Field Comparison of the Installation and Cost of Placement of Epoxy-coated and MMFX 2 Steel Deck Reinforcement: Establishing a Baseline for Future Deck Monitoring

About the report:

As part of the Innovative Bridge Research and Construction Program (IBRCP), this study was conducted to use the full-scale construction project of the Route 123 Bridge over the Occoquan River in Northern Virginia to identify and compare any differences in the installation practices and comprehensive placement costs of epoxy-coated reinforcing steel (ECR) and MMFX2. The study also established a baseline of the condition of the bridge upon completion of construction and initial maintenance.

During construction, two separate bridge decks were built, and a raised median was used to cover the longitudinal joint between the two decks. The southbound deck was built using ECR, and the northbound deck was built using corrosion-resistant reinforcing steel (CRR), which in this case was MMFX 2. To construct the two decks required 576,823 lb of ECR and 674,447lb of MMFX 2. The concrete strength reached 100% of the design strength within 4 days for the northbound deck. The average thickness of the decks was 8.76 in for the southbound deck and 9.15 in for the northbound deck. Stay-in-place forms were used to construct Spans D through G for both decks; Spans A through C were constructed using formwork that was removed to expose the underside of the decks.

Upon completion of construction, an in-depth survey of both decks was conducted. Cracks were present on both decks, and a recent visual analysis of the underside of the decks indicated that moisture is able to penetrate to the bottom of the concrete. Half-cell potential measurements indicated most of the MMFX 2 had reached a passive condition, which presently indicates an insignificant corrosion rate. Resistivity measurements on the northbound deck indicated that if the steel were to become active, it has a low probability of significant corrosion. Chloride analysis indicated salt is penetrating the upper region of the concrete, but the regions closer to the steel have a lower chloride concentration. Based on these findings, the two decks should allow a fair comparison of corrosion susceptibility for the two types of reinforcing steel used.

Inclusion of the labor cost to place ECR in the southbound deck and unanticipated direct costs raised the in-place unit cost of ECR from $0.51/lb. to $0.90/lb. Inclusion of the labor cost to place MMFX 2 in the northbound deck raised the in-place unit cost of MMFX 2 from $0.78/lb. to $0.87/lb. The cracks in the ECR side were sealed as part of the original construction. By including the indirect labor costs to VDOT and road user costs to the public imposed by a crack sealing operation on the southbound deck, the comprehensive in-place cost of ECR more than quadrupled its unit bid price to a final in-place cost range of $2.34/lb. to $2.90/lb., making ECR much less cost-effective in retrospect than it appeared to be at the planning stage of the project. This hidden cost increase for ECR supports the recent decision by VDOT to pursue CRR rather than ECR for future construction and highlights the need to consider at least direct sealing costs when comparing ECR with CRR.

The study recommends that VDOT’s Structure & Bridge Division (1) continue the implementation of the recently approved CRR specification, and (2) be attentive to the possibility that polymer-coated steel bars may be costlier per unit than uncoated bars for reasons of special handling and transport requirements as well as unanticipated preventive maintenance. Further, the Virginia Transportation Research Council should monitor the Route 123 Bridge periodically to assess the relative conditions of the ECR and MMFX 2 reinforcement over time.

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