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23 a 6% discount rate, hot rubberized asphalt membrane was the cost of retrofit epoxy-coated reinforcement, Iowa system the sixth-lowest-cost strategy. The analysis was based on a overlays, Kansas system overlays, and membrane overlays. service life of 75 years and assumed that the top 40 mm (1.6 She concluded that the membrane overlays, with an average in.) of the asphalt overlay was replaced at 20 and 60 years cost of $0.12/ft2/year of service life based on 1979 dollars, and the membrane and asphalt overlay replaced at 40 years. were the most cost-effective rehabilitation technique. Hearn and Xi (22) evaluated the relative costs of the follow- Liang et al. (23) reported that preformed sheet membranes ing four types of protection of reinforcement in bridge decks: with asphalt overlays have been used in Colorado. Hot rub- berized asphalt membranes and spray-applied liquid mem- Uncoated reinforcing bars with rigid overlay, branes are less expensive than preformed sheet membranes. Epoxy-coated reinforcing bars and a concrete surface sealer, In the survey for this synthesis, agencies were asked Uncoated reinforcing bars protected with a waterproof- to provide unit costs for labor, equipment, and materials ing membrane and bituminous overlay, and for waterproofing membranes systems used on new and Epoxy-coated reinforcing bars protected with a water- existing bridge decks. The reported data showed a wide proofing membrane and bituminous overlay. variation of costs within each state and between states. In the United States, reported bid prices ranged for $0.56 to The history of 82 bridge decks built between 1969 and $42.80/ft2. In Canada, reported costs ranged from C$1.69 1991 was used to estimate the service life and to generate to C$8.55/ft2. population models of service life. Costs were computed as present value, discounted annualized cost, and annual- ized cost without discount factors. Discount factors rang- REPAIRS ing from 2% to 10% were used. By all present value and annualized cost measures, decks with waterproofing mem- In the survey for this synthesis, agencies were asked if they branes were the least expensive. This conclusion was not had requirements or specifications for repair of membrane sensitive to the value of the discount factor but was influ- systems. Most respondents who answered this question indi- enced in part by the longer service life predicted for bridge cated that they do not repair damaged membranes but would decks with membranes. replace a part or all of the system depending on the sever- ity of the damage. Any damage caused before the asphalt Distlehorst (20 ) provided estimates of relative annual overlay was placed would be repaired per the manufacturer's costs of bridge deck overlays used in Kansas. She compared recommendations.