NDT evaluation of long-term bond durability of CFRP-structural systems applied to RC highway bridges

Kenneth C Crawford

doi:10.1007/s40091-016-0120-2

Abstract

The long-term durability of CFRP structural systems applied to reinforced-concrete (RC) highway bridges is a function of the system bond behavior over time. The sustained structural load performance of strengthened bridges depends on the carbon fiber-rein- forced polymer (CFRP) laminates remaining 100 % bon- ded to concrete bridge members. Periodic testing of the CFRP-concrete bond condition is necessary to sustain load performance. The objective of this paper is to present a non-destructive testing (NDT) method designed to evaluate the bond condition and long-term durability of CFRP laminate (plate) systems applied to RC highway bridges. Using the impact-echo principle, a mobile mechanical device using light impact hammers moving along the length of a bonded CFRP plate produces unique acoustic frequencies which are a function of existing CFRP plate-concrete bond conditions. The purpose of this method is to test and locate CFRP plates de-bonded from bridge structural members to identify associated deterio- ration in bridge load performance. Laboratory tests of this NDT device on a CFRP plate bonded to concrete with staged voids (de-laminations) produced different frequen- cies for bonded and de-bonded areas of the plate. The spectra (bands) of frequencies obtained in these tests show a correlation to the CFRP-concrete bond condition and identify bonded and de-bonded areas of the plate. The results of these tests indicate that this NDT impact machine, with design improvements, can potentially pro- vide bridge engineers a means to rapidly evaluate long lengths of CFRP laminates applied to multiple highway bridges within a national transportation infrastructure.

Highlights

The load performance of carbon fiber-reinforced polymer (CFRP)-strengthened RC highway bridges is a function of the bond-interface behavior in the CFRP laminate–epoxy–concrete structural system
Bridge owners are faced with two primary questions: (1) how do CFRP structural systems on RC highway bridges perform over extended time (15? years) under the influence of frequent cyclic loading, moisture, and freeze-thaw cycles? (2) How can accurate field data be obtained on CFRP-plate bond condition to evaluate changes in load performance and to establish cost-effective maintenance procedures? This concern is magnified when a national highway system has a large number of strengthened bridges and the load performance of the bridges is critically dependent on the CFRP plate–concrete bond performance, i.e., absence of debonding
The following points can be concluded from the tests presented in this paper: 1. Use of the non-destructive testing (NDT) impact-echo method presented in this paper may be effective in evaluating CFRP laminate bond condition on RC bridge structural members

Summary

Introduction

The load performance of CFRP-strengthened RC highway bridges is a function of the bond-interface behavior in the CFRP laminate–epoxy–concrete structural system. It is necessary to periodically evaluate the bond condition of the CFRP laminates applied to bridges to monitor potential changes (deteriorations) in bridge load performance. A comprehensive CFRP-strengthened bridge inspection and maintenance program with periodic testing and evaluation of the CFRP plate bond condition is necessary to support and sustain long-term bridge performance. CFRP-plate structural systems were applied to multiple bridges on the M2, and two bridges on the M1, to increase bridge load capacity for heavy military vehicle traffic. This FRP application significantly increased the flexural bending moment of bridge structural members. To sustain the designed load performance on this large number of CFRPstrengthened bridges, a reliable field testing procedure in bridge inspection and maintenance is needed to periodically verify bond condition and associated bridge load performance

Objectives

Findings

Discussion

Conclusion