Rapid Slab Repair and Replacement of Airfield Concrete Pavement (2021)

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92 Examples of Rapid Slab Repair and Replacement Projects This appendix provides examples of RSRR projects and lessons learned from visiting con- struction sites and discussions with contractor personnel, construction inspectors, and airport personnel. Each case example provides the following with respect to RSRR practice at each featured airport: • Project overview, • Construction observations, and • Discussion. Table B-1 lists the examples of RSRR projects. The examples are arranged from west to east and according to FAA region and associated LTPP climate region (FHWA 2016). Full-Depth Repair at San Francisco International Airport Project Overview The project at San Francisco International Airport (SFO) project consisted of replacing nine 25- by 25-foot concrete slabs (5,625 square feet) that were exhibiting midpanel and corner cracking. The slabs serve as an engine startup pad for wide-body aircraft and are located on a taxilane that serves Concourses A and B. The startup pad was originally constructed in August 2017, and cracking was observed in some of the slabs a few weeks after construction. Airfield operations had discussed replacing these slabs, but the work was postponed until 2020 because of construction on the adjacent Concourse B. Since 2017, the airport has monitored the panels and performed small slab repairs as needed. In 2020, the airport was able to conduct the FDRs as a change order to an existing FDR project on an adjacent concourse. This allowed the project to be quickly executed, and the on-site contractor and design team were able to produce plan sheets and details. It also allowed the use of a concrete mixture from the adjacent construction project, with minor modifications. The construction process included removal of the damaged concrete and base reconstruction. Stakeholder coordination began 2 months before construction and involved weekly meetings with approximately 30 people. Effective stakeholder communication and coordination allowed the engine startup pad to be closed to aircraft operations for a continuous 30-day period, which was accomplished by using temporary taxilanes and vehicle service roads to steer traffic around the closure. This allowed the contractor to replace multiple slabs in the same construction sequence with an HES, fiber-modified P-501 concrete mixture, which was deemed a more practical mixture than the VHES mixtures typically used for overnight closures. Figure B-1 shows the project location on the airfield. A P P E N D I X B

Examples of Rapid Slab Repair and Replacement Projects 93   Figure  B-2 shows the concrete finishing operation and a finished slab ready for curing compound. Table B-2 provides general information about this project. Construction Observations Demolition The slab perimeter was saw cut at least 1 day prior to slab removal. The construction time frame permitted the use of the breakup and removal method. The contractor used two exca- vators with jackhammer attachments to break the slabs into pieces, which were removed by another excavator. The on-site engineer reported no damage to adjacent slabs. The existing base and subbase layers were also removed in preparation for the new pavement section. During demolition, the exposed subgrade surface was saturated with rainwater, which required the removal of an additional 6  inches of subgrade material prior to the rebuilding of the pavement structure. Preparation The exposed subgrade material was recompacted to 95% compaction (a nuclear gauge was used to verify density). According to project drawings, a Class II, nonwoven, medium-weight fabric was placed on the existing subgrade followed by a geogrid. A 12-inch-thick P-219 recycled concrete aggregate base course was installed, followed by a 5-inch P-306 lean concrete base layer (see Figure B-3). The surface layer was a 21-inch HES P-501 portland cement concrete Airport FAA Region LTPP Climate Region RSRR Type San Francisco International Northwest Mountain Wet, nonfreeze FDR Seattle–Tacoma International Northwest Mountain Wet, nonfreeze FDR Phoenix Sky Harbor International Western Pacific Dry, nonfreeze PDR/FDR Gerald R. Ford International Great Lakes Wet, freeze PDR Cincinnati/Northern Kentucky International Southern Wet, freeze PDR/FDR Table B-1. Examples of RSRR projects. Source: Google, n.d. Work Area Figure B-1. Project location at San Francisco International Airport.

94 Rapid Slab Repair and Replacement of Airfield Concrete Pavement Source: Nichols Consulting Engineers, Chtd. Figure B-2. Example of cast-in-place full-depth repair at SFO: (a) finishing after placement and (b) finished texture. Category Detail Airport location San Francisco, California Owner City and County of San Francisco FAA classification Large hub FAA region Western Pacific LTPP climate region Wet, nonfreeze Facility and location of work Taxilane between Concourses A and B Closure Time 30 days Type of work FDR Dates of construction January 7–30, 2020 Site visit weather conditions Temperature: 50°F to 55°F Humidity: 80% Wind: <5 mph Sunny, rained before paving and contractor had to drain site Work performed by Contractor Construction drawings and specifications? Yes Emergency work? No, but the airport wanted to get the work done expeditiously Table B-2. General information: Project at San Francisco International Airport.

Examples of Rapid Slab Repair and Replacement Projects 95   with synthetic macrofibers and microfibers and steel reinforcement. FDRs were not performed during a single overnight or daytime closure and, consequently, the contractor needed a contin- gency plan to remove rainwater from the construction site. This was done by using pumps with installed sedimentation control measures; an example from an adjacent work area is shown in Figure B-3. Load-Transfer Restoration Dowel bars were placed at transverse joints and at slab edges abutting existing concrete. The 1.5-inch-diameter epoxy-coated dowels were 20 inches long and spaced 18 inches on center. Dowel bar baskets were used for transverse contraction joints. For construction joints, a gang drill was used to simultaneously drill two or three dowel bar holes at a diameter of 1⁄8  inch greater than the diameter of the dowels. Dowels at the corners of slabs were hand drilled, which resulted in misaligned dowel bars in some instances. Plans called for drilled dowels to be a minimum of 3 inches from the old dowel bars, which were cut off and remained in the existing concrete. The drilled holes were cleaned by means of compressed air, and the dowels were anchored into the holes with two-part paste epoxy (but without retention disks). Figure B-4 shows installed dowel bars. Concrete Mixture The contractor used a 6,000 psi (compressive) HES P-501 concrete with an added blend of synthetic macrofibers and microfibers (combined dosage of 5 pounds per cubic yard) for shrinkage and secondary reinforcement. The design properties and mix proportions of the concrete mixture are summarized in Table B-3 and Table B-4, respectively. Concrete Placement The concrete was mixed and delivered to the site in ready-mix trucks. The concrete mix was very flowable, with slump measurements ranging from 6.5 to 7.0 inches. To ensure proper placement, concrete was pumped into place at a rate of 1 to 2 cubic yards per minute. Consolidation was done with a stinger vibrator and by hand using shovels. Ready-mix trucks fed the concrete pump Source: Nichols Consulting Engineers, Chtd. Figure B-3. Preparation at SFO: (a) placement of lean concrete base course and (b) rainwater removal.

