Complete closures versus two-lane closures were evaluated at a workshop. 

Last year, Lochner Engineering, in concert with the Washington State Department of Transportation staff, identified a major concern with timely and cost-effective replacement of aging concrete pavements. A team of paving experts from across the country convened and spent one day looking at how production could be increased, along with overall traffic impacts and costs decreased.

Two options

The discussions resulted in two primary options. The first, and best scenario for least time and cost, is a full roadway closure with construction segmented and coordinated by task. A number of variables must be considered, including weighing the impact of closure between congestion and cost, availability of materials and mix plants, early and continuing coordination with permitting and resource agencies, and a strong public information program.

The full-closure option could result in replacing up to 5 lane miles per day, including removing old concrete pavement and repairing and/or replacing base material as needed, with significantly reduced costs. It would, however, also include the potentially significant impact of traffic diversion.

The second option, providing only two lane closures at one time, increases the time for completion by nearly a factor of eight. Accompanying that much-longer period will be heavy traffic control, and the difficulties of working under flowing traffic conditions.

Agencies must also consider the individual requirements of each job site. For example, if alternative routes were very long, that would weigh heavily in favor of the second option.

Clearly, faster-than-normal replacement is feasible, and the first option is most desirable from a construction perspective. Agencies must weigh the other factors to determine which of these options it may choose.

Behind the options

We all know the issues:

- Concrete pavement on our freeways has served the public well, but will soon need replacement or other less severe refurbishment.
- Congestion is already severe on many of these roadways and construction activity will bring that congestion to extreme levels.
- There may well be a political reaction that responds to a public concern.
- The length of the disruption is proportional to the level of discontent. So, how can this duration of activity be minimized?

Lochner volunteered, in cooperation with WSDOT, to host a workshop to specifically identify the challenges and more important, to identify solutions that could be applied to overcome those challenges.

Workshop approach

We elected to convene a core group of paving experts from across Washington State and the United States. We chose to keep the core group small to allow strong participation, and back that group with a wider group of subject-matter experts for review of the initial results. We were very pleased to obtain voluntary participation from among the best experts across the country today, from Washington D.C. to Washington State.

Along with that group, we identified a Review Group of subject-matter experts from within the industry, public and private, to review the work of the Core Group and comment from their particular perspectives.

The focus was narrowed to the most difficult area, urban-area pavements. These critical areas typically carry extremely large volumes of traffic, often exceeding 200,000 vehicles per day. Not only are they very costly to work with, they also result in major traffic disruptions and significant headaches for both agency staff and elected officials.

The group identified areas that can be most readily controlled and looked for ways to streamline them. There are limiting factors, including traffic and potential detours, utilities and drainage, signing and ITS systems availability. Each of these areas will require further study. Contractor capabilities must be considered and requirements prioritized.

Both groups were advised of only general expectations. Our goal was to encourage a free flow and exchange of ideas, unconstrained by what we already know or assume about limits on the progression of work. The discussion was specifically not to be constrained by historical rules, standards, and specifications. Participants were asked to explore the solution with as few rules as possible.

Questions given to begin the thought process were:

- What is the maximum concrete pavement that can be laid in a day?
- Must the base also be routinely replaced?
- What are the limitations to production?
- How can production be increased? At what cost?
- What is the minimum cure time?
- Can cars be allowed sooner than trucks?
- Will the new concrete pavement last another 40 years?
- Should the specifications be changed?

Results

Attendees were reminded of the scope of the problem. The roundtable discussion focused only on removing pavement where necessary and replacing it with new pavement.

Participants were reminded that for the public agencies, a better understanding of the capabilities of paving contractors would allow setting more realistic goals for the time allowed for utility work, drainage, ITS, signing, and related requirements.

Scenarios were used to promote discussion. A hypothetical section of urban freeway was assumed as an urban area near Seattle. The given section was to be four lanes plus wide shoulders in each direction, 10-miles long.

Then the group was asked, “What is the minimum length of time needed to rehabilitate this section of concrete freeway during which traffic is diverted or significantly constrained?”

The group used two basic construction scenarios to begin the process. In the first case, assuming good base still exists; the existing pavement is left in place. In the second scenario, the pavement is removed to replace, repair, and/or upgrade the structural condition.

Pavement-in-Place

This option received minimal discussion, since few highway sections will have adequate vertical clearance to use overlays, and will still have sound base materials to provide adequate future structural capability, particularly considering that truck volumes and loads have increased, and are expected to increase further.  

For the left-in-place case, the group assumed unbonded concrete overlays. Advantages of this approach include:

Unbonded overlays require little or no preparation.
Existing pavement is used as a sub-base, eliminating the time and cost of subgrade removal.
The interlayer serves to isolate existing deterioration.
For locations where vertical clearance, lane alignment, and related problems do not directly allow this approach, this option will need additional study. 

The group estimated production using an interlayer of approximately 1 inch, at 2.5-lane miles per mix plant per day. Availability of mix plants becomes a key issue in any scenario. With less distance to move materials, higher production rates become more achievable.

Assuming, for example, that two mix plants could be set up at or near interchanges at each end of the project, paving production could be sustained at 5 lane miles per day. The entire project, approximated at 100 lane miles — 4 lanes + 1 shoulder x 2 directions x 10 miles — could be completed in 20 working days.

