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1Types of Composite Pavement Systems Two composite pavement design strategies were determined to provide both excellent surface characteristics (low noise, very smooth, nonpolishing aggregates, and durability) that can be rapidly renewed, and long-lasting structural capacity for any level of truck traffic. These two composite pavement design strategies were determined to reflect the Strategic Highway Research Program 2 (SHRP 2) Renewal philosophy of âget in, get out, stay out.â ⢠High-quality, relatively thin, hot mixed asphalt (HMA) surfacingâsuch as dense HMA, stone matrix asphalt (SMA), porous HMA, asphalt rubber friction course (ARFC), or Novachip gap-graded asphalt rubber hot mixâover a new portland cement concrete (PCC) struc- tural layerâsuch as jointed plain concrete (JPC), continuously reinforced concrete (CRC), joined roller compacted concrete (RCC), or a lean concrete base/cement-treated base (LCB/CTB). ⢠High-quality, relatively thin PCC surfacing atop a thicker, structural PCC layer. Both types of composite pavements have strong technical, economical, and sustainable merit in fulfilling the key goals of the SHRP 2 program, including long lived pavements, rapid renewal, and sustainable pavements. A survey of U.S. and international highway agencies conducted under the SHRP 2 R21 project revealed considerable interest in both HMA/PCC and PCC/PCC composite pavements. Research Objectives The objectives of this research were to investigate the design and construction of new composite pavement systems. The previous technology for the design and construction of new composite pavements was limited. The structural and functional performances of these composite pave- ments were not well understood or documented. There were no existing mechanistic-empirical (M-E) performance models of these pavement systems, and they need to be developed or improved for use in design, pavement management, and life-cycle cost analysis (LCCA). In addition, the current construction techniques, guidelines, and specifications were insufficient to construct composite pavements properly. These types of composite pavements give significant flexibility to the designer to optimize the pavement design in terms of life-cycle costs, reduction in future lane closures, and improved sustainability. They essentially exhibit the advantages of conventional HMA and PCC pavements Executive Summary
2while minimizing their disadvantages. The research under this study, which was conducted from 2007 to 2011, accomplished the following key goals. ⢠Objective 1. Determine the behavior, material properties, design factors, and performance parameters for each type of composite pavement. ⢠Objective 2. Develop and validate M-Eâbased performance prediction models and design pro- cedures that are consistent with the Mechanistic-Empirical Pavement Design Guide (MEPDG). ⢠Objective 3. Develop recommendations for construction specifications, techniques, and quality management procedures for adoption by the transportation community. Constructed and Field Survey Sections Experimental composite pavements were constructed at two major research sites (MnROAD, Minnesota and the University of California Pavement Research Center [UCPRC] at Davis) and were instrumented and monitored under actual climate conditions and heavy traffic loadings. An HMA/JPC composite pavement also was constructed by the Illinois Tollway north of Chicago. Extensive field surveys were performed in the United States, Canada, and Europe of 64 sections of the two types of composite pavements and used in the analysis and validation. MnROAD/Minnesota Department of Transportation One of the major research sites was set up by MnROAD in Minnesota. ⢠Design and materials: Three sections were constructed. The top layer PCC mix contained increased cement content and a high-quality, very durable aggregate (granite). The aggregate in the top lift was gap-graded and had a maximum size of 0.5 in. (12.7 mm). All basic com- ponents of the lower-layer PCC were selected to reduce costs, investigate methods of sustain- ability, and investigate the reuse of materials into structural components. Higher traffic in the outside lane and lower traffic in the inside lane provided two levels of traffic. JPC was the basic type of pavement with transverse joints at 15 ft and dowels at all PCC/JPC joints and in the travel lane only for HMA/JPC joints. 4 Cell 70: This section was 3 in. of HMA over 6 in. of JPC (50% recycled concrete aggregate [RCA]; 40% fly ash replacement) over an unbound aggregate base course. The inner lane transverse joints included no dowels, but the outer lane included dowels. Transverse joints across both lanes were sawed and sealed for reflection crack control. 4 Cell 71: This section consisted of a 3-in. high-quality PCC layer over a 6-in. low-cost PCC layer (50% RCA; 40% fly ash replacement). 4 Cell 72: This section consisted of a 3-in. high-quality PCC layer over a 6-in. PCC layer with 60% fly ash replacement and inexpensive coarse aggregates. 4 Texturing of Cells 71 and 72: (1) Exposed aggregate concrete (EAC) achieved by brushing the surface, (2) conventional diamond grinding, and (3) ultradiamond grinding. ⢠Specification development: Full specifications for bidding were developed for each type of composite pavement. ⢠Instrumentation and data acquisition: Instrumentation installed in the pavements included thermocouples for measuring temperature throughout the pavement structure and humid- ity sensors to measure concrete moisture (relative humidity) levels within the slab. Static strain for static loads generated was measured with vibrating wire (VW) strain gauges to provide several critical pieces of information related to the performance of the pavement layers, responses to temperature and moisture changes, slab curvature, and in-place drying shrinkage. Dynamic strain sensors to measure the slab response to loads applied by truck traffic and the falling weight deflectometer (FWD) were also installed. All data were stored at the MnROAD facility.
