| Soil types |
- Recognize that soil types in the area will dictate design elements.
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- There is deep sand below the river and bedrock to approximately 100 feet.
- Glacial till and clay occur on both sides of the river, with alluvial silts closer to river.
- Shale at 20-40 feet was found nearby at the Rock River.
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| Proposed design |
- Address the number of proposed bridge structures.
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- Look at the structures on the Illinois side.
- Recognize that four structures on the Iowa side, not including 53rd Street, will likely be kept.
- Decide on the Mississippi River Bridge.
- Prepare for nine new bridge locations.
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| Goals of group |
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- Identify new methods and materials.
- Incorporate performance specifications.
- Minimize pavement noise and settlement times.
- Reduce snow maintenance.
- Provide for long life pavements (50 years).
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| Quarries |
- Determine what the nearby quarries hold.
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- There are limestone and dolomite quarries nearby.
- 3-I aggregates are suitable for 30- to 40-year pavement design lives.
- With good aggregates, expect a 40-year design with the local freeze/thaw cycle.
- Consider construction-related issues with over-vibrating in the past.
- Look at fine aggregates (Mississippi sand).
- No problems with ASR.
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| Pavement types |
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- PCC pavement is likely.
- Consider long life pavements.
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| Aggregates |
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- Have experienced problems with porous aggregates and cherts.
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| Existing pavements |
- How will/do they hold up?
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- Most older and problem pavements have been replaced. Most were thin by modern standards.
- Over vibration has been a typical problem due to an overly-sticky mix. Over-vibration causes a reduction in air voids and leads to rapid deterioration.
- New specs tend to hold up better than older specs.
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| Span of bridge |
- Need a 710-foot clear span.
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- Is less than existing span of approximately 750 feet.
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- Modeled span in Kentucky using a barge simulator. The determination is that the existing span is essentially the minimum needed today. This has influenced bridge type selection. The truss bridge was eliminated by aesthetic and maintenance issues.
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| Settlement/Settlement control |
- Consider existing settlement problems.
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- Can't discuss settlement too much without boring logs. It's the same with walls and the existing foundations.
- There do not appear to be settlement problems on the existing roadway.
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| Settlement/Settlement control |
- Determine if there are large fills.
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- If there are no large fills, there will not be as much settlement.
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| Settlement/Settlement control |
- Utilize accelerated settlement techniques such as lightweight fill and wick drains.
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- Pre-load fill areas as soon as possible to allow for settlement. This is less expensive.
- Consider lightweight fills such as geofoam, foam concrete and expanded slag.
- Note that the lightweight fills do not respond well in flood conditions.
- Remove and replace compressible soils. Consider in-situ improvements of the compressible soils: utilize geopiers or stone columns. Stone columns facilitate drainage, but they are expensive.
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| Settlement/Settlement control |
- Address settlement over culverts and trenches.
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- Need to control settlement, particularly at these locations.
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| Water table |
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- Not expected to be high around here.
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| Geopier versus reinforced soil foundation |
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- Consider using a reinforced soil foundation: it out-performs the geopier, settles more uniformly, is quicker and less expensive, and provides for uniform settlement.
- Remember that reinforced soil foundation is an engineered fill.
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| Design life of pavements |
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- PCC design life is 40 years, including an overlay at 20 years.
- Longer deck lives are currently being looked into on other projects. May want to investigate these methods.
- High-performance concrete was used on the I-235 structures.
- The owners should consider optimizing the gradation of the mix regardless of PCC or ACC.
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| Existing I-74 pavement |
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- An overlay was done in 1991 or 1992.
- Owners should consider an analysis of the pavement on the bridge deck to determine how well the pavement has held up.
- Generally, the States try to recycle the asphalt and use it as a trainable base.
- States probably won't be able to use recycled asphalt on the mainline due to the use of slag and polymers. They may be able to use it on side roads and shoulders.
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| Local mix |
- Determine the optimal mix.
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- There is a local source of steel slag that is used relatively often.
- The modified binder is 70/28.
- Consider a 12-inch improved subgrade layer and as much as 2 feet of base. Could crush existing concrete to C6, add fabric if open and cap with three-inch fillings of RAP material.
