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6 Over the past few years, several transportation agencies have focused their efforts on accel- erating construction and reducing user delay/vehicle operation times, and thereby improving overall project cost-effectiveness and reducing disruptions. To achieve this goal, agencies have used specific construction practices, manufacturing processes and technologies, design tech- niques, materials and construction equipment, project financing, contracting practices, and performance measures. While some practices are well researched and documented, up-to-date information regarding the construction and rehabilitation of concrete pavements under traffic conditions is limited to a few high-profile projects and publications. Because the construction and rehabilitation of concrete pavements under traffic is largely associated with proper management of the construction work zone, a review of work zone management and issues to consider is presented first in this chapter. This is followed by a review of six specific aspects of construction and rehabilitation of concrete pavements under traffic: â¢ Maintenance of traffic; â¢ Project planning and construction staging; â¢ Materials and design; â¢ Equipment and operations; â¢ Project management, delivery, procurement, and payment; and â¢ Communications and outreach. Work Zone Management A significant aspect of construction and rehabilitation of concrete pavements under traffic is work zone management and associated considerations. In 2004, the FHWA published updates to the work zone regulations at 23 CFR 630 Subpart J. Referred to as the Work Zone Safety and Mobility rule, it applies to all state and local governments that receive federal-aid highway fund- ing. The impetus for developing this rule was the growing congestion on many roads and the need to perform rehabilitation and reconstruction work on roads under traffic. To help agencies understand and implement the provisions of the rule, the FHWA developed four guidance documents, including Work Zone Impacts Assessment: An Approach to Assess and Manage Work Zone Safety and Mobility Impacts of Road Projects (FHWA 2006). The guidance document presents an overview of different work zone impact considerations (see Table 1), all of which are directly applicable to construction and rehabilitation of concrete pavements under traffic. C H A P T E R 2 Considerations and Strategies for Constructing and Rehabilitating Concrete Pavements Under Traffic
Considerations and Strategies for Constructing and Rehabilitating Concrete Pavements Under Traffic 7 Table 1. Overview of different work zone impact considerations (FHWA 2006). Areas of Consideration Items to Consider Project characteristics Project type Project size, extent, duration, complexity Roadway classification Area type (urban, suburban, rural) Travel and traffic characteristics Traffic demands and volume Seasonal and temporal variation in demand (hourly, daily, weekly) Occurrence of special events Percentage of different vehicular volumes (autos/single-occupancy vehicles, high-occupancy vehicles, trucks, or buses) Type of travel (commuter or tourist), freight corridor, transit corridor Public and private facility access issues Potential impacts of weather Other similar characteristics Corridor, network, and community issues Impacts of the project at both the corridor and network levels, including parallel corridors, alternate routes, the transportation network, other modes of transportation, and impacts of other work zones in the vicinity of the project, either at the corridor level or the network level Impacts on nearby transportation infrastructure, such as key intersections and interchanges, railroad crossings, public transit junctions, and other junctions in the transportation network Impacts on evacuation routes in the vicinity of critical transportation or other infrastructure Impacts on affected public properties, including parks, recreational facilities, fire stations, police stations, and hospitals Impacts on affected private properties, including businesses and residences Design, procurement, and construction options Temporal alternatives for work performance such as season, month, day of the week (weekend versus weekday), and time of day (nighttime versus day, off-peak versus peak) Alternative lane closure strategies such as full closure, partial closure, crossovers, multiple lane closure, single-lane closure, and impact of alternative traffic management strategies on lane closure decisions Alternative design solutions that address the durability and economy of maintenance of the roadway Alternative design solutions and strategies that affect decision making on right-of-way acquisition Alternative construction staging plans and construction techniques and methodologies (e.g., accelerated construction techniques) that may have varying types and severities of work zone impacts Alternative contracting methodologies such as designâbuild, A+B bidding, and incentive/disincentive provisions Work zone design and safety issues Cross-sectional issues such as lane widths, shoulder availability and widths, and number of lanes available for travel Longitudinal issues such as taper widths, taper lengths, and stopping sight distance Horizontal and vertical sight distance Project signing and advance warning Roadside devices and safety Work area separation, channelization, and protection (e.g., positive separation, barrels, cones, clear zone considerations, construction zone intrusion detection) Work area and worker delineation (visibility, retroreflectivity, etc.) Work site access and access points Visibility issues (e.g., nighttime work, lighting, fog) Curvature and gradientâvertical and horizontal Speed (posted speed limits, speed zoning, etc.) Work zone enforcement (e.g., use of uniformed police officers or patrol cars, active enforcement using radar guns or automated enforcement) (continued on next page)
8 Construction and Rehabilitation of Concrete Pavements Under Traffic Many software tools are available to assess the impacts of roadway construction work zones on traffic. Figure 1 shows some of these tools, ranging from simple to complex. Generally, the more complex tools have higher costs and require longer development time and training, but they provide greater functionality and level of detail. Maintenance of Traffic A key aspect of construction and rehabilitation of concrete pavements under traffic is manag- ing the work zone, particularly as it pertains to MOT. In Guide to Concrete Overlays: Sustain- able Solutions for Resurfacing and Rehabilitating Existing Pavements (3rd Edition), Harrington and Fick provide meticulous guidelines for managing concrete overlay construction work zones Areas of Consideration Items to Consider Temporary traffic control strategies Traffic safety and capacity requirements Alternate route scenarios Potential impacts on other corridors, nearby intersections/interchanges, and the larger transportation network Project signing and advance warning Lane closure types and strategies (full closure, lane-width restrictions, crossovers, positive separation, etc.) Work zone and work area configurations Traffic safety and control checklists for developing an MOT plan Transportation operations strategies Deployment of intelligent transportation system technologies for work zone traffic monitoring and management Provision of real-time traveler information to the public, including web- based information Application of transportation systems management and corridor management strategies, including mitigation treatments for alternate routes (e.g., traffic signal timing adjustment on affected corridors) and alternate modes (e.g., public transit subsidies, incentives, and special programs) Coordination of transportation management with existing regional transportation management centers Conducting of mobility and safety reviews and audits Speed enforcement and management in work zones using either police officers or automated techniques Traffic incident management plans for work zones Policies on work zone traffic management during emergencies (e.g., hurricane evacuations) Public information strategies Provision of project and work zone information prior to the commencement of the work in order to make the public aware of the expected work zone impacts and the agencyâs actions to mitigate the impacts Recommendations to the public on commuter alternatives, such as information on alternate routes or modes Provision of information on changing conditions on the project during implementation (e.g., changes in lane closure scenarios, construction staging, construction times, or alternate routing) Obtaining public input for the development of appropriate work zone impact management strategies during the planning and design phases of the project and for refinement of the strategies during project implementation and obtaining feedback on work zone and project performance following project completion Dissemination of information through brochures, pamphlets, and media sources, including newspapers, television, radio channels, and websites Public meetings and hearings Coordination and cooperation with affected public and private parties Table 1. (Continued).