96 Rapid Slab Repair and Replacement of Airfield Concrete Pavement Source: Nichols Consulting Engineers, Chtd. Figure B-4. Installed dowel bars at SFO: (a) dowel bar assembly for contraction joints, (b) dowel bars as a construction joint, (c) dowel bars offset from cut dowel bars, and (d) misaligned dowel bar. Property Typical Value Compressive strength (psi) at 28 days 6,000 Specified slump (in.) 6 to 7 Design air (%) 2.0 w/cm ratio 0.33 Table B-3. Design properties of SFO concrete mixture.

Examples of Rapid Slab Repair and Replacement Projects 97   truck, which placed concrete to half the slab depth. Concrete was consolidated, and then the reinforcing steel mesh was placed. The remainder of the concrete was placed and consolidated, and a power screed was used to level the slab surface and establish the final grade. Figure B-5 illustrates the concrete placement procedure. Finishing and Curing. A roller tamper was used to depress coarse aggregate and to achieve a more uniform surface finish. The finishing process continued with the use of bull floats and a broom finish. A water-and-wax-based, white-pigmented curing compound was applied after finishing. Figure B-6 shows the steps for finishing, texturing, and curing. Joints. A lightweight saw was used to create 0.25-inch-wide by 4-inch-deep contraction joints as soon as the slabs were deemed solid enough to minimize spalling. Joints were later cut to a final depth of 7 inches, equivalent to 1⁄3 of the slab depth (Figure B-7). Material Testing The HES concrete was required to have a flexural strength of at least 650 psi at the time it was returned to service. This was not a concern given the 7-day cure time and total 30-day closure time allotted to complete the FDRs. Discussion Observation of the construction of the FDRs provided the following insights. These obser- vations were supplemented by on-site discussions with contractor and airport personnel, along with follow-up correspondence. • Advanced coordination with all stakeholders was paramount to successful delivery of the airfield slab replacement. Stakeholder coordination began 2 months before construction and involved weekly meetings with approximately 30 people. Some of the critical components that made this project a success were good communication and coordination with stake- holders to schedule and carry out the taxilane closure. The longer closure time allowed the contractor to maximize efficiency in slab placement and not be burdened with having to cut, Proportion per yd3 Materials ASTM Weight (lb) Volume (ft3) Fine Aggregate 1 C33 895 5.47 Fine Aggregate 2 C33 407 2.35 Coarse Aggregate #57 C33 1,375 7.65 Coarse Aggregate #7 C33 500 2.78 Type II/V cement C150 799 4.06 Class F fly ash — — — Potable water C1602 267 4.28 Air content 0.54 Total 27.13 Note: Admixtures (optional—to be added upon request): • ASTM C494 Type B and D 2 to 6 • ASTM C494 Type C 10 to 45 Table B-4. Proportions of concrete mixture used in SFO project.

98 Rapid Slab Repair and Replacement of Airfield Concrete Pavement remove, and replace one or two slabs per night, which would have been the case if the work had been completed in multiple nighttime closures. The continuous placement of multiple rows of slabs also improved construction quality and will likely contribute to a longer-lasting product. • Use of an existing design team and on-site contractor accelerated the overall slab replace- ment process. A design team and contractor were already on-site replacing concrete slabs at the adjacent boarding areas. The airport executed a change order to the existing contract that significantly shortened project delivery. The design team was able to prepare a single plan sheet modification to the boarding area construction plans, and the contractor was able to Source: Nichols Consulting Engineers, Chtd. Figure B-5. Concrete placement sequence in SFO project: (a) placing concrete, (b) placing and consolidating concrete at dowel bar assemblies, (c) installing reinforcing steel, and (d) screeding concrete.

Examples of Rapid Slab Repair and Replacement Projects 99   quickly schedule and execute construction. The crews were familiar with the existing site conditions, had the necessary security badges, were familiar with the slab replacement pro- cess, and had experience working with the HES concrete mixtures. • Safety and security required a significant commitment of airport personnel. Barricades surrounded the working areas—both portland cement concrete and asphalt replacement— and on the closed portion of the taxilane. Airport operations vehicles continuously secured all work areas. The contractor and airport coordinated in advance so that plenty of airport operations personnel were on-site to provide escort for construction activities. Source: Nichols Consulting Engineers, Chtd. Figure B-6. Concrete surface finishing, texturing, and curing in SFO project: (a) roller tamping, (b) surface finishing and edging, (c) broom finishing, and (d) surface with curing compound (macrofibers are present in the finished surface).

100 Rapid Slab Repair and Replacement of Airfield Concrete Pavement • Proper use of personal protection equipment (PPE) was essential for both contractor and airport employees. This was most evident when the contractor was air-blasting holes for dowel cleaning and for mixing two-part epoxy for dowel anchoring. • The concrete mixture was reviewed by the airport’s pavement consultant, who advised the contractor to add synthetic microfibers and macrofibers. The concrete mix was delivered on time and met the specifications for consistency and compressive strength. Since the air temperature was in the low 50s (°F), a nonchloride accelerator admixture was used in the concrete mixture. • Providing the contractor with a secured area in which to work enabled the paving to be completed well ahead of schedule. The contractor was able to mobilize the sawing and slab removal operations on a large scale. This also allowed sufficient staging of concrete trucks, which successfully delivered up to 120 cubic yards of concrete to place three slabs per day. Full-Depth Repair at Seattle–Tacoma International Airport Project Overview This nonemergency project was carried out to replace three concrete apron slabs at commercial gate D11, where the existing slabs were demolished and replaced with VHES concrete. Originally, a single 9-hour daytime closure (8:00 a.m. to 5:00 p.m.) was allotted for FDR. However, during slab removal, an unexpected pipe was uncovered, which required an additional 9-hour closure the following day for removal. Figure B-8 provides an overview of the project location, and Table B-5 provides general information for this project. Source: Nichols Consulting Engineers, Chtd. Figure B-7. Contraction joint saw cuts in SFO project.

