Field Evaluation of Reinforced Concrete Repairs Using Hydrodemolition, Galvanic Cathodic Protection, or Impressed Current Cathodic Protection

About the report:

For the Virginia Department of Transportation (VDOT), substructure repairs are costly, and the durability is a concern. Current conventional concrete removal methods commonly use chipping hammers and shotcrete or self-consolidating concrete (SCC), plus discrete galvanic point (DGP) anodes, for such repairs. The types of concrete VDOT uses in these repairs are resistant to chloride ion infiltration because of low permeability, which their high-resistivity values indicate. When DGP anodes are used in patch repairs, lower resistivity concretes with higher permeability are recommended to facilitate ionic current flow.

To facilitate the placement, aesthetics, and longevity of these types of repairs, SCCs were introduced. For longevity, two approaches were explored. One approach was large-area concrete removal through hydrodemolition and placing SCC. The other approach was to leave some of the chloride-contaminated areas in their current condition and apply a cathodic protection (CP) system for the whole element.

Researchers anticipated that these modifications would provide VDOT with comparisons against the current practice of using shotcrete or SCC, chipping hammers, and DGP anodes. In general, low-permeability SCC replaced inferior quality concrete in areas where it was removed. The only exception was that a lower resistivity concrete was used to ensure better current flow where ribbon anodes were placed. The following lists the four substructure rehabilitation techniques investigated based on the two aforementioned approaches.

1. Hydrodemolition to remove delaminated concrete and replace it with SCC.
2. Conventional removal of delaminated concrete, replacement with SCC designed for CP, and the installation of a CP system on each structure. The CP systems included two different impressed current CP systems and one galvanic current CP system. Each CP system required a remote monitoring unit that could be observed at the district, central office, and Virginia Transportation Research Council (VTRC), plus technical support.
3. Conventional removal of delaminated concrete, placement of precast anodes in the perimeter of the removed concrete, and replacement of the removed concrete with SCC.
4. Conventional removal of delaminated concrete, placement of precast anodes in the perimeter of the removed concrete, and replacement of the removed concrete with routinely used shotcrete.

All repairs and tasks were completed successfully. This report includes a parallel effort that is documented in a technical assistance report. This work showed that DGP anodes have limited benefits because they protect a limited area around the perimeter. Furthermore, this protection lasts only a few years because the areas farther away from the patch continue to deteriorate and soon require new repairs. It is recommended VDOT consider using large-area deteriorated concrete removal by hydrodemolition rather than small-area patches without any DGP anodes, or install a CP system for the whole element if some of the chloride-contaminated concrete remains.

Supplemental materials can be found at https://library.vdot.virginia.gov/vtrc/supplements

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