Determining Economic Strategies for Repair and Replacement of Low Slump Overlays of Bridge Decks

Project summary:

Hundreds of bridge decks in Minnesota were reconstructed with low slump overlays between 1974 and 1981. The 3.3 million square feet of bridge deck associated with these bridges is nearing the end of its service life. Assuming a $40 per square foot unit cost to reconstruct these decks, the resulting construction costs exceed $130 million. The purpose of this project was to generate strategies that MnDOT can use to make decisions regarding this set of bridges. As these bridges continue to age, MnDOT will need to make choices between (a) no intervention, (b) overlay repair, (c) overlay replacement, and (d) deck replacement.

In the interest of providing tools for the cost-effective maintenance of an aging inventory of bridges, a method for comparing feasible repair/replacement sequences for low-slump concrete overlays for bridge decks was developed. The method relies on a technique for computing deterioration curves using inspection data from the National Bridge Inventory. Over twenty years of inspection data for bridge decks in Minnesota, which were overlaid with low-slump concrete overlays placed between 1974 and 1981, was used. The deterioration curves were assumed dependent on several material and geometric variables identified by means of a literature review, and the statistical significance of these parameters on deterioration rates was examined. These variables include span length, average daily traffic, and superstructure material type, and piecewise linear deterioration curves were constructed for various subgroups with similar deterioration characteristics. Present value cost analysis was used to price the available options by identifying the sequence of repairs that has the least cost while maintaining a specified performance measure. The present value analysis considers the costs and timing of repair/replacement sequences, inflation, and the discount rate.

This project was prepared in response to MnDOT FY04 Problem Statement 120, and it is aligned with MnDOT Performance Measure Categories 1.2 (Physical Condition of the Infrastructure) and 8.3 (Cost Effective Administration).