Examples of Rapid Slab Repair and Replacement Projects 101   Construction Observations Demolition SEA inspectors had previously identified three slabs for replacement under an accelerated construction schedule. The slabs were cut into approximately 20 pieces with a concrete saw the day before scheduled construction. Two expanding lift anchors were pounded into holes drilled into each piece, followed by lift-out with an excavator. Figure B-9 provides images of the slab removal process. The slab was saw cut into smaller pieces, and holes were drilled for lifting pins. Next, wood wedges were driven into the saw cut joint around the slab to be removed to help prevent damage to adjacent concrete during the lift-out process. Finally, the pieces were lifted. During demolition, a portion of the slab being removed was found to be heavily reinforced. The contractor tried several methods to remove these pieces but ultimately used a hydraulic Work Area Source: Google, n.d. Figure B-8. Project location at Seattle–Tacoma International Airport. Category Detail Airport location Seattle, Washington Owner Port of Seattle FAA classification Large hub FAA region Northwest Mountain LTPP climate region Wet, nonfreeze Facility and location of work Apron area at commercial gate D11 Closure time Daytime (8:00 a.m. to 5:00 p.m.) Type of work FDR Dates of construction September 25–26, 2019 Site visit weather conditions Temperature: 60°F to 68°F Humidity: 60% to 75% Wind: 5–8 mph Cloudy sky Work performed by Contractor Construction drawings and specifications? No Emergency work? No Table B-5. General information: Project at Seattle–Tacoma International Airport.

102 Rapid Slab Repair and Replacement of Airfield Concrete Pavement breaker. The reinforced concrete was found to be a cap for an existing vertical steel tube. SEA inspectors were unable to determine the purpose of the abandoned pipe. The hydraulic breaker worked well, but demolition of this highly reinforced concrete turned out to be a time-consuming effort that took several hours. As a result, concrete placement was delayed until the next day, and the contractor backfilled the repair area with aggregate base and placed a steel plate over the aggregate. The removal process is shown in Figure B-10. Preparation After the pipe and surrounding concrete were removed, the base material was tested for chemical contaminants with a handheld electronic odor detector device. Contaminated base material would have been removed and replaced with new base material; however, contaminants Source: Nichols Consulting Engineers, Chtd. Figure B-9. Sequence of removal of existing cracked slab at SEA: (a) slab saw cut into pieces and holes drilled for lifting pins, (b) wooden wedges driven into joints to prevent damage to adjacent slabs, and (c) slabs lifted with an excavator and loaded onto a trailer.

Examples of Rapid Slab Repair and Replacement Projects 103   were not detected. The existing base was leveled with the excavator bucket and compacted with a vibratory plate. Density testing with a nuclear gauge was performed, with a target of 100% compaction. Dowel bars were installed along all four sides of each repair area. Holes were drilled into the existing slabs with a truck-mounted four-barrel drill. Several tubes of epoxy were squeezed into a bucket and mixed by using a drill with mixer attachment. Dowel bars were dipped into the mixed epoxy and slid into the drilled holes. Grout retention discs were installed over each dowel bar (against the slab) to prevent the epoxy from seeping out. A steel reinforcement mat was installed at slab middepth in all the repair areas. Sequential preparation of a repair area for concrete placement is shown in Figure B-11. Source: Nichols Consulting Engineers, Chtd. Figure B-10. Removal of reinforced concrete portion and top of abandoned pipe at SEA: (a) existing condition, (b) demolition of concrete, (c) cutting of metal pipe, and (d) pipe removal completed.

104 Rapid Slab Repair and Replacement of Airfield Concrete Pavement Concrete Mixture The contractor used a VHES concrete containing a proprietary CSA-based cement binder and locally available aggregates. The mix was proportioned to achieve the minimum required opening-to-traffic flexural strength of 650 psi at opening. Concrete was mixed on-site using mobile (volumetric) mixers with electronic controls. The exact concrete mixture design proper- ties and proportions were not available, but typical values for VHES mixture design properties and mixture proportions are summarized in Table B-6 and Table B-7, respectively. Concrete Placement Two mobile mixers simultaneously discharged concrete along one side of the repair area. Mobile mixer trucks slowly pulled forward and placed concrete to a height just above the adjacent slabs. Once both mobile mixers had discharged their concrete loads, a third mobile Source: Nichols Consulting Engineers, Chtd. Figure B-11. Preparation of repair area prior to concrete placement at SEA: (a) checking density, (b) drilling dowel bar holes, (c) dowel bar installation (note proper use of epoxy retention discs), and (d) reinforcement installed and ready for concrete.