Considerations and Strategies for Constructing and Rehabilitating Concrete Pavements Under Traffic 9 under traffic and procedures for accelerating construction of concrete overlays. They assert that âmanaging work zones for concrete overlay projects is no more challenging than for any other paving project under traffic, as long as certain straightforward practices are followedâ (Harrington and Fick 2014). Effective work zone management requires a comprehensive plan that ensures the safety of workers and roadway users and reduces disruption to the traveling public, while maintaining the cost-effectiveness of the project and long-term performance of the roadway/pavement. Table 2 shows key MOT considerations for concrete pavement construction and rehabilitation work zones. A work zone MOT guide developed by the Maryland State Highway Administration (MDSHA) adapts the Ohio DOTâs Policy on Traffic Management in Work Zones: Interstate and Other Freeways (Ohio DOT 2000) to provide advantages and disadvantages of each of a number of MOT strategies (see Table 3). The MDSHA work zone MOT guide also recommends that when construction staging/ phasing may result in unacceptable traffic impacts, other strategies should be considered. These include (1) corridor/network management using temporary traffic signals, signal timing opti- mization, and reversible lanes; (2) demand management using transit service improvements and carpool incentives; and (3) work zone intelligent transportation systems (ITSs) using dynamic late lane merge and dynamic speed limit signs. Strategies for Maintenance of Traffic One well-documented concrete construction project with traffic in the adjacent lane was a two-lane concrete overlay project on U.S. Highway 18 in Chickasaw and Fayette Counties in Iowa (see Figure 2). The 19-mi project also included edge-drain installation, full-depth repairs, bridge rehabilitation, and guardrail upgrades. Part of this research project, which was sponsored by FHWA, the National Concrete Pavement Technology Center at Iowa State University (CP Tech Center), and Iowa DOT, set out to demonstrate and document the design and construction of concrete overlays on two-lane roadways while maintaining two-way traffic. The CP Tech Center monitored the design and construction procedures and documented lessons learned during the concrete overlay construction (Cable 2012). Seventy-one design and construction recommenda- tions were developed and presented in the report. Another informative reference is that of Simon et al., who conducted a detailed evaluation on expediting highway construction while retaining quality (Simon et al. 2002). These strategies address MOT, project planning and staging, design, contracting and procurement, construction, and many other issues. Figure 1. Tools for modeling work zone impacts on traffic (Hardy and Wunderlich 2008).
10 Construction and Rehabilitation of Concrete Pavements Under Traffic Areas of Consideration Items to Consider Traffic management Capacity analyses (e.g., lanes required, length of queues anticipated) Time restrictions (e.g., peak hours, seasonal peaks) Limits to work areas Capacity of detour routes Work vehicle access and worker parking Bicycle and pedestrian traffic Warning sign locations (e.g., detours, long queues, intersecting roads) Railroad crossings and train schedule Nighttime delineation and illumination Signals, turning lanes, bus stops Traffic service (e.g., residential or business) Future rehabilitation Safety Work zone crash rates Traffic management strategies Interstate system Congestion Nighttime work Large trucks Workers on foot Pedestrians Local experience Emergency planning Incident management plans Emergency medical assistance Accidents, breakdowns, tow trucks Severe storms and storm water runoff Emergency closures Utility interruptions State police Local law enforcement Table 2. Concrete work zone MOT considerations (Harrington and Fick 2014). A number of strategies for MOT relevant to constructing and rehabilitating concrete pave- ments under traffic are discussed in the following [Cable (2012), Simon et al. (2002), and Harrington and Fick (2014)]: â¢ Multiple approaches to MOT, including partial- and full-detour options, should be generated and their impacts on construction and traffic evaluated. MOT plans drive the project schedule and affect the impact of construction on traffic operations, but too often the first workable MOT is used. â¢ MOT plans should be developed through partnering between design and field organizations to ensure that agency traffic impact goals in terms of safety, delays, closures, and so forth are met, while allowing for sufficient room for construction operations. Partnering between the agency and contractors for the purpose of developing MOT plans can lead to a more schedule- efficient approach and to more efficient design and construction. â¢ Agencies should specify that contractors prepare the MOT plan based on minimum require- ments. Constraints on the contractors should be reduced by allowing or requiring them to develop an acceptable MOT plan prior to start of field construction. â¢ Worker and work zone safety should be a top priority. MOT plans, traffic control devices, signs, and markings that clearly guide roadway users through construction zones should be used. Personnel involved in selecting, placing, and maintaining work zones should be properly trained. Design, construction, and MOT plans should aim to minimize work zone
Considerations and Strategies for Constructing and Rehabilitating Concrete Pavements Under Traffic 11 MOT Strategy and When to Use Advantages (+) and Disadvantages (-) The traditional strategy â¢ Project involves minor work â¢ Work zone is not expected to create excessive delays + Easy design + Low MOT costs â Longer overall project duration â Increased difficulty of construction â May require narrow travel lanes â May result in narrow work zones Use of existing shoulder(s) as travel lane(s) â¢ Volumes dictate that the existing number of lanes should be maintained â¢ Work is to be performed in the travel lanes + Low MOT costs + Allows for maintaining the existing number of lanes â Shoulder must be travel-worthy (traffic bearing) â May increase difficulty of construction access â No room for breakdowns to pull off Nighttime work â¢ Daytime volumes are high â¢ Work requires a restriction of turning movements that would be unacceptable during the day + Low costs (time and fuel) to motorists + Fewer impacts to peak-hour traffic/congestion â Increased labor costs â Decreased worker safety with limited visibility and impaired drivers â All work must be completed and lane closures reopened at the end of each night Weekend work â¢ Same as nighttime work â¢ Work cannot be completed in one night + Same as nighttime work â Increased labor costs â Affects travelers less familiar with alternate routes Contraflow lanes with crossover construction â¢ Long sections of pavement reconstruction/rehabilitation â¢ Work zone is not in the vicinity of ramps + Reduced conflicts between workers and vehicles + Easier construction + May reduce overall project duration â Time and cost associated with constructing and removing crossover â Difficulties arise in proximity to ramps Temporary pavementâtemporary roadway â¢ Long section of pavement â¢ No adequate detours exist â¢ Bridge work + Same as contraflow lanes â Cost of constructing roadway â Time to construct and remove temporary roadway â Inefficient use of materials Temporary pavementâwidening â¢ Volumes require that the number of lanes be maintained â¢ Project duration is expected to be long + Increases capacity through the work zone â Time and cost of widening the roadway â Inefficient use of materials Temporary structures â¢ Volumes prohibit a reduction in capacity â¢ No adequate detours exist + No reduction in roadway capacity through work zone â Time and cost of design and construction of structure â Inefficient use of materials Soft detour signing â¢ An available nearby alternate route + Reduces congestion on the mainline + Magnitude of increased congestion on alternate routes is less exists with sufficient additional capacity â¢ Work zone is expected to cause backups on the mainline â¢ Project duration is expected to be long than for hard detour signing â Unfamiliar drivers will not know the available detour routes â Increases congestion on alternate routes Table 3. Advantages and disadvantages of select MOT strategies (MDSHA 2008). (continued on next page)
12 Construction and Rehabilitation of Concrete Pavements Under Traffic MOT Strategy and When to Use Advantages (+) and Disadvantages (-) Hard detour signing â¢ Same as soft detour signing â¢ Limited number of alternate routes exist + Reduces congestion on the mainline + Provides unfamiliar drivers with a specific detour route â Increases congestion on signed alternate route Sign-only detours â¢ Work zone will reduce roadway capacity + Reduces demand through the work zone â May have low driver compliance rates One-direction detours â¢ A nearby alternate route exists with sufficient additional capacity â¢ Work is to be performed on one direction of a roadway + Same as contraflow lanes + Only half of the traffic is required to detour onto alternate routes + Fewer delay/congestion increases on alternate routes than for a full detour â Increased costs (time and fuel) to some motorists â Increased delays/congestion in one direction on alternate routes â May reduce access to some nearby businesses Full detours â¢ A nearby alternate route exists with sufficient additional capacity â¢ If such a detour would reduce overall project duration + Same as contraflow lanes + Reduced MOT costs â Increased costs (time and fuel) to motorists â Increased delays/congestion on alternate routes â May reduce access to nearby businesses â May confuse drivers Ramp closures â¢ Other ramps are nearby â¢ Alternate routes exist + Same as contraflow lanes + Reduced MOT costs â Same as full detours Reversible lanes â¢ Large variations exist between a.m. and p.m. directional volumes â¢ Number of travel lanes is limited + Accommodates fluctuations in peak traffic flow direction â May confuse drivers Movable barrier systems â¢ Need to provide for capacity during peak hours â¢ Work requires frequent barrier shifts + Provides additional work space during off-peak hours + Provides for peak flow capacity â Cost is higher than that for drums or fixed traffic barriers Table 3. (Continued). Courtesy GOMACO Corporation Inc. Figure 2. Construction of concrete pavement on U.S. 18 in Iowa using stringless paving technology with one-lane traffic in adjacent lane.