Adjustments in median barrier height, utility upgrades, and so on, would add to this duration.

Pavement-removed

Removing the pavement is a more complex process, with more operational elements. Before placing new pavement, the existing pavement must be removed, with the attendant need for waste material haul and disposal. Additionally, the subgrade will need to be lowered to allow for the deeper concrete thickness (13 inches) and the hot-mix asphalt base. Additional subgrade repairs may also be needed.

Two production timelines were built for this scenario, using different assumptions. Both were built for a 10-mile section of a four-lane roadway, having one 4-foot shoulder and one 10-foot shoulder. The first timeline assumes full roadway closure; the second, only two lanes at a time. These two options result in vastly different schedules.

Production requirements

To achieve maximum production, with disruptions, and hopefully lowest direct cost, a key set of requirements was discussed. These include:

- On-site portable concrete plants are required to minimize travel time and avoid traffic conflicts. To accomplish this will require political and environmental concurrence far in advance.
- Even with the on-site plants, existing plants will likely be used. A dedicated route for trucks to avoid conflicts will be needed with local agency concurrence.
- Environmental controls for items such as dust, noise, and materials handling/storage must be evaluated and a plan approved in advance.
- An adequate supply of cement and surfacing materials must be assured.
- Large staging areas for storage of the removed concrete are essential. They must have close proximity to the work and dedicated travel routes.
- Crushing and recycling of the old concrete is very desirable. Work in Texas has shown this to be successful. Crushed material may not be available in time for the first 10-lane miles but could be used for the next 10. High-compressive strengths (up to 16,000 psi) of existing pavements make it very attractive to reuse. Performance issues with using recycled concrete in new concrete needs to be fully investigated.
- Weather is critical and the schedule is dependent on no rain. This is in part why the two-lane option was discussed also as a possible two-season project.

Traffic options

With multiple tasks, sequencing became the focus of the discussion. The sequence is best viewed as a flow diagram. Two different options were covered.  One was full closure of the highway. A second option requiring only closure of two traffic lanes at any given time was also covered. Consideration of these two options provides an excellent foundation for decision makers.

Full traffic closure assumes full closure of the entire roadway. Where this approach has been used, rates of production have risen dramatically and construction savings have been significant. Any consideration of this approach should include the cost of congestion and the level of inconvenience for the traveling public along with the cost savings. It is quite possible that while it may cause considerable congestion and delay during the project, it is the best overall solution.

The group developed a timeline diagram, which shows the five basic tasks and the required duration to complete the hypothetical 10-mile, four-lane each-way freeway segment.

A basic assumption was made that every day would be a working day with two 10-hour shifts per day. Crew size on any shift would depend on logistics required for operations. Time estimates for each task were based on a total of eight crews working each day. Four crews would work an early shift and four a late shift, with each crew working on one task during a given shift. Depending on the sequence and tasks, more than one crew could be working on the same task at different locations.

The production rate for concrete pavement removal was estimated at 1-lane mile per crew per shift, or 8-lane miles per day. On Day One, Shift One, removal of the existing pavement starts. Expected time to complete all removal of the pavement on the entire 10 freeway miles is 10 shifts.

On Day One, by the end of Shift One, existing concrete pavement removal would progress far enough that subgrade removal and any needed structural repairs could start on Shift Two.

Base removal of a 13-inch depth was estimated to be 6-lane miles per day Expected time for this work, is 12 shifts.

By Day Three, the removal process is far enough ahead that other crews can begin to place the new base material.

On Day Five, placing the hot-mix asphalt base would start. Replacing the base with 6 inches of material was estimated at 2-lane miles per day per crew, or 8-lane miles per day.

Finally, starting Day Six, placement of the new Portland cement concrete pavement could begin and be completed in 24 shifts, or 12 working days.

Using full closure, complete removal of the existing pavement, base replacement, and structural repairs, followed by new PCC paving, could be completed in less than 20 days, or about the same time as simply performing a structural overlay. Overall production rate could be 5-lane miles per day.

These production rates do not necessarily include complications that may arise at interchanges or with material supplies.

Two-lane closure assumes partial closure, which would require significant traffic control that the first timeline avoids. With only partial roadway closure, the process also goes from simultaneous to consecutive.  Only one lane is worked on each cycle, and existing pavement removal, base repairs, and replacement must be completed before the new pavement is placed. Under these assumptions, participants conceived a different timeline. It shows the first phase, which would only include one direction, or four lanes.

Removal of the existing pavement begins on Day One, with five days for completion.

On Day Six, subgrade excavation can begin with eight days for completion.

Base materials replacement can begin on Day 14, with five days for completion.

Hot-mix asphalt placement in these first four lanes can begin on Day 14, with four days to complete.

The subtotal for concrete removal and base preparation for one lane of the freeway would be 22 days. After this process is complete on one side, it must be repeated for lane two for a subtotal of 44 days.

PCC surfacing may be done two lanes at one time, requiring 22 days ending with a 66-day total for the first two lanes. Shoulders were not included in this estimate, and an additional 10% is added to provide for that work.