Terminal Healthy

May 19, 2008

On Nov. 19, 2007, Runway 3R-21L at Detroit’s Metropolitan Airport (DTW) was reopened for service after receiving a major face-lift. This 10,000-ft runway is one of four parallel runways at the airport and is at the eastern boundary of the facility. Reconstruction of the runway faced challenges at every step. From the design to scheduling and construction, the owner, designer and contractors were required to pay close attention to every detail.

On Nov. 19, 2007, Runway 3R-21L at Detroit’s Metropolitan Airport (DTW) was reopened for service after receiving a major face-lift. This 10,000-ft runway is one of four parallel runways at the airport and is at the eastern boundary of the facility. Reconstruction of the runway faced challenges at every step. From the design to scheduling and construction, the owner, designer and contractors were required to pay close attention to every detail.

The team that built this project consisted of owner Wayne County Airport Authority (WCAA), designer Kimley-Horn and Associates (KHA) and general contractor John Carlo Inc. (JCI). The designer also had help from the American Concrete Pavement Association (ACPA), Connico Inc., Roy D. McQueen and Tucker, Young, Jackson and Tull Inc., to name a few. JCI managed the project and self-performed the concrete paving.

Some of the major subcontractors that helped out were Angelo Iafrate Construction, Rauhorn Electric, Soil and Materials Engineers and Cadillac Asphalt.

Windblown difficulty

One of the first challenges presented was that the two crosswind runways at the airport (which are located at the north and south ends of the airfield) and one active hanger access point intersected 3R-21L. The WCAA and associated airlines required that one of the crosswind runways and access to the hangers be maintained at all times. With these intersections, the KHA elected to make significant elevation improvements at the crosswind intersections with respect to smoothness.

The existing cross section carried the crown point of the runways through 3R-21L, making for a rough ride. The design team also had to figure out how to stage the project in a manner that would meet the owner’s demanding schedule and maintain access to a crosswind runway and the associated hangers. With that, it was decided to construct the runway in three phases.

Phase One took place in the latter half of 2006, starting on July 31, with a completion date set prior to the Thanksgiving Day rush. This included approximately 88,250 sq yd of concrete removal and replacement. To complement the concrete, the designers included an extensive edge-drain system, an asphalt base for the concrete, complete replacement of the existing electrical system (which included lighting and sign­age) and a complete reconstruction of the asphalt shoulders. This phase encompassed the northern 2,400 ft of the runway, which included the intersection of one of the crosswind runways. In an effort to save time on the future phases of the project, this phase also included the widening of a taxiway that led to the hangers that needed to be maintained. A 9-ft asphalt extension was placed on both sides of the taxiway to accommodate larger planes in the final phase of the project.

Phase Two of this project started on May 14, 2007, with the finish date scheduled for enough time to allow for the completion of Phase Three. Again, this was done to accommodate the airport for the Thanksgiving commute. This phase, the largest of the three, split the remainder of the runway in half with an active taxiway in the middle that maintained access to the hangers. The intersection of the second crosswind runway was at the south end of this phase, leaving the north crosswind (completed in ’06) open to air traffic. This phase consisted of pouring 175,000 sq yd of 17-in.-thick concrete, and also included the same scope of work as Phase One.

With the contractor focusing on the north half of Phase Two, an early opening of the second crosswind runway and early rerouting of the hanger traffic was successfully allowed and completed. This allowed the contractor an early start on Phase Three, which was the active taxiway at the midpoint of the runway. This final phase included the same scope of the previous two and included 30,220 sq yd of runway and taxiway replacement.

Never leave your site

One of the next challenges faced on this project was the concept of green construction. The designers required that all the concrete that was removed from the existing runway remain on-site. The contractor was given a site to store and crush all of the concrete material into a size that was suitable to use as a base material for the new asphalt shoulders that are adjacent to the runway and all taxiways.

JCI’s subcontractors ended up recycling approximately 290,000 tons of the existing runway. The contract also required that the existing asphalt base be removed from the project. The contractor also recycled 100% (190,000 tons) of this product back into the project. The millings from the asphalt base were used to improve the existing maintenance roadways that were used as haul routes by the contractors. This asphalt product also was used as a base material for the concrete batch plant and concrete crushing sites, and a small portion of the recycled asphalt product was used in the new asphalt mixes that were placed on the project. The contractor also elected to submit an option to the owner to utilize blast furnace slag as the coarse and intermediate aggregate in the P-501 concrete mix. The owner allowed this option, taking a financial credit and allowing an additional 110,000 tons of recycled product to be utilized on the project.