Considerations and Strategies for Constructing and Rehabilitating Concrete Pavements Under Traffic 13 frequency and duration, where possible, volume of traffic through the work zones, to increase worker and work zone safety to the greatest possible extent. An emergency response plan that includes protocols for emergency medical services should be established to deal with work zone incidents. â¢ Alternative detour routes should be established in case of unforeseen circumstances such as crashes, wide loads, and equipment breakdowns. â¢ Managing traffic in work zones is a significant component of project costs. As such, a reason- able, cost-effective strategy to reduce traffic impacts should be selected based on an evaluation of road use demands. Ways to manage costs include (1) reducing traffic volume through work zones, (2) reducing work zone frequency and duration, (3) reducing detours and crossovers, and (4) allowing multiple work zones on long projects. Larger work zones generally result in lower unit costs and schedule compression because the relative impacts of mobilization and demobilization are reduced. â¢ The contractor should be allowed to use multiple work zone setups simultaneously, and this information should be conveyed in the project plans so that the traffic control contractor can plan accordingly. The distance required between work zones should be reduced to 2 mi between flagger stations as opposed to the specified 2 mi between outermost warning signs. Paving work zones can be limited to 3.5 mi. However, the contractor should be allowed to close local road crossings in a work zone when those in adjacent zones are open to traffic. â¢ Shoulder construction and pavement marking should be completed before allowing paving of the adjacent lane or moving traffic control forward. An asphalt pavement runout can be used as a temporary transition between finished concrete pavement and unfinished milled surface or transition sections in situations with prolonged delays. â¢ The use of three-phase signal operations to control traffic through the work zone should be allowed and encouraged. A three-approach traffic signal system should be considered where bridge work and intersection reconstruction involve one common work site and paved local roads. Extended temporary barrier rails (TBRs) should be used in locations where bridges and intersection reconstruction are adjacent in order to reduce overall construction time and traffic disruption. Consider a clearance behind the TBR at bridge repair and transition construction sites of the width of pavement plus 4 ft on each side to allow for slipform paver operation. â¢ Split barricades should be placed 1 mi from the project in each direction to alert heavy equipment of road closures. Advisory signs at each end of the project should be placed to warn drivers of traffic delays. Portable signs, as opposed to post-mounted signs, should be considered within the work zones to aid in flexibility. â¢ Depending on the length of the traffic control zone, type and volume of traffic, cost consider- ations, and agency preferences, MOT plans may include flaggers only, pilot cars with flaggers, or three-phase traffic control signals. â¢ To allow through traffic at all times with reduced delays, pilot cars were operated 24 hours per day and 7 days per week (24/7) with manual traffic controls and flaggers at each end of the slipform paving work zone should be considered. Extra illumination above the flagger should be provided to improve flagger visibility and safety and to prevent vehicles from entering the fresh concrete. â¢ The centerline safety wedge, typically added to reduce crashes and crash severities associated with a vertical-edge drop-off, can be omitted where traffic is maintained in only one lane with the use of the pilot car on a 24/7 basis. Project Planning and Construction Staging Proper project planning and construction staging are necessary to reduce the risks of unfore- seen situations during construction and reduce related delays. A traffic analysis study should be conducted in the planning stages of a project to identify which parts of the roadway can be
14 Construction and Rehabilitation of Concrete Pavements Under Traffic occupied by construction and public traffic during various stages of the construction (Harrington and Fick 2014). The analysis should consider peak and off-peak traffic flows. Congestion points that could affect traffic capacity and safety as well as clearances and construction production levels should be identified. The study should be used in development of both the MOT plan and the staging and construction sequencing plan. Project plans and specifications should clearly identify agency goals and requirements for traf- fic impacts for the project (closures, number of lanes open, access, delays, safety criteria, limita- tions, number of days, work zone limits, etc.). Contractors should be provided the flexibility to propose alternatives to meet agency requirements. When planning for two-lane construction under traffic, the widths of the vehicle lane and the construction lane must be considered. Most agencies typically specify a minimum desir- able width for the vehicle lane that ranges from 10 to 11 ft. The width of the construction lane depends on concrete thickness, maximum allowable centerline drop-off or need for an edge fillet, slope of fillet, type of traffic control devices used (cones, barrels, etc.), and type of equip- ment (milling and paving) used. Traffic safety precautions, particularly when a 24/7 pilot car is not used, can include (1) treat- ing granular shoulders with calcium chloride to stabilize the shoulder and support errant vehicles, (2) installing vertical traffic control panels or a permanent safety edge to provide a visual reference indicating the pavement edge, and (3) installing a temporary safety fillet to mitigate and lessen crashes related to drop-offs between the newly placed concrete pavement and the lane where concrete has yet to be placed. Harrington and Fick provide examples of staging sequences that include detailed drawings and relevant notes for (1) two-lane roadway with paved shoulders, conventional paver; (2) two- lane roadway with granular shoulders, conventional paver; (3) two-lane roadway with mini- mum granular shoulders, zero-clearance paver; (4) two-lane roadway widened to three lanes with paved shoulders, conventional paver; and (5) four-lane roadway with paved shoulders, conventional paver (Harrington and Fick 2014). The staging sequence for a two-lane roadway with paved shoulders and conventional paver is summarized here. 1. Install traffic control and close left lane. One-lane traffic in right lane only. Repair surface, prepare for overlay, and construct base shoulder widening and separation layer, all in left lane. Can be done with short closures (less than 0.25 mi) with flaggers or signals, with or without pilot car. 2. Shift traffic control to left lane and close right lane to traffic. Repair surface, prepare for overlay, and construct base shoulder widening and separation layer, all in right lane. Con- struct right shoulder and place concrete in the right lane. Flaggers or signals with pilot car to escort traffic in the left lane may be required depending on length of the work zone. 3. Shift traffic control to right lane and close left lane to traffic. Construct left shoulder and place concrete in the left lane. Stringline may not be necessary on the right edge since the pavement completed in stage 2 can be used for paver control. Flaggers or signals with pilot car to escort traffic in the right lane may be required depending on length of the work zone. While there are many differences and similarities identified in the examples of staging sequences, a common theme is providing sufficient clearance for safe movement of traffic in an open lane while using a combination of staging, materials, equipment, construction practices, and traffic control to overcome limitations and perform construction activities in the closed adjacent lane, in some cases with very tight clearances.
