Title: Impact-Echo Studies of Interfacial Bond Quality in Concrete: Part l-Effects of Unbonded Fraction of Area

Author(s): Jiunn-Ming Lin and Mary Sansalone

Publication: Materials Journal

Volume: 93

Issue: 3

Appears on pages(s): 223-232

Keywords: bond (concrete to concrete); concretes; impact tests; nonde-structive tests; tensile strength.

DOI: 10.14359/9806

Date: 5/1/1996

Abstract:
This paper is the first of two papers that summarize results from a research project on the feasibility of using the impact-echo method to determine inter-facial bond quality in layered structures such as overlaid concrete slabs or repaired concrete structures. For purposes of this study, interfacial bond quality is based on unbondedfraction (ratio of unbonded area to total area) and bond tensile strength. This paper focuses on demonstrating how the unbonded fraction at an interface affects impact-echo response. Results obtained from numerical (finite element), experimental, and field studies for concrete structures with concrete overlays or repairs and concrete slabs with asphaltic concrete overlays are presented. Results show that very small unbonded fractions at an interface do not significantly affect impact-echo response. As unbonded fraction increases, a shift in the solid structure’s thickness frequency occurs and a small amplitude peak corresponding to reflections from the interface becomes discernible. As the unbonded fraction becomes large, the shift in the thickness frequency becomes more pronounced, and a distinct, larger amplitude peak corresponding to rejections from the interface becomes apparent. Eventually, the response resembles that of a crack at the interface.