Examples of Rapid Slab Repair and Replacement Projects 105   mixer was used to fill the rest of the repair area, which required about ½ to 2⁄3 of its load. The first few cubic feet of concrete out of the mobile mixer were typically dry (lacked proper water proportion), which prompted the operators to make a judgment-based adjustment to the mix water. After slight adjustments, the concrete material became more fluid and consistent. A roller screed was used to level and partially consolidate the concrete while a concrete vibra- tor was used to consolidate the concrete near the slab edges. The contractor ensured that the concrete was properly consolidated. Finishing and Curing A hand-tooled edge was formed adjacent to the existing portland cement concrete slabs. Afterward, a hand float was used to smooth and densify the concrete surface, and a broom finish was applied to provide surface texture. Approximately 10 to 15 minutes after finishing was completed and the surface had begun to set, water was manually sprayed on the concrete surface. This was followed by placement of a garden sprinkler to continuously apply water to the slab surface for an additional 30 minutes. An overview of the VHES concrete placement, finishing, and curing is shown in Figure B-12. Material Testing Several concrete beams were cast from the middle of the load from the second mobile mixer truck for each repair area. Beams were left to field-cure until approximately 30 minutes prior to Property Typical Value Flexural strength (psi) at return-to-service for 100% payment 650 Slump (in.) 4.25 Air (%) 5.9 Unit weight (lb/ft3) 142.8 w/cm ratio 0.45 Maximum aggregate size (in.) 1.5 Table B-6. Typical design properties of VHES concrete mixtures at SEA. Proportion per yd3 Materials ASTM Weight (lb) Volume (ft3) CSA cement C1600 705 3.83 Coarse Aggregate No. 467 C33 1,799 10.80 Washed coarse sand C33 1,092 6.62 Water 275 4.41 Air 1.35 Total 27.00 Note: Admixtures: • Air entrainer at 2 ounces/hundredweight (oz/cwt) • Water reducer at 4 oz/cwt • Citric acid in solution at 1.4 oz/cwt • Stabilizer at 0.3 oz/cwt • Lithium nitrate solution at 9 oz/cwt Table B-7. Typical proportions of VHES concrete mixtures at SEA.

106 Rapid Slab Repair and Replacement of Airfield Concrete Pavement the first strength test. Two beams were tested on the first repair slab at 3.5 hours with an average flexural strength of 850 psi, which greatly exceeded the flexural strength requirement of 650 psi at time of opening. The average 3.5-hour flexural strength for the second slab was 685 psi. The contractor was allowed some freedom in how quickly the VHES mixture reached opening strength. A contractor that can perform the demolition work quickly may opt for a slower-curing VHES concrete mixture; alternatively, a contractor that struggles with the demolition work may desire a faster-curing VHES concrete mixture to allow for more time for demolition. Discussion Observing the construction of three FDRs to replace cracked slabs in a commercial gate area provided several insights. Observations were supplemented by on-site discussions with the con- tractor and SEA personnel. Source: Nichols Consulting Engineers, Chtd. Figure B-12. Overview of VHES concrete placement at SEA: (a) initial concrete placement, (b) screeding of concrete, (c) finishing of concrete, and (d) initial (moisture) curing. The finishing process began immediately following the screeding.

Examples of Rapid Slab Repair and Replacement Projects 107   • Advanced coordination with all stakeholders was paramount to successful delivery of rapid airfield slab repairs. With this project occurring directly outside a gate, coordination with the airline was critical in securing a daytime closure that would not significantly impact the airline’s operations. SEA inspectors were in constant communication with airline repre- sentatives once it was apparent the concrete would not be placed and cured before the end of the closure. The airline was able to secure a second daytime closure on the following day for FDR completion. • Safety and security required a significant commitment of airport personnel. SEA operations vehicles continuously monitored and secured the work site. The work site was in a corner of the airport that received low traffic and SEA personnel made sure no nonconstruction vehicles or personnel entered the construction area. • Proper use of PPE was essential for both contractor and airport employees. Excellent use of PPE, including vests, hard hats, gloves, eye and ear protection, boots, and respirators (when warranted), was noted on this project. • Protection of existing concrete during demolition was a challenge. Slabs were saw cut into manageably sized pieces to minimize damage to adjacent concrete. Adjacent slabs were fur- ther protected by wood wedges installed into the saw cut joint to act as buffers from swaying concrete pieces as they were removed. Some minor damage still occurred to adjacent concrete. • Overall work-site cleanliness was important to minimize FOD. The contractor laid plastic sheeting around the area to be replaced to keep the adjacent work area clean; this not only made cleanup easier but also minimized tracking of construction debris to locations outside the work area. • An initial volume of concrete produced by a mobile volumetric mixer should be discharged and disposed of off-site. The first few cubic feet of concrete produced by the mobile mixing trucks was consistently dry and required judgment-based adjustment of mix water to obtain a workable concrete. After this adjustment, the concrete was consistent for the remainder of the discharge for that truck. • Upfront planning and preparation were important for placement of ESC. Three mobile mixing trucks were required to produce enough concrete for each FDR: two mobile mixers working simultaneously produced most of the material required, while a third mobile mixer produced the remainder of the concrete necessary to fill the repair area. Continuous placement was necessary because of set times. • Being prepared for unexpected circumstances was an essential element of rapid FDR. Removal of an unexpected reinforced concrete pipe cap delayed concrete placement until the following day. The contractor was able to backfill the repair areas with aggregate base and cover them with steel plates to allow the airline to use the gate between construction closures. • Awareness of the construction schedule (during construction itself) was very important. Site-specific conditions (known or unknown) may slow the production rate and ultimately affect a contractor’s ability to complete construction within the allotted time frame. • Attention to detail during construction was essential. The contractor paid attention to many construction details, such as use of grout retention discs on dowel bars, wetting the base material prior to concrete placement, and verifying steel reinforcement depth. In-Pavement Light Can Replacement, Full-Depth Repair, and Partial-Depth Repairs at Phoenix Sky Harbor International Airport Project Overview This project replaced in-pavement light can fixtures on the centerline of Runway 7R-25L that were settling below the pavement surface (considered to be an FDR). Additional work inside the runway safety area included preventive electrical maintenance, conversion to LED runway

108 Rapid Slab Repair and Replacement of Airfield Concrete Pavement lighting, and repair and replacement of some runway electrical circuits. After many months of stakeholder communication and coordination, the runway was closed over a single weekend (from Friday 10:00 p.m. to Monday 7:00 a.m.). During the closure, the airport’s maintenance crew took the opportunity to perform other maintenance activities, including removing tire rubber, striping, and completing PDRs on the runway pavement. Figure B-13 provides an over- view of the project location, while Figure B-14 shows replacement of the light can and a PDR. Table B-8 provides general information for this project. Construction Observations for In-Pavement Light Replacement and Full-Depth Repair Demolition A 54-inch-diameter core bit was used to drill around the defective light can through the 24-inch-thick concrete pavement in advance of core removal. The core was removed by bolting Source: Google, n.d. Work Area Figure B-13. Project location at Phoenix Sky Harbor International Airport. Source: (a) Rummel Construction and (b) Nichols Consulting Engineers, Chtd. Figure B-14. In-pavement light can replacement at PHX: (a) FDR and (b) PDR.

