Harold Schultz, Ohio Department of Transportation
As a result of premature failure of some asphalt concrete on a major interstate highway around Columbus, OH, the state legislature required the Ohio Department of Transportation (ODOT) to produce warranty specifications for various items of work. In October 1999, a specification was produced requiring contractors to warrant new bridge decks constructed with high performance concrete (HPC).
Warranty Items
The specification requires contractors to only warrant their workmanship and not the design of the superstructure or the design of the concrete mix. The contractor is required to warrant against alligator or map cracking for a period of one year and against scaling and spalling for seven years. In addition to the requirements of the warranty specification, the contractor is still required to mix and place the concrete as required in our normal specification for HPC. It is still necessary to inspect the placement of the concrete.
Alligator or map cracks are caused when the contractor fails to properly cure the concrete. Due to the small amount of free water in high performance concrete, timely and adequate water curing is very important. While we require wet burlap to be placed immediately after the surface of the concrete has received a broom finish, there are times when the burlap is not placed immediately, the burlap is not wet when it is placed, or the burlap is allowed to dry out before the concrete has cured for the required curing period.
In our experience, scaling has occurred because the contractor added water to the surface of the deck to aid in finishing, or allowed the uncured concrete to freeze during cold weather. Spalling has occurred because the concrete was not properly mixed and the cementitious materials formed into balls. Allowing these balls to be placed in the work in lieu of rejecting the load of concrete can result in spalling.
Review Process
The deck is evaluated three times by a review team. The first evaluation is at one year for alligator and map cracking. At two years, the deck is evaluated for scaling and spalling. The final review takes place one month before the end of the warranty period when the deck is again evaluated for scaling and spalling.
Remedial Actions
If any of the above mentioned defects becomes evident during the warranty period, the contractor is required to make repairs at no cost to the state. The type of repair depends on the severity of the problem.
If alligator or map cracks are found on 20 percent or less of the entire deck area within the warranty period of one year, the contractor is required to seal these cracks with high molecular-weight methacrylate resin. If the area is greater than 20 percent, the contractor is required to remove the top 1 in. (25 mm) from the entire surface of the deck by hydro demolition. This concrete must then be replaced with either a 1-in. (25-mm) thick inlay of latex modified concrete or silica fume modified concrete.
If deck scaling occurs on 20 percent or less of the entire deck area and the depth is greater than 1/8 in. (3 mm) but not greater than 1/4 in. (6 mm), the defective areas are to be ground out. Transverse grooves are then re-established by saw cutting into the surface of the deck and the area is sealed with an approved concrete sealer. If the deck scaling is greater than 1/4 in. (6 mm) deep, the scaled area must be removed to a depth of 1 in. (25 mm). The concrete is then replaced with a 1-in. (25-mm) thick inlay of either latex modified concrete or silica fume modified concrete. The edges of the inlay are to be sealed with high molecularweight methacrylate resin.
If the total area of scaling of the deck exceeds 20 percent of the entire deck surface, the entire top surface must be removed to a depth of 1 in. (25 mm) by the use of hydro demolition. The top surface is then to receive a 1-in. (25-mm) thick inlay of either latex modified concrete or silica fume modified concrete. Similar repairs are required for spalling.
Appeal Process
If the contractor disagrees with the findings of the review team, the contractor may appeal in writing to the district construction engineer. Within 45 days of receiving the contractor’s appeal, the district construction engineer will inform the contractor of the determination. If the contractor does not agree with the determination of the district construction engineer, the contractor may appeal to the central office.
Maintenance Bond
The contractor is required to provide ODOT with a maintenance bond for the bridge deck for a period of seven years. The amount of the bond is 50 percent of the total price bid for the HPC.
Experience
ODOT began providing warranty projects in January 2000. To date, there have been 65 projects bid. There have been 16 decks that have received the one year review. Six of these decks required corrective work for alligator or map cracking.
During the development of these specifications, there was a concern about the impact on the bid price to perform this work. Prior to the development of the warranty specification, the average unit price awarded for HPC was $514/cu yd ($672/cu m) in 1998 and $521/cu yd ($681/cu m) in 1999. During 2000, the first year after the warranty specification was developed, the average unit price awarded for high performance concrete with warranty was $553/cu yd ($723/cu m). In the following year, the average price awarded for HPC with warranty dropped to $514/cu yd ($672/cu m).
More Information
Details of the specification are available at www.dot.state.oh.us and select warranty program info from the ODOT option menu or contact the author at 614-644-6628.