have been omitted in previous works in the area. Several accelerated laboratory conditioned double shear bond tests were conducted on FRP-concrete specimens using two different concrete mixtures for a period of 5 weeks. For the concrete and adhesive materials used, the selected exposure period yields results with little decrease to even increase in the bond capacity contrary to the anticipated immediate bond degradation. In addition to the FRP-concrete double shear bond tests, the work includes two more experiments, one for the epoxy dumbbells and the other for the FRP coupons in order to provide more legitimate basis for the conclusions against the commonly adopted approaches reported in the literature. The study identifies two regimes defining the bond behavior as the exposure period or temperature increases: strength-gain and strength-deterioration regimes. Whether or not moisture and/or temperature deteriorates the FRP-concrete bond, depends on the threshold point delineating the two defined regimes. The threshold point, itself, depends on the epoxy glass transition temperature, concrete material and behaviour as well as deterioration rates of epoxy cohesion and that of its interfaces with the other adherends. Some recommendations on the need for assessment, in form of additional test protocol, to establish the minimum exposure and temperature level needed to capture the approximate instant for initiation of the FRP-concrete bond degradation.

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