Examples of Rapid Slab Repair and Replacement Projects 109   four steel plates with rings to the concrete. Chains were hooked to the steel plate rings and to the arm of the backhoe, and the pavement core (with light can) was lifted out. Figure B-15 shows the removal sequence of the concrete core that contained the in-pavement light can. According to the contractor, the main challenge was lifting out the core vertically to avoid causing damage to the adjacent concrete. A crane was used first but was not able to vertically remove the core. The contractor decided to use a backhoe and subsequently was able to remove the large core without damaging the existing concrete. Category Detail Airport location Phoenix, Arizona Owner City of Phoenix FAA classification Large hub FAA region Western Pacific LTPP climate region Dry, nonfreeze Facility and location of work Runway 7R-25L Closure time Weekend (Friday 10:00 p.m. to Monday 7:00 a.m.) Type of work In-pavement light replacement, FDR, and PDRs Dates of construction November 1–4, 2019 Site visit weather conditions Temperature: 54°F to 60°F Humidity: 20% to 30% Wind: 0–2 mph Clear sky Work performed by In-pavement light replacement and FDR: Contractor PDR: Airport personnel Construction drawings and specifications? In-pavement light replacement: Yes PDR: No Emergency work? No Table B-8. General information: Project at Phoenix Sky Harbor International Airport. Source: (a) Rummel Construction and (b–d) Nichols Consulting Engineers, Chtd. Figure B-15. Removal sequence of in-pavement light can at PHX: (a) coring, (b) lift-pins installed, (c) lift-out, and (d) removal complete.

110 Rapid Slab Repair and Replacement of Airfield Concrete Pavement Preparation After core removal, concrete pieces that had broken off the core were removed from the repair area. Electricians cleaned the electrical conduits that were filled with water and mud, and all excess water was removed from the repair area prior to installation of the new in-pavement light can fixture. An isolation joint was created with preformed joint compression material, and a reinforcing cage was installed around the light can. The light can was suspended from a beam flush on the pavement surface to set final elevation. Concrete Mixture The contractor used a 6,500 psi HES concrete with a nonchloride accelerator. The design properties and mix proportions of the concrete mixture are summarized in Table B-9 and Table B-10, respectively. The concrete mixture proportions were not adjusted for the volume of chemical admixtures. Concrete Placement A ready-mix truck delivered 4 cubic yards of concrete; only 2 cubic yards were placed in the FDR surrounding the new light can. The temperature of the concrete at the time of place- ment was 75°F with a slump of 6.75 inches. The concrete was consolidated with a mechanical vibrator. Property Typical Value Compressive strength (psi) 6,500 Specified slump (in.) 3–8 Design air (%) 1.5 Unit weight (lb/ft3) 147.5 w/cm ratio 0.32 Table B-9. Design properties of PHX concrete mixture. Proportion per yd3 Materials ASTM Weight (lb) Volume (ft3) Fine aggregate C33 1,093 6.69 Coarse aggregate C33 1,750 10.61 Type II/V cement C150 650 3.31 Class F fly ash C618 215 1.58 Potable water C1602 275 4.41 Air 0.41 Total 27.0 Note: Admixtures: • ASTM C494 Type F High-Range Water Reducer at 66 oz/yd3 • ASTM C494 Type A Water Reducer at 26 oz/yd3 • ASTM C494 Type C Accelerator as requested Table B-10. Typical proportions of VHES concrete mixture at PHX.

Examples of Rapid Slab Repair and Replacement Projects 111   Finishing and Curing Finishing was done by hand with a trowel. A spray-applied, wax-based curing compound was used for this work. After application of the curing compound, a wet burlap covering was placed on top to help cure the concrete surrounding the in-pavement light (Figure B-16). Material Testing The HES concrete was required to have a compressive strength of at least 6,000 psi at the time it was returned to service. This was not a concern, given the use of an HES concrete along with approximately 50 hours for curing before reopening the runway. The 24-hour, 48-hour, and 7-day average compressive strengths were 6,020, 7,440, and 8,140 psi, respectively. Construction Observations for Partial-Depth Repairs Demolition The observed PDRs for this project were performed by using the chip-out method to expose and repair retrofitted electrical conduits that had collapsed and caused a short circuit. Figure B-17 shows an example of a marked area slated for PDR (over retrofitted electrical conduit) and the demolition and preparation process. First, the repair area was demolished by jackhammer to expose solid concrete. After concrete pieces were removed, a dry saw was used to saw cut a smooth edge around the repair boundary about 1.5 to 2 inches from the damaged area. A vacuum was used to remove dust and small pieces of concrete. Preparation The airport maintenance crew thoroughly cleaned the area of dust and debris and removed any moisture. Previous experience with this repair material indicated that the presence of dust, small aggregates, or moisture could cause early failure of the PDR. Prior to placement of the Source: (a) Rummel Construction; (b) Nichols Consulting Engineers, Chtd. Figure B-16. FDR finishing and curing in-pavement light at PHX: (a) trowel finishing and (b) final curing with use of wet burlap. A wax-based curing compound was applied prior to the installation of the wet burlap covering.

112 Rapid Slab Repair and Replacement of Airfield Concrete Pavement Note: Cleaning repair area with a vacuum is not shown. Source: Nichols Consulting Engineers, Chtd. Figure B-17. PDR demolition sequence at PHX: (a) area marked for PDR, (b) chip-out demolition method, (c) sawing a clean face, and (d) prepared area (exposed electrical conduit).