Considerations and Strategies for Constructing and Rehabilitating Concrete Pavements Under Traffic 15 Strategies for Project Planning and Construction Staging Strategies for planning and staging while constructing and rehabilitating concrete pavements under traffic are discussed in the following [Cable (2012), Simon et al. (2002), and Harrington and Fick (2014)]: â¢ Agencies should apply a standardized planning approach and use comprehensive, standard tools to ensure that all aspects of planning are covered. Research has shown that organizations with a standardized front-end planning approach have better capital effectiveness. â¢ As much as practical, agencies should establish a programmatic (corridor) approach to plan- ning, design, and construction. A programmatic approach results in less disruption to traffic because it looks at an entire road corridor rather than breaking the corridor into segments that are tied to yearly funding limitations. â¢ Relocation of utilities such as telephone, electric power, and water and gas can greatly affect project delivery times. Methods should be implemented to expedite this process. â¢ When feasible, agencies should target full roadway closures rather than partial closures to increase efficiency and decrease project duration by freeing up space and reducing interference. â¢ Agencies should seek public input on the phasing of construction. Having the community more involved in highway construction projects, including choosing construction options that may allow a jurisdiction to close complete highways, can lead to faster completion. Input should be sought from local enterprises and commuters. â¢ The impact of major traffic generators along the project area should be evaluated as part of the development of MOT plans, type and extent of access to be permitted during construction, and pavement thickness design. Intersections with paved crossroads are particularly challeng- ing, and alternative overlay/inlay solutions should be considered. â¢ Construction and MOT constraints such as bridges, utilities, loop vehicle detectors, curbs, barriers, ramps, driveways, guardrails, and other structures that may affect construction should be identified, and plans to mitigate them should be developed. â¢ Construction sequencing and MOT should be planned in conjunction with joint layout, design for turn lanes, and shoulder work. For example, location and placement of longi- tudinal construction joints can affect commuter traffic through the work zone or access of construction vehicles to the job site. â¢ Replacing culverts can be time consuming and may not be needed if the existing culverts are adequate. To reduce construction project duration, routine maintenance work should be planned to be performed ahead of the construction project rather than as part of the construction project. â¢ The contractor should be encouraged to propose methods and materials for constructing temporary access ramps. â¢ Staging of construction activities can substantially affect the total amount of time that traf- fic is affected. The contractor should be provided the flexibility to establish a staging plan that meets the agency objectives for traffic impacts. Staging should be encouraged such that activities such as bridge work, transition sections, erosion control measures, edge-drain installation, patching, earth work, and shoulder/ditch work are performed prior to surface preparation and paving operations and are staged concurrent with other activities. â¢ Staging should be planned such that skilled personnel and equipment for specific construc- tion activities, such as bridge work, are available when needed. â¢ Equipment work that does not affect traffic (such as on shoulders and side ditches) should be allowed in the same area as lane closures for other prepaving work. â¢ Staging plans should allow for maximum use of slipform paving equipment to safely accelerate construction and reduce traffic impacts. The contractor should be required to develop a compre- hensive paving plan to address construction and public impacts. Transitions and bridge-approach pavement sections should be designed to keep hand placement of concrete to a minimum.
16 Construction and Rehabilitation of Concrete Pavements Under Traffic Materials and Design The materials and design used on a project affect project schedule, construction time, and the number of construction/haul vehicles, all of which can have an impact on traffic. In the 1990s, there was an emphasis on fast-track paving, where high-early-strength (HES) concrete mixtures with higher cement content were used to accelerate the setting and strength-gaining process. Fast-track paving was discussed by McGhee in NCHRP Synthesis 204: Portland Cement Concrete Resurfacing (1994), and covered in detail by Johnson et al. (1994), ACPA (1994), Ferragut (1990), and Grove et al. (1990). A concern relevant to using fast-track paving mixtures is the long-term durability and related performance issues noted on some of these projects. Advances in materials, equipment, speci- fications, testing, and construction practices in the last few decades have addressed some of the long-term performance concerns. Harrington and Fick (2014) reason that accelerated opening can often be achieved through good construction scheduling and coordination, which negate the need for fast-track mixtures. As such, durability and speed of construction are factors that should be considered together during the design phase, and whenever possible, use of conven- tional concrete mixtures should be emphasized, whereas fast-track concrete mixtures should be used only when necessary. Several lessons learned from fast-track paving projects are still pertinent to the construc- tion and rehabilitation of concrete pavements under traffic. Fast-track construction relies on monitoring material properties and uses knowledge of maturity to develop concrete strength gain characteristics and relationships for individual concrete mixes for different atmospheric conditions. In addition to achieving proper opening strength and ultimate strength, joint saw- cutting must also be accomplished at the proper time. Opening to traffic is typically based on desired concrete strength rather than time since placement. There are many factors that affect strength gain in concrete, and Johnson et al. (1994) recommend qualifying the materials and mix proportions for the specific project requirements and climatic conditions that may exist at the time of the construction. Since the 1990s, tools such as HIPERPAV, a user-friendly, Windows-based software, have been developed to assess the influence of pavement design, concrete mix design, construction methods, and environmental conditions on the early-age behavior of concrete pavements to assist with modeling strength gain and timing for saw-cutting (Ruiz et al. 2015). With fast-track paving, time is of the essence, making rapid paving operations and rapid concrete strength development critical. The HES concrete used for fast-track paving presents constructability problems, particularly because it sets very rapidly. To mitigate some of these issues, good project planning is imperative, particularly related to the sequencing of operations and the ability to rapidly place concrete once it has been mixed. Johnson et al. (1994) note that properly managing finishing and saw-cutting operations can lead to greater efficiency and allow construction work to proceed in a timely manner. On some fast-setting concrete projects constructed in the 1990s, lane closures were limited to a maximum of 48 h from the beginning of surface preparation to opening the pavement to traffic (McGhee 1994). High-Early-Strength Concrete HES concrete is concrete that achieves strength sufficient to carry loads and be opened to traffic in a matter of days, or even hours, rather than weeks. Some agencies base opening time on strength, while others specify a minimum time before opening to traffic. The required com- pressive strength at opening to traffic ranges from 1,500 to 3,500 psi and is typically 3,000 psi (Ghafoori et al. 2017). The concrete continues to gain strength after opening to traffic and can reach long-term strengths that are comparable to or greater than conventional concrete mixtures.