- Drainage is most important in pavement life and design.
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| Composite mix |
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- Have had bad experiences with CRCP.
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| Construction speed |
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- Recycle pavement in place.
- Address staging issues: staging is key to recycling in place. However, there may be limited usage for RAP on this project.
- Is doable: local contractors have the ability to recycle in place.
- Rubblize existing pavement with asphalt on top to speed construction.
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| Aggregate |
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- Iowa typically uses crushed dolomite.
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| Staging |
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- This project mirrors a project near D.C. (Woodrow Wilson Bridge). May want to consult with Maryland and Virginia about staging issues.
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| Layers |
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- Need a pavement support layer (subbase) and a subgrade layer. Combine these layers into one layer of about 12 inches.
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| Geotextiles |
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- Iowa DOT has not used geotextiles in the past. However, IDOT may be open to using these in the future. IDOT has used geogrid in panel walls.
- Geotextiles are a big advantage: they facilitate drainage and separation and are very inexpensive.
- Must keep the fines from flowing into the geotextile.
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| Recycling of pavements in place |
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- Do not want to see fines in the drainable layer on this project (or at all underneath pavements).
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| Pavement noise |
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- Consider longitudinal tining.
- Use noise quieting technologies: HMA is quieter.
- Consider an open graded asphalt mix to reduce noise, though there is a lot of maintenance with this mix.
- Make the pavement sections thicker. It is more expensive but adds longer life. Consider CRCP with a wearing course.
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| Subdrains |
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- Do not use fabric with subdrains.
- Extend subdrain outlets around the mowing line: they are being crushed by the mowers.
- Need a longer drop to speed the water velocity from the subdrain to the outlet. Now it is only six inches in 20 to 25 feet. Deep ditches may help to speed water velocity (cleaning drains) from the subdrain to the outlet.
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| Snow removal |
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- Could see an increase in crashes on the bridge approaches due to higher traffic speeds without ice on the bridges.
- Expedite ASR.
- Avoid the use of anti-icing-susceptible dolomites.
- Heat the bridge decks or snow storage areas.
- Allow snow storage on the shoulders and bikeway, as they are not being used during snow conditions.
- Implement automated temperature sensing devices in bridge decks to 1) warn drivers of icy conditions, and 2) initiate anti-icing measures.
- Use geothermal heat.
- Consider double bridge decks for snow removal.
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| Cements |
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- Type 1 and 2 are readily available and likely to be used.
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| Pavement marking maintenance |
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- Avoid the use of tapes, unless grinding is used.
- Use pavement markers that cannot be peeled off by plows.
- Remember that tape does not give the visibility of reflectors.
- Use better quality castings for RPMs.
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| Maintenance |
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- Use paraffin to repel graffiti. Coarse textures on walls are not preferred for graffiti.
- Design/build/maintain. Let the contractor clean the drains.
- Check out Highways for Life: they may provide the opportunity for increased maintenance funding.
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| Materials |
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- Verify the steel grade to be used: 50, 70 or 100 grade. Vibration problems using 100 grade have been observed. It might be better to use 50 or 70 grade steels.
- Consider high-performance weathering steel (A710, Grade B). It is available in both 50 and 70 grade.
- If the bridge is painted, choose a bridge color that is not susceptible to fading.
- Use new ideas in limited applications to observe performance. Research previous use and applications. Utilize the technology that has been tested but not used (practice is 20 years behind technology).
- Look at steel fiber in concrete. May increase tire wear.
- Use modular decking to accelerate construction. Limit cast-in-place.
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| Materials |
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- Consider weldable reinforcement bars, either epoxy coated or bare, like Illinois uses. See spec A706.
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| Foundations and retaining walls |
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- Consider using a shallow foundation: it's 1/3 the cost to install and should be considered in locations of no water and good soil. Note: Illinois has made an effort to remove spread footings.
- Use geosynthetic reinforced soils for retaining walls.
- Load test during the design phase.
- Evaluate dredging hydraulic fill as an option for the embankments.
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| Cost and life cycle considerations |
- Determine the expected life of the project.