Examples of Rapid Slab Repair and Replacement Projects 113   repair material, the existing transverse joint was reestablished with preformed joint compression material (Figure B-18). Materials and Installation The PDR repair material used for this project was a proprietary, two-component polymer concrete that uses fine aggregate as an extender. During cold weather, the airport adds an accel- erator by the same manufacturer. The airport also adds a small portion of aggregate, as it believes the aggregate improves durability. Mixing was done according to the product manufacturer’s instructions with a rotating bucket mixer with a paddle inserted to blend the material. The process began with a 5-gallon bucket of fine aggregate and ended after the addition of both parts of the binder material and mixing for a specified amount of time. Figure B-19 depicts the polymer concrete mixing process for the selected product. The PDR material appeared to be consistent and flowable when poured from the 5-gallon buckets into the clean repair area (Figure B-20). The material remained workable while it was hand troweled to finished grade and did not set up too quickly. Consolidation was not required for this type of self-leveling PDR material, nor was curing required for this polymer concrete material; the set time was approximately 15 minutes after mixing. Discussion Observing PDR and FDR construction for replacement of in-pavement light provided the following insights. These observations were supplemented by on-site discussions with the con- tractor and airport personnel and by follow-up correspondence. • Advanced coordination with all stakeholders was paramount to successful delivery of rapid airfield slab repairs. The stakeholder planning for this project started in April 2019, Source: Nichols Consulting Engineers, Chtd. Figure B-18. Preformed joint compression material used at PHX to reestablish transverse joints.

114 Rapid Slab Repair and Replacement of Airfield Concrete Pavement approximately 7 months prior to the start of construction. Some of the critical components that made this project a success were good communication and coordination with stakehold- ers to schedule and carry out the runway closure. This allowed project work to be carried out prior to the busy holiday season. • Safety and security required a significant commitment of airport personnel. Barricades were placed in all working areas and on the closed taxiway intersections. To improve safety and security, airport operations vehicles continuously secured all work areas. The contractor and airport coordinated in advance so that plenty of airport operations personnel were on-site to provide escort for construction activities. Source: Nichols Consulting Engineers, Chtd. Figure B-19. Mixing process for polymer concrete used at PHX for PDR: (a) electric mixer, (b) binder (Part 1) added to aggregate, (c) binder (Part 2) added, and (d) mixing.

Examples of Rapid Slab Repair and Replacement Projects 115   • Proper use of PPE was essential for both contractor and airport employees. Use of respirator equipment was especially important during drilling and cleaning of holes for dowel bars. • A major challenge during the planning phase was approval of the concrete and additives to be used for the concrete mix. The FDR concrete mix was delivered on time and met the specifications for consistency and compressive strength. Since the air temperature was in the low 50s (°F), a nonchloride accelerator admixture was used in the concrete mixture. • The local experience of airport maintenance crews played an important role in the longevity of PDRs. Airport maintenance crews understood that the presence of any moisture, dust, or debris on the concrete surface that was prepared for repair could cause premature failure of the repair. The crews paid close attention to cleaning and drying the repair area prior to placement of the repair material. • Being prepared for unexpected circumstances was an essential element of rapid slab repair. A crane was not able to vertically lift the concrete core (containing the in-pavement light can) without risking damage to the adjacent concrete. The contractor quickly adjusted its approach and used a backhoe to successfully remove the concrete core. • Awareness of the actual PDR completion rate compared with closure time was very important. Demolition for the PDRs took longer than anticipated, since the previously placed repair material was in sound condition. The crews had to be careful not to demolish more repair areas than could be completed (repair material placed and cured) prior to the end of the scheduled closure. Partial-Depth Repair at Gerald R. Ford International Airport Project Overview As part of a larger apron expansion project at Gerald R. Ford International Airport (GRR), PDRs were performed on the passenger terminal apron to repair spalls. The spalls resulted from winter snowplowing operations and improper edge finishing during concrete placement. Source: Nichols Consulting Engineers, Chtd. Figure B-20. Material installation at PHX for PDR: (a) placement, (b) spreading, and (c) leveling.

116 Rapid Slab Repair and Replacement of Airfield Concrete Pavement PDR work was carried out during multiple daytime work shifts. Partial or full apron closures were not utilized, mainly because of the reduction in aircraft traffic resulting from the COVID-19 pandemic. Stakeholder coordination allowed daytime construction in specified areas during periods with no (or minimal) aircraft operations on the terminal apron. Figure B-21 provides an overview of the project location, and Table B-11 provides general project information. Construction Observations Demolition and Preparation The contractor and project engineer walked every concrete joint within the project limits and marked locations for PDRs. If a spall was less than 1 inch from the face of joint, loose concrete material was removed for joint resealing. If the spalled area exceeded the 1-inch criterion, it was treated as a PDR. In this case, the contractor saw cut a rectangular area that extended 1 inch past the limits of the spalled (or potential spall) area. The material inside the boundaries was removed by making several overlapping saw cuts with a wide-blade concrete saw to a depth of 2 to 3 inches. The repair area was thoroughly cleaned and dried with compressed air prior to Source: Google, n.d. Work Area Figure B-21. Project locations at Gerald R. Ford International Airport. Category Detail Airport location Grand Rapids, Michigan Owner Gerald R. Ford International Airport FAA classification Small hub FAA region Great Lakes LTPP climate region Wet, freeze Facility and location of work Terminal apron Closure time Daytime (hours varied) Type of work PDR Dates of construction Various (site visit on July 21, 2020) Site visit weather conditions Temperature: 72°F Humidity: 56% Wind: 5 mph Partly cloudy Work performed by PDR: contractor Construction drawings and specifications? PDR: Yes Emergency work? No Table B-11. General information: Project at Gerald R. Ford International Airport.

