Nondestructive Inspection Protocol for Reinforced Concrete Barriers

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This document is a technical summary of the unpublished Federal Highway Administration report Nondestructive Inspection Protocol for Reinforced Concrete Barriers, available through the National Technical Information Service at www.ntis.gov.

INTRODUCTION

The National Transportation Safety Board (NTSB) investigation of the accident that occurred on August 10, 2008, on the William Preston Lane, Jr., Memorial Bridge, which crosses the Chesapeake Bay near Annapolis, MD, identified significant corrosion of the anchor bolts attaching the bridge railing to the bridge deck. A subsequent NTSB recommendation stemming from that investigation, H-10-18, was to “expand the research and development of nondestructive evaluation technologies to develop bridge inspection methods that augment visual inspections; offer reliable measurement techniques; and are practical, both in terms of time and cost, for field inspection work; and promote the use of these technologies by bridge owners.” ⁽¹⁾ This document summarizes a response to that recommendation.

Reinforced concrete barriers are generally anchored to the deck of a bridge or retaining wall using reinforcing steel protruding from the main structure or by anchored bars or bolts added during retrofits. Corrosion of steel bars or bolts can weaken this attachment and reduce the capacity of the barrier. The most direct damage resulting from corrosion is the reduction of steel diameter and cross-sectional area. Steel corrosion in concrete is caused primarily by chloride- or carbonation-induced corrosion. Barriers are generally located at or very near the gutter-line of a roadway and may have significant long-term exposure to corrosive deicing materials and other corrosion-inducing environments.

Anchorages and adjacent voids are typically embedded in concrete structural elements and consequently cannot be fully inspected visually. Research has been done on nondestructive evaluation (NDE) methods to evaluate reinforced concrete and embedded steel reinforcement.^(2,3) Four NDE technologies were examined and tested in this project, and the results of those test are reviewed and summarized in this document.