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- Remember that the public may accept higher initial costs for a higher-quality product. However, the functional life of the project must also be considered.
- Determine whether four lanes in each direction on the bridge are necessary.
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| Existing bridge footings |
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- The bridge is situated on spread footings. Bedrock is not extremely deep at this location.
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| Contract group suggestions |
- Address job/project size.
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- Limit the size of the projects to $30 million. The smaller the job size, the more contractors that can bid, lowering the cost and potentially allowing more local firms to get the work. May have trouble breaking the project down into many $30 million projects. Also, local firms are often not big enough to take on large projects anyway.
- Consider tied projects (optional).
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| Contract group suggestions |
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- Use warranties and factor in long-term costs.
- Conduct field trials of construction materials before implementation.
- Provide for QA/QC implementation and oversight.
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| Structures group suggestions |
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- Expect brine on the bridge. Select building materials and design accordingly.
- Determine bridge type preference.
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| Structures group suggestions |
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- Depends largely on bridge type.
- Determine if there's a preference for the use of box beams on the crossroad structures. There've been some bad experiences with older box beam structures. Grout keys accumulate moisture, need better cover, etc.
- Evaluate whether cost may be a benefit of using box beam structures.
- Consider dual design for smaller structures and approaches.
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| Structures group suggestions |
- Incorporate corrosion protection.
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- Select a high-corrosion protection package.
- Use a spray-on poly-urea coating for concrete and steel. Use low permeability concrete, weathering steel or coated rebar.
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| Structures group suggestions |
- Select walls/foundations.
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- Look at shallow foundations to reduce costs.
- Use a modular block face or full height panel with GRS walls.
- Load test during the design phase.
- Investigate options for heating the deck (geothermal).
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- Coordinate with traffic group.
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- Link temperature detectors with ITS applications (message boards).
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| Public involvement group suggestions |
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- Provide for aesthetics on walls.
- Consider fadability when selecting the bridge treatment.
- Recognize that controlling aesthetic treatments or providing maintenance may be difficult.
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| Construction group suggestions |
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- Note that delivery of pre-assembled materials by barge is dependent largely on bridge type.
- Determine whether the construction group has issues with the GRS walls and field trials.
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| Construction group suggestions |
- Minimize vibration and noise.
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- May have to limit working hours in residential land use areas.
- Use shallow footings to reduce vibration.
- Consider using highway helpers to maintain traffic flow.
- Have an active law enforcement presence in the construction zone.
- Consider how to control traffic in the work zone. Find innovative techniques to properly and adequately sign the work zone.
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| Maintenance |
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- Consider grass types that have limited growth to reduce maintenance needs.
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| Questions and comments from other groups |
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- Use project sequencing and accelerated construction techniques.
- Due to price, focus accelerated construction on critical areas such as the downtown side roads.
- Implement field trials: use local roads early in the project to test materials (as opposed to mainline areas).
- Think about traffic control device requirements while under construction. Plan traffic control accordingly with respect to staging.
- Limit contract size: small contracts may create problems with managing individual projects. The more contracts on a project, the more 'drop dead' dates should be considered.
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| Questions and comments from other groups |
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- Consider the ease of removing pavement markings.
- Plan for Highway Helpers and law enforcement on site.
- Explore a system which will convey driver speed.
- Consider variable speed limits within the construction zones.
- Utilize the temperature sensors and warning devices that are planned for the project.
- Minimize 'ghost markings,' pavement markings with respect to older drivers, etc.
- Consider pavement marking durability. Could you imbed plastic markings into the pavement? Note that plastics don't stick to PCC pavements very well.
- Consider using epoxy markings: they work well in dry weather but not in wet conditions. Consider alternative pavement marking systems.
- Consider ITS to reduce response times and improve incident management.
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| Questions and comments from other groups |
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| Questions and comments from other groups |
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- Do not want to see brine used on the bridge decking but conceded that it will likely be used.
- Stated that design for the smaller structures and approaches is not economical from an engineering viewpoint.
- Want to investigate a heated bridge deck.
- Planning on a high-corrosion protection package.
- Noted that Iowa does not typically care for shallow foundations.
- Agree that pile load testing should be utilized.
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