Examples of Rapid Slab Repair and Replacement Projects 117   placement of the PDR material. Previous experience indicated that cleaning and preparation were important to the quality of PDR. Figure B-22 shows the demolition sequence. The contractor watched the daily flight schedule via the GRR airport mobile app and coordi- nated PDR work with airport operations staff. PDRs were completed between peak flight times, and the contractor had a spotter watching for aircraft operating on the apron. Materials and Installation The PDR repair material used for this project was a two-component, epoxy-based elastomeric concrete that uses fine aggregate as an extender. Mixing was done according to manufacturer instructions with a paddle attachment affixed to an electric drill. Two binder components were measured, added to a 5-gallon bucket, and blended. Fine aggregate was added to the blended binder and mixed again. Figure B-23 shows the elastomeric concrete mixing process for the selected product. The PDR material was manually poured from the 5-gallon buckets into the clean repair area (Figure B-24). According to the contractor, the material remained workable while it was hand- troweled to a finish grade and did not set up too quickly. Consolidation was not required for this type of self-leveling PDR material, nor was curing required for this elastomeric material. The joint was reestablished by dry sawing (hand grinder) the hardened repair material, followed by cleaning and resealing of the joint. The PDR was returned to service within 2 hours. Figure B-25 shows a completed PDR with sealed joints. Discussion Visiting a PDR construction site at GRR provided the following insights. These observations were supplemented by on-site discussions with the contractor, project engineer, and airport personnel, along with follow-up correspondence. • This airport has an aggressive approach to maintaining airfield concrete pavements. Approxi- mately $500,000 is spent annually for PDR and FDR. Source: (a) Nichols Consulting Engineers, Chtd. and (b and c) Ajax. Figure B-22. PDR demolition sequence at GRR: (a) marked location of PDR, (b) sawing, and (c) area prepared for PDR.

118 Rapid Slab Repair and Replacement of Airfield Concrete Pavement • Coordination with all stakeholders was paramount to successful delivery of rapid airfield PDRs. The contractor monitored the daily flight schedules and coordinated work locations and timing with airport operations. This allowed daytime PDRs during periods with no (or minimal) aircraft traffic. • Closures were not needed, owing to proper planning and coordination with stakeholders. The contractor worked when aircraft were not at the gates or using the apron, and repairs were opened to traffic within 2 hours of material placement. • The contractor’s attitude toward quality work and implementation of quality control was very important. The contractor believed that attention to detail during construction results in longer-lasting PDRs. The contractor performed follow-up inspections of concrete slabs in the work areas and re-marked spalls that were missed during construction and PDRs that needed to be corrected. • Monitoring weather was important because the area is in a rainy climate. The contractor monitored the weather forecast and did not start PDRs if rain was imminent. Source: Ajax. Note: The joint was reestablished and resealed following the specified material curing time. Source: Ajax. Figure B-23. Mixing process for elastomeric concrete used at GRR for PDR: (a) add binder components, (b) mix binder, and (c) add aggregate and mix. Figure B-24. Installation sequence at GRR for PDR material: (a) place material, (b) level material, and (c) self-consolidation.

Examples of Rapid Slab Repair and Replacement Projects 119   Full-Depth and Partial-Depth Repairs at Cincinnati/Northern Kentucky International Airport Project Overview As part of a multiyear repair project at Cincinnati/Northern Kentucky International Airport (CVG), deteriorated concrete slabs associated with Runway 9/27 and Taxiways K and J were identified for repairs. Cracking and spalling were the major drivers triggering the need for PDR and FDR. Typical slabs are 25 by 25 feet by 18 inches thick. The first portion of work was performed on the taxilane along the Concourse B apron (Ramp 3). The Ramp 3 taxilane work was originally planned for nighttime closures, but with reduced operations as a result of the impact of COVID-19, the airline using the apron was able to relocate gate operations, and the work was completed over an extended closure. Future phases of repair work are anticipated to be on an accelerated schedule. Although this phase was not accelerated, there are still lessons to be learned. Figure B-26 provides an overview of the project location, while Table B-12 provides general information for this project. Construction Observations for Full-Depth Repair Demolition First, the slab perimeter was cut, and then the slabs were further cut into approximately 16 pieces prior to slab removal. The contractor indicated that interior saw cuts are often performed at a slight angle to facilitate removal of the first piece. Removal was done by installing lift anchors into holes drilled into one piece that was then lifted out with an excavator. Subsequent pieces were removed with an excavator. Figure B-27 provides images of the slab removal process. Wood wedges were driven into the saw cut joint around the slab to help prevent damage to adjacent concrete during the removal process. Source: Nichols Consulting Engineers, Chtd. Figure B-25. Example of completed PDR with sealed joint at GRR.

120 Rapid Slab Repair and Replacement of Airfield Concrete Pavement Preparation During slab removal, some of the stabilized base was bonded to the underside of the slab and left a portion of the base damaged. Any areas of base damage were replaced with concrete after slab removal (the existing base was lean concrete or asphalt). Dowel bars were installed along the entire perimeter of the repair areas. Holes were drilled into the existing slabs with a 4-gang pneumatic dowel drill. Epoxy was injected into the drilled holes and dowel bars were inserted. Retention discs were installed over each dowel bar (and against the slab) to prevent the epoxy from seeping out. Dowel bar baskets were anchored at interior transverse joint locations for consecutive slab replacements. A double application of curing compound was applied to the stabilized base as a bond breaker. Sequential preparation of a repair area for concrete placement is shown in Figure B-28. Concrete Mixture The contractor used a conventional concrete and locally available aggregates. The mix was proportioned to achieve the minimum required opening-to-traffic flexural strength of 650 psi at Source: Google, n.d. Work Area Figure B-26. Taxilane project location at Cincinnati/ Northern Kentucky International Airport. Category Detail Airport location Hebron, Kentucky Owner Kenton County Airport Board FAA classification Medium hub FAA region Southern LTPP climate region Wet, freeze Facility and location of work Apron taxilane at commercial gates Closure time Daytime Type of work PDR and FDR Dates of construction September 22 through December 10, 2020 (Ramp 3); observed on October 26, 2020 Site visit weather conditions Temperature: 47°F to 51°F Humidity: 77% to 93% Wind: 0–12 mph Cloudy sky Work performed by Contractor Construction drawings and specifications? Yes Emergency work? No Table B-12. General information: Project at Cincinnati/ Northern Kentucky International Airport.