The final challenge to note in this project was the long-term durability of the P-501 concrete pavement. Currently, the ACPA, together with the Federal Aviation Administration (FAA), is developing a new P-501 concrete paving specification to meet today’s challenges. Although at the time of this project this document was not available for full use, the design team on elected to feature many of the concepts that are in this new document.

One of the concepts used was the feature of mitigating the deterioration of concrete pavements in the presence of potassium acetate deicers. It has been found that this chemical has a detrimental effect on some concrete pavements where it attacks the aggregates in the surface of the pavement, causing rapid deterioration. The specification required that the contractor do extensive testing on the concrete mix materials to ensure that this deterioration will not occur. It has been documented that the fine aggregates that are locally available are potentially reactive in the presence of the deicer. The specification stated that if in the presence of reactive aggregates, the contractor had the option to use a Class F fly ash as a cement substitute or a chemical additive called lithium nitrate (LN) to counteract the deterioration. After performing the required reactivity testing, the contractor elected to use the LN additive. Over 200,000 gal of the LN product was included in the mix throughout the project.

The new specification also shifts much of the quality-related responsibility onto the contractor. On the Detroit project, the specification required that the contractor perform mix design trial batches out of the plant, where before it had only been required in the laboratory. It has been noted that differences may be realized between the two environments. They also required the contractor to pave a small test strip prior to mainline production. The intent of this demonstration was for the contractor to show their process to the engineer and to improve the lines of communication once large-scale production began. Both tests were successful and a very useful addition to the specification on the project.

Advanced placement

This project also employed a concrete mix that was a new addition to the FAA specification and was based on a method that has been utilized in other arenas for several years. It is what the industry is calling a dense-graded mix, or “Shilstone” mix, named after Jim Shilstone, who developed the concept. The mix requires constant monitoring of the aggregates to ensure that they are always optimally proportioned. The mix allowed the contractor to decrease the total cement content of the mix to 500 lb per cu yd while still exceeding the strength requirements of the specification. The mix also gives the contractors improved workability because it is much easier for them to place and it typically requires less finishing.

Some of the other functions that the contractor had to perform were the normal air, slump and temperature tests. On this contract, the slump testing took on a slightly different form. Instead of specifying a maximum number, the documents allowed the contractor to choose their own target. This method allows the contractor to control their own destiny and if they feel that by increasing the slump they can improve placement characteristics, they have that flexibility. With all the testing, the contractor was required to maintain control charts to ensure that action limits were adhered to.

A few final new quality-control functions that were included in the concrete paving portion of this project were weather management, vibration monitoring and maturity testing. The contractor was required to install a weather station on the project to help limit the adverse effects humidity and wind can have on freshly placed concrete. JCI was required to monitor evaporation rates on a regular basis and adjust cure and paving start times to limit its impact. Along with the weather analysis, JCI utilized a computer program called Hyperpav, which analyzes specific mix designs and weather data and helps the contractor prevent early-age cracking that may occur if joints are not cut in time.

With the vibration monitoring, the contractor was required to ensure that all the vibrators on the concrete paving equipment were operating properly. In doing that, the engineer was reassured that the concrete was being properly consolidated.

Maturity testing was the final element discussed above, and was not a part of the original specification. With the challenging schedule on the project, JCI requested the allowance of this testing to improve the early-age predictions. Maturity testing was used to monitor three different strength requirements. The specification allowed the contractor to drill into the new slabs at one strength, put a paver on the slabs at another and finally open the new pavement to all traffic at a third strength level. This addition to the contract greatly improved the schedule throughout the project.

These new additions to a project of this magnitude definitely added to the complexity and work required. However, the added communication it takes to make all this work improves the team atmosphere and makes each party more accountable for its actions. Detailed plans and meetings were required to spell out how each function of the project was going to be completed. With that on the table, there were very few surprises once the actual work was performed. This all served to highlight the work that is being done to bring old standards up to the latest and greatest field practices. The contractor and engineer are required to work as a team, and that idea truly creates a better working environment for all parties involved. Finally, the end all tell all of this is that the concepts produce a quality product for the end user.

About The Author: Fowler is quality concrete control manager for John Carlo Inc., Clinton Township, Mich.

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