Considerations and Strategies for Constructing and Rehabilitating Concrete Pavements Under Traffic 17 The accelerated strength gain of HES is provided by a number of techniques, including the use of chemical admixtures, increasing the amount of Portland cement in the mixture, use of cements with finer cement grains, use of cements with higher amounts of tricalcium silicate, use of proprietary cementitious products, use of calcium fluoroaluminate cement, and use of calcium sulfoaluminate cement. Compared to conventional concrete mixtures, HES products and processes can be signifi- cantly less economical and can also have uncertain long-term performance. In many cases, costs have been reduced relative to conventional materials. The durability of these types of materials has improved, though further improvement is needed. Due to the cost and historical durability issues, HES concrete is typically used only for emergency repairs and in situations where traffic delays and closure times are a significant consideration. Roller-Compacted Concrete An option to consider for the construction and rehabilitation of concrete pavements under traffic, particularly at cross streets, is RCC. RCC is placed with conventional or high-density asphalt paving equipment and is then compacted with vibratory rollers. It has the same basic ingredients as conventional concrete, but unlike conventional concrete, it is a drier mix with essentially no slump and is stiff enough to be compacted by rollers (Zollinger 2016). RCC is quick to place and sets up quickly. As soon as RCC is down and compacted, it is capable of handling some amount of traffic. RCC can attain a compressive strength of 4,000 psi within a few days, but can be opened to traffic almost immediately. The compressive and flexural strengths of cured RCC are comparable to those of conventional concrete. Important benefits of RCC are its cost-effectiveness and ease of construction. RCC is placed without forms, reinforcing steel, or surface finishing. Dowel bars are not used at RCC joints, so RCC may not be suitable for high truck traffic applications without a mechanism to provide adequate load transfer at the sawed joints. Strategies for Materials and Design Material and design strategies to be considered for use in the construction and rehabilitation of concrete pavements under traffic are discussed in the following [Cable (2012), Simon et al. (2002), and Harrington and Fick (2014)]: â¢ Agencies are encouraged to develop a descriptive catalog of construction technologies that facilitate expedited schedules because new, time-saving construction technologies are con- stantly emerging. â¢ When necessary, all construction processes can be accelerated to minimize public impact. Contract-stage work times should be limited to emphasize the need for accelerated work. â¢ Maximize concurrent work activity with the use of modular, prefabricated components such as bridge sections and road slabs. â¢ Standard concrete mixes and maturity measurements should be used to control opening of intersections and access points. Accelerated concrete mixtures should be used only when necessary. Software such as HIPERPAV can be used to anticipate paving or curing problems and mitigate their impact on operations. â¢ Proper concrete thickness design is necessary to reduce potential issues that may arise during construction. The condition of the existing pavement may dictate surface removal or milling, which in turn may affect the design thickness. The impact on traffic due to milling or con- crete thickness should be considered. For example, thicker concrete requires more material
18 Construction and Rehabilitation of Concrete Pavements Under Traffic and, correspondingly, more trucks delivering concrete to the job site, which can potentially slow down paving operations. Pavements with substantial rutting may require additional, unplanned concrete quantities if not addressed. Intersections, geometric grade changes, and final ride quality, all of which have the potential to affect paving speed and productivity, should be taken into consideration when planning milling and concrete thickness. â¢ To make proper design decisions, agencies can review existing materials and as-built plans. Falling weight deflectometer testing and coring can be performed to identify existing pave- ment layer depths and conditions and to verify information shown on as-built plans. Review of existing distresses and field conditions can be performed to select the proper design strategy. â¢ To improve productivity and accelerate construction through a bridge area, the transition and bridge approach section widths and concrete thicknesses should be designed to encour- age maximum use of a slipform paver and to minimize hand pours. Any variable widths can be placed in the paved shoulder sections and shoulder-strengthening areas, which can be hand poured after the slipform paving is completed. â¢ If temporary shoulder-strengthening units are planned, they should be designed to be jointed with the same spacing as that of the final pavement rather than requiring them to be removed before slipform paving. Prior to slipform paving, these units can then be milled to a depth equal to the concrete thickness, and the joints on the new concrete can be matched with the joints in the milled units. ACPA and Ferragut recommended potential changes to a number of project components to shorten concrete pavement construction time (see Table 4). Project Component Possible Changes Planning Implement partnering-based project management Implement lane rental charges Allow night construction Allow contractor to use innovative equipment or procedures to expedite construction Specify more than one concrete mix for varied strength development Provide options to contractors, not step-by-step procedures Use time-of-completion incentives and disincentives Concrete materials Try different cement types (particularly Type III) Use helpful admixtures Use a uniform aggregate grading Keep water-cement-plus-pozzolan ratio below 0.43 Jointing and sealing Allow green sawing with ultralight saws Use dry-sawing blades Use step-cut blades for single-pass joint sawing Use a sealant that is unaffected by moisture or reservoir cleanliness Concrete curing and temperature Specify blanket curing to aid strength gain when beneficial Monitor concrete temperature and understand relationship of ambient, subgrade, and mix temperature to strength gain Elevate concrete temperature before placement Strength testing Use nondestructive methods to replace or supplement cylinders and beams for strength testing Use concrete maturity or pulse-velocity testing to predict strength Traffic opening criteria Revise from time to strength criteria Channel early loads away from slab edges Restrict use of automobile traffic during early-age period Table 4. Changes to project components to shorten concrete pavement construction time (ACPA 1994, Ferragut 1993).
Considerations and Strategies for Constructing and Rehabilitating Concrete Pavements Under Traffic 19 Equipment and Operations In recent years, there have been many improvements in paving equipment and placement techniques that help with various aspects of construction and rehabilitation of concrete pave- ments under traffic, including accelerating construction, reducing clearance requirements, and allowing earlier opening to traffic. As in the case of paving equipment, paving operations can also affect the extent and duration of traffic impacts, which affect decisions on closures, detours, two-lane versus one-lane paving, haul roads, and so forth. Space and traffic capacity consider- ations affect three elements of construction and rehabilitation under traffic: construction clear- ances, traffic control, and staging. Table 5 shows some considerations for the construction and rehabilitation of concrete pavements. When using a conventional slipform paver or milling machine, sufficient clearance must be provided, including for the machine tracks and frame, the stringline (which is used to control the steering of the machine), and the elevation of the finished surface. For a conventional slip- form paver, the typical clearance needed is 3 ft for the paver tracks and 1 ft for the stringline. Additional clearance may be required for cones, drums, workers, and so forth. The width of this additional clearance depends on adjacent traffic volume, traffic speed, and agency requirements. Workers on the traffic side of the operations should be limited, and in particular, workers with long-handled floats should be restricted to the side opposite traffic. When needed, with sufficient planning, paving clearances can be reduced to zero, which is sometimes termed âzero-clearance paving.â Zero-clearance paving does not include the 6 to 8 in. needed for the paving machine edge form. Equipment manufacturers have developed machines designed for minimum or zero clearance. Many contractors have made modifications to conventional equipment to achieve zero clearance. Ways to reduce clearance include using an average profiler, a movable stringline, or a ski attachment, which rely on the smoothness of an existing lane or support layer to ensure a smooth profile. Another way to reduce the clearance required is to use stringless equipment (e.g., for paving and milling). Stringless technology uses the global positioning system (GPS), robotic total Areas of Consideration Items to Consider Concrete pavement construction requirements Accelerated constructionâplanning, concrete materials, construction requirements, curing, jointing Opening to trafficâmaturity, pulse velocity, strength requirements, cure time Rehabilitation considerations Off-peak traffic hours for increased production Phasing of workâlength of work zone, project limits Special conditions such as drop-offs and sign bridge installation Prepaving and paving restrictions Special contract provisions needed Short-duration closures anticipated Temporary drainage Lights for night work Temporary roadway lighting Constructability Structural capacity of bridges, shoulders, and pavement Timing of phases versus probable starting date Strategy to allow contractor to finish project Status of existing traffic control devicesâsignals, signs, railroad crossings, etc. Wintertime restrictionsâsnow removal, etc. Table 5. Concrete pavement construction and rehabilitation considerations (Harrington and Fick 2014).
