March 12, 2012 Bridge Preservation Webinar
Bridge Preservation presenters’ responses to webinar questions
- Adam, what is your best most cost effective preservation method for (1) thermal and minor settlement cracks (2) joints or lateral separation between wingwalls/abutments & superstructure
For minor cracks in any location except the decks we generally have been using injected epoxy to seal them. We’ve used this for bridge abutments, wing walls and concrete culverts. Of course if the crack is more serious in nature we investigate and address the cause before repairing any cracks. Epoxy injection has limits on the width of the crack that can be repaired, but for minor cracks it has been effective.
- What detailing measures are taken for the link slab to not crack at the joint locations?
We use four techniques to minimize cracking in the "link slabs":
- Provide a bond–breaker between the tops of the adjacent beams and the bottom of the concrete.
- Remove any studs from the top of the beam to eliminate mechanical engagement between the beam and the link slab.
- Saw a ½" notch at the top of the joint between the link slab and the existing deck and fill with EP–2 or silicone.
- Require that the existing longitudinal deck reinforcement extend into the link slab. Splice that deck reinforcement with the longitudinal reinforcement in the link slab.
Why FHWA still has the 80 Sufficiency rating is minimum to be eligible for HBP funds. You will only reach 80 if the elements of superstructure is 5, the deck condition can be 4 and still the sufficiency rating in the 90's
Anwar Ahmad:HBP funds can be used for the followings:
FHWA issued a memorandum in 2007 to address the concern with the sufficiency rating threshold in addressing bridge decks in poor condition. In accordance with the program direction and FHWA interest in reducing the number of structurally deficient bridges, Highway Bridge Program (HBP) funds can be expended to rehabilitate or replace bridge decks with condition ratings of 4 or less regardless of the sufficiency rating of the bridge (see URL link to the memo below)
- Replacing eligible bridges (deficient status (structurally deficient or functionally obsolete) and sufficiency rating less than 50)
- Rehabilitating eligible bridges (deficient status and sufficiency rating equal to or less than 80.
- Rehabilitating or replacing bridge decks that are in poor condition regardless of sufficiency rating (see attached FHWA memo http://www.fhwa.dot.gov/bridge/071101.cfm)
- Systematic preventive maintenance (approved systematic process for cost–effective activities). Refer to FHWA Bridge Preservation Guide for additional information
- Preventive maintenance, painting, application of calcium magnesium acetate, sodium acetate/formate, or other environmentally acceptable, minimally corrosive anti–icing and de–icing compositions.
- What is the difference between epoxy and methacrylate seal overlay?
Here are some reports that provide information on bridge deck overlays including a comparative evaluation of concrete sealers and multiple layer polymer concrete overlays by Mr. Michael Sprinkle of the Virginia Transportation Research Council.
- VTRC Report "Comparative evaluation of concrete sealers and multiple layer polymer concrete overlays" http://www.virginiadot.org/vtrc/main/online_reports/pdf/88–r2.pdf
- VTRC Report "Evaluation of the Construction and Performance of Multiple Layer Polymer Concrete Overlays". http://www.virginiadot.org/vtrc/main/online_reports/pdf/87–r28.pdf
- "Guidelines for Selection of Bridge Deck Overlays, Sealers and Treatments" (completed under NCHRP Project 20–07,Task 234), may be found through AASHTO publications.
- Long–Term Performance of Polymer Concrete for Bridge Decks http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_syn_423.pdf
In Virginia we primarily use methyl methacrylate to seal individual deck cracks and map cracks along the lines of the cracks. We use epoxy overlays to seal and waterproof entire concrete decks. Note that if you have large active cracks in a concrete deck that were created by drying shrinkage you should not use an epoxy overlay, as the active cracks may cause reflective cracks in the epoxy.
- What kind of PM and scheduling VDOT used for their preservation Bridges Program?
The best way to answer your question is to provide the following chart that lays out our preferred schedule of preventive maintenance activities:
The best way to answer your question is to provide the following chart that lays out our preferred schedule of preventive maintenance activities: Activity Preferred Cycle (years) 1 Bridge Cleaning 1 2 Seats & Beam End Washing 2 3 Cutting & Removing Vegetation 2 4 Routine Maintenance of Timber Structures 2 5 Scheduled Replacement of Compression Seal Joints 10 6 Scheduled Replacement of Pourable Joints 6 7 Cleaning & Lubricating Bearing Devices 4 8 Scheduled Installation of Thin Epoxy Overlay 15 9 Beam Ends Painting 10 10 Removing Debris from Culverts 5
- What is Mix design for Joint slab?
In Virginia we have been using our normal deck concrete (designated as "A4"). The requirements for A4 concrete can be found in Section 217 of our specifications at the following link: http://www.virginiadot.org/business/resources/const/2007SpecBook.pdf
However, we are investigating the idea of adding fibers to create a concrete mix with a little more flexibility. We will probably be doing some trial joint closures with the new mix in the coming year.
- Thin polymer overlays lose their skid values rapidly here in Oregon– –even though the protective layer is intact. Adam, can you comment on how you address this issue?
The skid resistance of epoxy overlays does decrease over time, but in Virginia the deterioration rate is much slower. Typically, epoxy overlays have a bald tire number of 60 when new and 40 to 45 later in life. This still compares favorably with bare decks with no tines or saw cut grooves, which typically have numbers less than 35. It might be worth noting that we insist on two coat systems, which might have something to do with the overall good performance (more aggregate will protrude). Also, for projects where skid resistance is of particular importance, consideration should be given to specifying more angular and durable aggregates, which can increase skid resistance numbers (short term and long term) significantly.
