Publication Number: FHWA-RD-99-108
Date: October 1999

Tech Briefs Report on Partial Depth Spall Repair and Galvanic Cathodic Protection

Two new Tech Briefs summarizing recently concluded Federal Highway Administration research projects will be available this fall. Each brief reports the key findings of the research and details how these findings will affect current practices.

Portland Cement Concrete (PCC) Partial-Depth Spall Repair (Publication No. FHWA-RD-99-77) describes the results of a 7-year study sponsored by the Strategic Highway Research Program (SHRP) and FHWA. The study examined the merits and deficiencies of various materials and practices for repairing spalling, which is the cracking, breaking, chipping, or fraying of PCC slab edges at joints and cracks. Common in jointed concrete pavements, spalling can affect just a few millimeters of the concrete slab, or extend the full depth of the slab. Because most spalls are repaired before they extend below the top third of the slab, the repairs are often referred to as "partial depth" ones.

The Tech Brief summarizes the study, which evaluated more than 1,600 partial-depth patches on four highways in different regions of the country. As a result of the study, the LTPP program recommends using a chip-and-patch procedure rather than a saw-and-patch procedure when performing maintenance work.

The second new Tech Brief, Galvanic Cathodic Protection of Reinforced Concrete Bridge Members Using Sacrificial Anodes Attached by Conductive Adhesives (Publication No. FHWA-RD-99-113), describes the development and testing of a zinc anode/hydrogel for use in galvanic cathodic protection of reinforced concrete bridges. Although cathodic protection has proven to be an effective technique for protecting reinforced concrete bridge decks and substructures from corrosion caused by deicing salts or seawater, some installations have experienced problems. Most of these problems have been caused by improper maintenance on the complex impressed-current cathodic protection systems that are typically used. Although galvanic cathodic protection systems are simpler and require less maintenance, the anodes often do not provide enough current.

The study described in the Tech Brief was aimed at developing and testing anodes and conductive adhesives that could provide sufficient current to protect reinforced concrete structures and help reduce corrosion. The zinc anode/hydrogel conductive system that showed the most promise was installed on three bridges in Florida and Oregon and monitored over 3 years. The study found that the zinc anode/hydrogel system was easy to install and provided adequate protective current flow, although more field experience is needed to determine the anodes' long-term performance.

For more information on the PCC partial-depth study, contact Monte Symons at FHWA, 202-493-3144 (fax: 202-493-3161; email: monte.symons@fhwa.dot.gov). For more information on the cathodic protection study, contact Y. Paul Virmani at FHWA, 202-493-3052 (fax: 202-493-3442; email: paul.virmani@fhwa.dot.gov). The Tech Briefs are scheduled to be available next month. To order the PCC Tech Brief, contact LTPP Customer support services at 423-481-2967 (email: ltppinfo@fhwa.dot.gov). To order the cathodic protection Tech Brief, contact the FHWA Report Center at 301-577-0906 (fax: 301-577-1421).

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