20 Construction and Rehabilitation of Concrete Pavements Under Traffic stations, and laser positioning to electronically track the equipment and control and guide the horizontal and vertical operations of the equipment. Stringless systems increase productivity and reduce costs through reducing the need for sur- veys and eliminating the labor involved in setting, maintaining, and removing the stringline. While stringless systems require surveys to establish the project reference points, they eliminate the need to place paving reference hubs or pins at regular (12- to 50-ft) intervals. Another advan- tage of using stringless systems is greatly improved work zone access for construction and other vehiclesâand safety for workers and pedestriansâthrough eliminating detour needs as well as tripping hazards caused by the stringline. Those living, working, or visiting near the construc- tion site can enter and leave residences or businesses without concern of stringline interference. One method to improve the productivity and efficiency of paving operations is through the use of static or mobile three-dimensional (3D) laser scanning surveys. Compared with conven- tional survey methods for pavement surface mapping that use a total station, rod, and level; a GPS rover unit; or vertical (looking down) sonic units, 3D laser scanning equipment can collect large amounts of survey data (high-definition survey) quickly, reliably, and accurately in a cost- effective manner, with less traffic disruptions during survey operations. Information from these scans can be integrated into stringless paving operations. Strategies for Equipment and Operations Cable (2012), Simon et al. (2002), and Harrington and Fick (2014) provide several paving equipment and operations strategies to be considered for use in constructing and rehabilitating concrete pavements under traffic. The strategies are summarized here: â¢ Efficiency in construction operations should be encouraged. The contractor should be required to develop a plan that meets both project and contractor needs. The plan should take into consideration efficiency in operations and use of people and equipment, the concrete delivery plan, material source locations and access to the plant, access from shoulder material sources to the completed work areas, public travel disruption, and local crossing access. The contractor plan should be evaluated on its ability to deliver the completed project in the least amount of time and with the least amount of interference with the traveling and local public. â¢ When the project is constructed with a single lane under pilot-car and flagger traffic control, additional haul-road designations should be allowed, and local compensation should be pro- vided for raw material and concrete delivery throughout the project. â¢ Exceptions from plans and specifications should be allowed if the contractor can demonstrate reduction in traffic impacts. For example, allow one subcontractor crew to work within the same work zone as other subcontractor or contractor crew (edge-drain installation, patching, bridge/transition paving) on either side of the roadway, even across the road from a lane clo- sure, when it can be performed safely and work equipment does not encroach on the traveled way. This allowance helps with faster completion of shorter tasks that may be in the critical path of longer (e.g., paving) tasks, thus reducing delays in the longer tasks. â¢ Allow exceptions to maximum work zone length on a case-by-case basis to improve efficiency, rather than requiring setup and removal of additional work zones at multiple locations. Allow exceptions to reduce the total number of work zones that may be required on a given project where multiple subcontractors are working at the same time. â¢ Allow for more than one paving work zone at a time to make efficient use of contractor resources and time. Multiple work zones for patching-type work enable the contractor to prepare patch areas by sawing in a second zone while removal and replacement is taking place in the first zone.
Considerations and Strategies for Constructing and Rehabilitating Concrete Pavements Under Traffic 21 â¢ For work that may affect schedule and traffic, consider permitting use of a moving traf- fic control operation of a given distance. To reduce slowdowns at bridge approaches and transitions, the layout of the new bridge approach and transition concrete should be done in conjunction with that of the pavement gradeline. â¢ Traffic should be allowed on concrete patches as soon as practical. Allow opening 1 h before dark rather than at the end of the workday, or allow when the estimated flexural strength of the patch reaches 350 psi. Calcium chloride in concrete patch mixes should only be used when air and pavement temperatures do not support sufficient strength gain in the time between placement and opening to traffic. â¢ Maturity testing allows an engineer or manager to monitor concrete strength gain. Maturity meters can be used at the beginning, middle, and end of the dayâs patches. The maturity recording devices should be able to record continuous values to aid the contractor in poor weather conditions and provide a more accurate record in cases of dispute over joint devel- opment and opening times. Maturity measurements can also be used as trigger values for sawing in hot weather conditions where concrete placed in the early morning, at noon, and late in the evening cures at different rates. When forms are used, maturity meters can be used to strip forms sooner and so they can be reused more frequently, resulting in efficiency and time savings. â¢ The use of automated technologies for paving, milling, compacting, and queue control for haul vehicles, such as GPS, laser-based positioning systems, and robotic equipment controls linked to 3D designs, should be encouraged. These can result in higher-quality construction operations with reduced delays. â¢ The number of gaps in the closures (e.g., for intersections and driveways) should be mini- mized to provide for uninterrupted paving, increased productivity, reduced project time, and reduced overall traffic impacts. For example, a single temporary access can be provided to adjacent property owners where possible, or other ways to accommodate the daily needs of affected properties can be established. â¢ Leaving gaps in or staggering construction areas can allow the contractor to stage work more efficiently by optimizing resources such as crew and equipment and even using multiple pavers. Proper sequencing of paving operations is important to make sure that the paver ends each area in the optimum position to begin work in the next area. â¢ For each project, the lane closure criteria should be clearly established by the agency. The contractor should be allowed to suggest various alternatives to meet the criteria. Project Management, Delivery, Procurement, and Payment Proper planning and management of a construction project are necessary to ensure that the project proceeds as planned and is completed on time and within budget while meeting agency goals for quality, safety, and traffic impacts. The contracting and procurement phase is an important part of expediting construction and achieving quality. Procurement practices can be tailored to balance agency goals for costs, project duration, quality, traffic impacts, and other factors. Project delivery is another factor that has a bearing on construction projects in terms of how they are managed and executed. It has a direct impact on the speed of the decision-making process and the schedule for project completion, which in turn can affect the extent to which traffic is affected. Various forms of incentive/disincentive (I/D) provisions are also effective tools that can be used by an agency to accelerate construction and reduce delays and corre- sponding traffic impacts.
22 Construction and Rehabilitation of Concrete Pavements Under Traffic Strategies for Project Management, Delivery, Procurement, and Payment The following list, summarized from Simon et al. (2002), includes a number of project man- agement, project delivery, project procurement, and payment method strategies to be consid- ered for expediting highway construction: â¢ A single individual should be designated as the project manager (PM), from initiation to construction, to maintain continuity throughout the project. The PM should be equipped with the needed tools and data to select appropriate expediting methods and be empowered to make their selection. â¢ Agencies should consider using the linear scheduling method (LSM), with accurate produc- tivity rate data, to establish project target duration. LSM allows an activity to be modeled as a line with dimensions of time and location, unlike traditional scheduling methods that model linear activities as having constant production rates. â¢ Agencies should consider the use of e-commerce systems to improve document management and communication, which may improve project speed. â¢ Tools and best practices for implementing multiple work shifts or night work should be devel- oped. Attention should be paid to safety and implementing night MOT plans. Multiple work shifts can lead to improved project speed. â¢ Agencies should develop a change management plan that encompasses strategies and tech- niques to manage change within the project. The plan should identify how changes will be handled, who should be informed, and alternatives to changes (if any). The plan should record the effect of the change on the overall project, including the schedule. The change manage- ment plan will help ensure that changes are handled in a timely manner. â¢ On large projects, agencies can consider creating a project-level dispute review board (DRB). A DRB is a standing committee appointed at the start of a project to hear disputes. The board convenes at the request of either party or at a certain frequency and is informed of progress. It issues nonbinding decisions related to disputes that can help the parties resolve issues at the project level in a timely manner. â¢ Agencies can consider alternatives to litigation for dispute resolution, such as negotiation, mediation, summary jury, and arbitration, which have proven to be successful in quickly resolving disputes. â¢ Agencies can consider the use of windowed milestones, which are milestones with float within a window. Windowed milestones may provide more flexibility in scheduling and lead to improved project speed as compared to traditional milestones, which can artificially con- strain a schedule. â¢ Project schedule performance can be measured and tracked for use as the basis for an employee reward program, as well as for input to the project duration database. Agency and contractor employee incentives and compensation can be tied to project schedule performance through annual evaluations or direct incentive programs. This may result in faster delivery schedules. â¢ Incentive-based pay can be used to retain key personnel, which can be critical to overall proj- ect time performance. The performance of project teams is enhanced substantially with expe- rienced and skilled personnel. â¢ Duration and productivity effects associated with different technologies should be tracked. Having a duration and productivity database associated with different technologies can be useful in deciding on, suggesting, and incentivizing the best technologies to use on future projects. This database can also be used in qualification-based bidding and in best-value bid awards. â¢ Pilot demonstration projects can be used to introduce new methods for expediting schedules and aiding the transition process. Application to smaller projects and concentrated attention minimize the risk associated with the new approach.