- Are any of VDOT’s "restorative maintenance" activities funded under the SPM federal program?
In most cases the answer is no, but there are instances where restorative activities can be funded. One example is patching. Such patching activities can be funded when accompanied by system preservation elements such as sacrificial anodes and/or concrete overlays.
- When you mentioned not to use asphalt, did you mean asphalt only or asphalt plus membrane
My comments were directed at our problems with asphalt overlays without membranes. Asphalt overlays with membranes are acceptable, but our first preference is to use rigid concrete overlays with latex modified concrete or silica fume.
- Can construction scheduling software and project management procedures apply to small local government agencies?Do you allow traffic on between installations of epoxy overlays?
No. We are very strict about keeping traffic off the bridge prior to the application of the first coat and second coat of epoxy.
- What type of beam end coatings are you using for preventative maintenance projects and what type of surface prep are you using?
For coating of beam ends we provide two options. The first option is zone coating, which requires abrasive blasting to an SP10 surface treatment, followed by our standard 3 coat zinc-based coating system. This is the highly rigorous approach.
The second, much less expensive option is overcoating, which involves hand or power tool cleaning, followed by the application and use aluminum epoxy mastic paint to overcoat (this is defined as "System F" of Section 231 of our specifications – see link above).
- Is there environmental concern with washing bridges? (Adam and Anwar)
Anwar Ahmad:Adam Matteo:
Timely bridge washing activities are very cost effective in reducing deterioration rates and thus extending the service life of bridges. Environmental considerations and appropriate permitting and processes should be appropriately addressed when doing any type of work including bridge washing. Some states have worked out an agreement with their environmental discipline where they are monitoring the overall effects of washing water that is entering the stream. The monitoring period varies. At the end of the monitoring period they will be able to determine if they need to make any adjustments to their washing practices, i.e. collect the wash water and dispose of away from the stream. Other agencies are blocking all of the deck drains and are either diverting the wash water away from the stream and onto the adjacent embankment, or completely capturing all of the wash water and dispose of it away from the stream.
In Virginia we have established a blanket agreement with the Department of Environmental Quality that spells out the environmental criteria that must be followed during bridge washing. These restrictions include:
- Temporary plugging of deck drains
- Redirect washwater to the vegetation at the end of the bridge (do not let washwater feed directly into stream).
Yes. Washington State DOT publishes Programmatic Permit Guidance for maintenance activities. Bridge washing is covered by HPA GH–D9448–01. The guidance requires initial dry cleaning (sweeping and vacuuming) of bridges to collect loose materials including flaking paint. After dry–cleaning, low–pressure water washing is allowed, and water may be discharged into streams. Washington DOT is concerned about disruption of streambeds and vegetation. Bridge washing is restricted to certain months in the year, and the State Department of Fish and Wildlife must be given three–days prior notice of every bridge washing project.
- If it is not required to have BMS to use federal funds for SP projects, is it required to justify to FHWA the bang for the buck prior to using? (Anwar)
Yes. The use of BMS is highly encouraged but not mandatory. A fully functioning BMS typically includes modules such as inventory and condition, cost, deterioration, feasible actions, programming, reporting, etc. The availability of such systems facilitates the SPM process. However, in absence of a fully functioning BMS, a state may propose a process that explains their SPM program. The FHWA Bridge Preservation Guide provides information on the program attributes of an effective SPM program.
- Do you have an asphalt overlay removal program within your agencies? (Adam for VDOT program, Anwar – from a national perspective, and George for CO Program.)
I am not aware of any asphalt removal programs. Due to the high permeability of asphalt, the installation of waterproofing membrane should be considered when contemplating the installation of asphalt overlay.
VDOT does not have a formal asphalt overlay removal program in place. However, we are considering “bundled” projects to remove multiple older asphalt overlays along certain corridors. It should be noted that even within a particular corridor the most appropriate rehab/replacement alternative may vary from structure to structure. Therefore, bridges along a particular corridor where existing asphalt overlays are removed may see differing deck and overlay replacement options. We require waterproofing under all new asphalt overlays and are considering requiring that the waterproofing system be comprised of a full membrane.
Colorado uses both asphalt overlays and thin bonded concrete overlays on bridges in service. Colorado has seen good performance among decks that are protected by asphalt wearing course plus waterproofing membrane (see ). Colorado DOT often uses concrete overlays instead of asphalt+membrane because concrete overlays require maintenance less frequently.
 Service Life and Cost Comparisons for Four Types of CDOT Bridge Decks (2007). CDOT–2007–2, 118p, http://www.coloradodot.info/programs/research/pdfs/2007/bridgedecklife.pdf/view
Other available resources include:
FHWA Bridge Preservation Guide – http://www.fhwa.dot.gov/bridge/preservation/guide/guide.pdf (.pdf)
FHWA Bridge Preservation Tool Box – http://www.fhwa.dot.gov/bridge/preservation/
VDOT Bridge Maintenance Manual – http://www.extranet.vdot.state.va.us/locdes/electronic%20pubs/Bridge%20Manuals/VolumeV-Part2/Chapter32.pdf (.pdf)
Colorado Bridge Manual – http://www.coloradodot.info/library/bridge