Examples of Rapid Slab Repair and Replacement Projects 121   28 days. Concrete was mixed adjacent to the airfield with the use of a batch plant and delivered to the work site by nonagitated dump trucks. Typical values for mixture design properties and mixture proportions are summarized in Table B-13 and Table B-14, respectively. Air content and slump tests were conducted from random loads in determined sublots. Flexural strength beams were also produced for later testing. Concrete Placement As mentioned previously, the concrete mixture was mixed at an adjacent batch plant and delivered to the work site in nonagitated dump trucks. To facilitate placement, a material transfer vehicle was used to place the concrete. Consolidation was performed with internal (or spud) vibrators. A roller screed was used to level the concrete surface and establish final grade. Figure B-29 illustrates the procedure for FDR concrete placement. Note: Shims installed at slab edges to prevent damage to adjacent slabs. Source: C&S Engineers, Inc. Figure B-27. Removal sequence of existing cracked slab at CVG: (a) sawing slabs into smaller pieces, (b) lift-pin holes drilled into slab pieces, (c) lift-pins installed, and (d) slab pieces removed.

122 Rapid Slab Repair and Replacement of Airfield Concrete Pavement Source: (a) C&S Engineers, Inc., and (b) Applied Pavement Technology, Inc. Figure B-28. Preparation of repair area at CVG prior to concrete placement: (a) drilling of holes for dowel bars and (b) curing compound applied as bond breaker and dowel bars installed. Property Typical Value Flexural strength (psi) at 28 days for 100% payment 650 Slump (in.) 4 max.a Air (%) 5.5 w/cm ratio 0.38–0.45 Maximum aggregate size (in.) 1.5 aFor hand placement. Table B-13. Typical design properties of CVG concrete mixture. Proportion per yd3 Materials ASTM Weight (lb) Volume (ft3) Type I/II cement C150 282 1.43 Slag cement C989 282 1.59 Coarse Aggregate No. 57 C33 1,552 9.29 Coarse Aggregate No. 8 C33 221 1.34 Natural sand C33 1,380 8.34 Water 220 3.53 Air content 1.49 Total 27.0 Note: Admixtures: • ASTM C260 Air-Entraining Admixture at 1.3 oz/cwt • ASTM C494 Water Reducer at 3 oz/cwt Table B-14. Typical proportions of CVG concrete mixture.

Examples of Rapid Slab Repair and Replacement Projects 123   Finishing and Curing A bull float and edging tools followed the roller screed. Surface texture was applied by a broom finish. A white-pigmented curing compound was applied after finishing was completed. Joints Interior transverse joints were saw cut to a depth of 1⁄3 the slab thickness. Joints were then widened to 0.5 inch at the surface to create the joint sealant reservoir and beveled. Construction Observations for Partial-Depth Repair Demolition and Preparation Figure B-30 shows an example of a marked area slated for PDR and the demolition and preparation process. The perimeter of the repair area was saw cut (minimum depth of Source: Applied Pavement Technology, Inc. Figure B-29. Overview of FDR concrete placement at CVG: (a) loading concrete into a belt placer, (b) placing concrete, (c) consolidating concrete, and (d) screeding concrete.

124 Rapid Slab Repair and Replacement of Airfield Concrete Pavement 2.5 inches) approximately 2 inches beyond the edge of damaged concrete. The deteriorated material was removed with a jackhammer to expose sound concrete, and the repair area was thoroughly cleaned to remove dust and small pieces of concrete after removal of the larger pieces. Materials and Installation The PDR repair material used for this project was a three-component (A + B + C), epoxy-based elastomeric concrete consisting of elastomeric activator and patch (A + B) and aggregate (C). Mixing was done manually and in accordance with product manufacturer instructions. The two binder components were added to the 5-gallon bucket of aggregate and blended. A two-component (A + B) bonding agent was applied to the surface of the repair area immediately prior to placement of PDR material. The PDR material was manually poured from the 5-gallon buckets into the clean repair area (Figure B-31). The surface of the repair was then trowel finished. Consolidation was not required for this type of self-leveling PDR material, nor was curing required for this elastomeric material. The joint reservoir and sealant were reestablished after the material hardened. Discussion The following observations were made, supplemented by on-site discussions with the contractor and project engineer: • Coordination with all stakeholders was paramount to successful delivery of rapid air- field PDRs. Although this project was initially planned as nighttime work, coordination with stakeholders (regarding COVID-19 reduction in aircraft operations) allowed the first phase of work to be performed during an extended daytime closure. An extended closure allowed for a less time-sensitive environment in which to demonstrate techniques and materials that will be used in future phases. • Safety and security required a significant commitment of airport and contractor personnel. Barricades were placed in all working areas to prevent airfield traffic from entering work Source: C&S Engineers, Inc. Figure B-30. Demolition and preparation at CVG for PDR: (a) location marked for demolition and PDR and (b) area ready for repair material.

Examples of Rapid Slab Repair and Replacement Projects 125   Figure B-31. Installation of PDR material at CVG: (a) area prepared for repair material, (b) placement of repair material, and (c) finished PDR. zones and construction traffic from entering active airfield facilities. As part of the project requirements for safety and security, the contractor hired airport staff (off-duty police, fire, and maintenance personnel familiar with the airfield) to continuously monitor all work areas. The contractor also staffed a dedicated security gate and provided escort for construction activities. • Local experience with repair materials played an important role in the longevity of PDRs. The airport and contractor both had experience with the PDR material and understood the requirements for preparation, placement, and curing. • Repair plans needed to be well-defined. As work progressed, the quantity of PDR increased significantly from initial plan quantities, which required assessing the available budget and repair types. Source: C&S Engineers, Inc.

Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America’s Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration GHSA Governors Highway Safety Association HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S. DOT United States Department of Transportation

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