Considerations and Strategies for Constructing and Rehabilitating Concrete Pavements Under Traffic 23 â¢ Agencies can consider developing a database of activity productivity rates of different con- struction methods and lessons learned on ways to expedite schedules. This can be used to decide which methods to use on future projects and to provide schedules with more realistic targets. â¢ Agencies can consider developing optimal approaches to crew shifts and scheduling so that overly long work weeks or night work do not reduce productivity and the rate of progress. â¢ Field personnel can be trained in scheduling methods and schedule claims. Having trained personnel who can assess schedule impacts and make good decisions can help expedite sched- ule performance and lead to more effective and realistic time estimates. â¢ Designâbuild (DB) approaches in various forms, such as designâbuildâwarrant (DBW), which combines a warranty provision with DB, and designâbuildâmaintain (DBM), which combines maintenance provisions with DB, can be considered as alternatives to the traditional designâbidâbuild (DBB) system. In DB, the design and construction duties are performed by the same contractor. Other options include privatization or publicâprivate partnership (PPP), where a private entity designs, builds, and maintains a section of roadway in return for a toll or fee. These alternatives can improve efficiencies and reduce construction time, thus reducing traffic impacts. â¢ Formal partnering with design consultants, contractors, local authorities, and regulatory agencies, in which all parties to a project voluntarily agree at the outset to adopt a cooperative, team-based approach to project development and problem resolution, can be considered. Partnering can result in reduced agency response times, thus reducing overall construction time and traffic impacts. â¢ The MOT plan developed by the contractor should be incentivized with a value engineering (VE) cost-savings sharing clause in the contract, with special emphasis on time-saving or duration-reducing practices on MOT plans. â¢ A+B bidding (also called cost-plus-time bidding) can be used in the procurement phase to factor into the selection process the time to complete the project while considering the lowest initial cost. This effectively provides contractors I/D based on project duration. â¢ For projects where significant traffic impacts are anticipated, agencies can consider prequali- fying bidders on the basis of past schedule performance to eliminate those with a poor record of schedule performance. â¢ An option to consider is the use of contractor incentives for meeting specific milestones in which contractors are financially rewarded for on-time delivery of specific work tasks or deliv- ering products. â¢ A lane rental approach, where the contractor is assessed daily or hourly rental fees for each lane, shoulder, or combination of the two taken out of service during a project, is another disincentive option for late completion that can minimize the time that roadway restrictions affect traffic flow. â¢ Agencies can consider provisions in the contract for liquidated damages, allowing the agency to reduce payment to the contractor by a predetermined amount for each delayed time unit (hours or days). Liquidated damages can be used in conjunction with incentives to improve project speed. â¢ Agencies can also consider no-excuse incentives, in which the contractor is given a firm deliv- ery date, with no excuses allowed for missing that date. Incentives are provided for early completion; however, there are no disincentives other than normal liquidated damages. Communications and Outreach Project-related communication within an agency and between various stakeholders are crucial for smooth and timely execution of construction and rehabilitation of concrete pave- ments under traffic. Communication of construction activities with the traveling public,
24 Construction and Rehabilitation of Concrete Pavements Under Traffic local residents and businesses, and other affected parties and agencies is paramount to reducing and mitigating their effects. A well-planned and well-executed public outreach program can be an effective tool to help reduce the extent and severity of traffic impacts. As in the case of public outreach, conveying timely information to motorists about the affected roadway is critical for reducing traffic impacts. Table 6 shows some communication and outreach considerations for the construction and rehabilitation of concrete pavements. Strategies for Communications and Outreach The following list includes communication and outreach strategies to be considered for use in constructing and rehabilitating concrete pavements under traffic [Cable (2012), Simon et al. (2002), and Harrington and Fick (2014)]: â¢ A preconstruction meeting that is open to the public should be held to communicate traffic control impacts and solicit public concerns. To the greatest extent possible, these concerns should be addressed or mitigated during construction. A public meeting before fieldwork commences allows the public to interact with agency and contractor staff. The meeting can be used as an opportunity for the contractor to present the schedule of construction events and identify potential local conflicts, thus allowing time to develop plans for averting the conflicts. The meeting can alert the public to expected delays and closures so that they can better plan travel and activities that intersect with the project area. â¢ Communication within the highway agencyâs design and construction staff during design and prior to construction can reduce potential delays during construction. For example, the deci- sion about when and what to do in the way of surface preparation should be made in the design phase to reduce potential issues that may arise during the construction phase. Surface preparation can be modified in the construction phase if the assumptions used in the con- crete thickness design are communicated between the design and field office staff. Timely decisions, for example on contractor questions, should be made by agency staff to allow the contractor to perform work without delays. â¢ A proactive, partnership approach between all stakeholders should be used to reduce traffic disruption in work zones. Engagement of local officials, businesses, and the public early in the development process can give planners a better understanding of traffic-related issues that could arise on the project and help them plan accordingly to develop better and coordinated solutions. Early public engagement also helps roadway users plan travel routes and times to account for work zone detours and delays. â¢ A variety of evolving technologies that offer new solutions that help improve transportation conditions based on electronic technologies, communications, information processing, and navigation technologies are revolutionizing the interfaces between the driver, vehicle, and roadway to control traffic, thus facilitating more efficient construction. Area of Consideration Items to Consider Public information coordination Public informationâpublic hearings, media, motorist service agencies, residents, local businesses, motor carriers Local officialsâpolice, fire, hospitals, schools, environmental agencies, utilities, toll facilities, ferries, railroads, airports Special events Intra-agency coordinationâmaintenance crews, permits section, adjacent projects Transit Table 6. Communication and outreach considerations for the construction and rehabilitation of concrete pavements under traffic (Harrington and Fick 2014).
Considerations and Strategies for Constructing and Rehabilitating Concrete Pavements Under Traffic 25 â¢ A web-based team-collaboration system for communications through all phases of the proj- ect should be used. Web-based systems eliminate any apparent boundary between a project participantâs computer and the projectâs folders and files. They can be as simple as a common e-Room or as complex as web-based central project databases, business-to-business capabilities, and intelligent software agents. Improving communication may speed the construction process. Summary of Concrete Construction Under Traffic Table 7 provides a summary of various factors to consider when constructing concrete over- lays under traffic. Factors to Consider Note Incentives/disincentives I/D can be used to encourage the contractor to perform ahead of or within a given schedule, particularly in a competitive bidding environment. Grade control The elevation of the concrete paver can be controlled by a traveling ski, a stringline, or through stringless technologies. Regardless of the mechanism, reference points are needed to establish proper grade of the final pavement. Proper grade control is essential for smooth pavement and can also affect paving productivity. Reliability of material supply To avoid unnecessary project delays, all materials that are required on the project need to be made available when needed through properly scheduling delivery or being stockpiled nearby prior to construction. Material schedule Representative samples of all material supplies should be made, with proper certification, to avoid interruptions and slowdowns during construction. Concrete mixture The mixture needs to match the opening requirements and construction methods. Conventional mixtures should be used as much as possible to reduce durability failure risks. Accelerated mixtures should be used only when appropriate or needed for early openings. The mixture should not be accelerated to a point where there is a high probability of early-age cracking from shrinkage and curling and warping. Cementitious materials Cementitious materials such as Type I cement, Type II cement, and cement blends with supplemental cementitious materials such as fly ash and slag should be chosen depending on the strength gains needs for the project. Multiple options may need to be selected within the same project, depending on opening requirements and other considerations. Chemical admixtures Chemical admixtures such as water reducers, accelerators, air entrainment agents, and retarders may be used to meet the project needs of rapid strength gain, workability, durability, and so forth. Acceptance tests should be conducted with job materials under anticipated conditions. Compatibility of the admixtures with other ingredients should be tested since this is related to potential constructability problems. Aggregates Aggregates that are well graded have less space between aggregate particles, therefore reducing paste demand without loss of workability; poor workability can affect the quality and productivity of paving operations. Separator layer When overlaying existing pavements, a separator layer can reduce the need for extensive repairs to the existing pavement prior to overlay, thus reducing project duration and traffic impacts. It also provides a uniform platform for paving equipment, which can affect smoothness and paving productivity. Table 7. Considerations for concrete construction under traffic (adapted from Harrington and Fick 2014). (continued on next page)
26 Construction and Rehabilitation of Concrete Pavements Under Traffic Factors to Consider Note Drainage If drainage improvements affect the construction schedule, they should be conducted under a separate project and completed during off-peak hours or in coordination with other closures. Utilities As with drainage improvements, all utility work should be completed prior to the overlay in order to reduce interference or early-age damage. Surface preparation/cleaning The equipment used for surface preparation and cleaning should be sized to not only provide adequate production rates but also to reduce disruption to traffic and to assist with the accelerated schedule. Traffic on prepared surface Phasing of the surface preparation operation can allow for intermediate trafficking of the surface prior to the overlay placement. Vehicle access Vehicle access should meet the needs of roadway users. Because of different strength requirements, agencies may consider opening pavement to cars earlier and to trucks later. Pedestrian access in intersections/urban areas Pedestrian movements should be channeled around the construction zone. Detouring the pedestrian path may be necessary. Traffic control devices Traffic control should be fitted to meet user needs and follow the Manual on Uniform Traffic Control Devices. Due to advancements in construction equipment and processes, the limitation of clearance requirements for paver tracks and stringline are no longer valid, and many options are now available. Lighting Lighting allows night work and must be mobile to move with the construction activities. Nighttime construction Nighttime construction provides an off-peak construction period that lessens disruption to traffic. Nighttime visual limits should be used. These include shorter spacing of channelizing devices, longer transitions, changing colors nearing off-ramps, widening pavement markings, using glare screens, using more truck-mounted attenuators, using real-time information on signs and changeable message signs, and covering signs when work is not being done. Lane capacity Lane capacity is a function of the construction zone speed and not the roadway design speed. It must deal with existing traffic flows in a safe manner for both the driver and construction worker. Batching Depending on the size of the job, a dedicated mobile batch plant can benefit the project. Regardless of the source of concrete mixture, adequate batching capacity, in terms of mixing time, production volume, and transport equipment, is crucial to prevent any slowdowns in paving operations. Concrete transportation: traffic separation To prevent any slowdowns in paving operations, appropriate measures should be taken to ensure continuous, uninterrupted delivery of concrete. Concrete transportation: transit time If there is a potential for extended transit times due to traffic congestion or long travel time, a modified mixture with a retarder may be necessary. Caution must be exercised using a retarder as it may also affect the strength gain of the mixture, thus affecting the time of opening to traffic and curing needs. Haul roads Evaluation of a haul road in questionable areas should be done prior to the first batching to avoid any delays associated with damages to the haul roads. Pre-overlay repairs If pre-overlay repairs affect the construction schedule, they should be conducted under a separate project, completed during off-peak hours or in coordination with other closures. The equipment used for repair should be sized to not only provide adequate production rates but also to reduce disruption to traffic. Table 7. (Continued).
Considerations and Strategies for Constructing and Rehabilitating Concrete Pavements Under Traffic 27 Factors to Consider Note Events Work zone management plans should take into consideration special events. Coordination with appropriate authorities and stakeholders may be necessary to ensure the least amount of disruption. Visibility Visibility is a consideration when planning equipment and traffic control. Adequate stopping distance at work zones must be provided. Staging area Having the staging area close to the job site is beneficial to productivity and reduced delays. A mobile batch plant located near the project site cuts down on the haul times to the site, and the quality of the mixture will also be more easily controlled. Incremental lane closure (leap frog) Incremental lane closure increases productivity by allowing for continuous, single-lane paving in one direction, leaving opened areas for traffic recovery. However, it requires multiple traffic control setups and pilot cars. Mobilization The project should be planned to reduce staging operations and mobilizations. Remobilizing of the paving crew at the end of each stage on to the next stage takes time, reduces productivity, and increases costs. Work production To increase productivity and reduce delays, construction crews should be utilized effectively by using work schedules that provide continuous and uninterrupted efforts. Number and type of lane closures The number and type of closures depend on traffic demands, lane capacity, access requirements, and number of available traffic lanes. Construction under traffic versus lane closure A costâbenefit analysis should be performed, and various alternatives, such as full closure versus maintaining traffic through the construction zone, should be considered. Thickness of pavement Pavement thickness can affect productivity as thicker pavements require more concrete to be delivered to the job site for the same rate of paving. Early sawing is needed for thinner pavements because they cure quicker. Weather Consider covering the pavement to help achieve opening strength during cold weather. Faster strength gains can happen during hot weather, along with an increased risk of early-age cracking. Proper curing is essential to reduce these risks. Construction equipment An important aspect of accelerated construction is the availability and performance of construction equipment. To avoid stoppages or slowdowns, all equipment should be readily available, in working condition, and properly maintained. A backup plan in the event of equipment failure during construction should be established. Spare parts, hydraulic fluids, oil, fuel, and so forth should be readily available. Curing For concrete that requires a very short opening to traffic, insulating blankets, in addition to a curing compound, can be used. Insulating blankets are not normally needed in summer months for accelerated construction but may be needed during the colder months. Sawing Saw-cutting timing should balance the potential for uncontrolled cracking with the potential for excessive joint spalling during sawing. Programs such as HIPERPAV can be used to establish optimal windows for saw-cutting. Fillets Edge fillets may be needed as a safety precaution when there is an elevation difference between a newly paved lane and the lane that is yet to be paved. Fillets may require sawing before paving the unpaved lane. Large trucks Special attention should be given to accommodate large trucks in work zones and transitions, particularly where truck volume is high. Items to consider include lane widths in curves with runs of barriers on both sides and stopping distance where congestion is expected. Detours Detours must be conveniently located and have effective signage. Long detours should be avoided when possible. Table 7. (Continued). (continued on next page)
28 Construction and Rehabilitation of Concrete Pavements Under Traffic Factors to Consider Note Schedule A realistic project schedule should be established. Proper equipment and staffing, mixtures, construction methods, curing, and sawing are all considerations when establishing the schedule. Traffic controls and openings, staging, material requirements, and many other factors can affect the construction schedule. Maturity method Using maturity testing for concrete paving provides a reliable technique for estimating in-place strength and thus the time of opening. Maturity testing enables a pavement to be opened to traffic as soon as it meets strength criteria established by the agency. Public relations An effective public relations campaign should be implemented where construction will affect homeowners, businesses, and the traveling public. This includes flyers, media coverage, and public meetings. Preconstruction meetings can be used to keep the public informed, solicit feedback, and address concerns. A strict schedule should be followed and conveyed to the appropriate businesses, households, and so forth. Proper signing to business access is important, along with daily communication between the contractor and the affected businesses. Informed local drivers can avoid the area when possible, thus reducing delays. Table 7. (Continued).