3 ⢠Construction: An initial 200-ft test section for PCC/PCC was built and the EAC surfaced pre- pared. The lessons learned were invaluable for building the main line, which was constructed in May 2010. Construction went well with no serious problems. ⢠Loading and monitoring: Pavements were opened to I-94 traffic in July 2010 and have been loaded ever since except for short closures for monitoring. A full year of heavy traffic has been achieved and the findings included in this report. University of California at Davis Pavement Research Center The other major research site was set up by the Pavement Research Center at the University of California at Davis. ⢠Design: The composite HMA/JPC pavement has four 12-ft-wide lanes to accommodate two HMA mixtures, with two HMA thicknesses, two PCC thicknesses, and PCC with and without dowels for load transfer. Each lane has three sections, each consisting of three slabs of 15-ft length. Each pass of the Heavy Vehicle Simulator (HVS) covered two transverse joints and one 15-ft slab in each section. ⢠Specification development: California State specifications were used for construction with some additional requirements. ⢠Instrumentation: Joint deflection measurement devices were installed to measure absolute vertical movement of PCC slab joints, from which the relative movement of the two slabs on each side of the joint can also be measured. Horizontal joint deflection measurement devices were used to measure relative horizontal joint movement caused by the opening and closing of PCC slab joints. Thermocouples and moisture sensors were installed to measure PCC and HMA temperature and relative humidity at various depths. Dynamic strain gauges were placed at slab corners and centers and between HMA lifts in the thicker HMA layers to measure strains occurring under the moving HVS wheel. Static strain gauges were installed to measure slowly changing PCC strains at the top and bottom of the slab caused by creep, shrinkage, warping, and curling. ⢠Construction: PCC was placed in August 2009, and the HMA was placed shortly thereafter. The PCC and two types of HMA both met their respective California Department of Trans- portation (Caltrans) paving specifications. An anionic SS-1h emulsion tack coat was applied. On Lanes A and B, the mix placed was a ¾-in. (19-mm) maximum aggregate size, dense graded mix with polymer modified PG 64-28 binder (PG64-28PM). On Lanes C and D, the mix placed was a ½-in. (12.5-mm) maximum aggregate size mix with gap-graded aggregate and an asphalt rubber binder produced using the âwet processâ (RHMA-G). ⢠Loading and monitoring: The HVS was used to load and evaluate the pavement for HMA rutting, joint reflection cracking, and PCC slab fatigue cracking. The slab cracking loadings required 200,000 and 320,000 heavy wheel repetitions to be applied on two 5-in.-thick non- doweled slabs with thin and thick HMA, respectively. Additional cracking tests may be per- formed after the R21 project using other funding. Illinois Tollway There was also a research site set up in Illinois. ⢠HMA/JPC composite sections were constructed near Gurnee, Illinois, on the ramps from I-94 to Milwaukee Avenue (off-ramp in the eastbound direction and on-ramp in the westbound direction). The ramps were constructed in October and November 2010 to emulate best practices of constructing HMA/JPC composite pavements using recycled aggregate in the PCC slab. ⢠The project consisted of using stockpiled recycled asphalt pavement (RAP) coarse aggregate in the PCC mix with a warm mix asphalt (WMA) surface layer. The relatively thin (2-in. [50-mm]),
4high-quality dense-graded WMA layer was placed and bonded to the newly placed 9-in. (225-mm), low-cost PCC lower lift after the PCC had hardened sufficiently. ⢠The PCC slab included a partial replacement of cement with fly ash (~20 to 25%). The use of RAP and fly ash offers environmental advantages by diverting the material from the waste stream, reducing the energy investment in processing virgin materials, conserving virgin materials, and minimizing pollution. ⢠For WMA, the mix is heated to a lower temperature than for conventional HMA (~60°F to 90°F reduction). Lower temperatures mean less fuel consumption, lower stack emissions, and less fume and odor generation at the plant and job site. ⢠Coarse aggregate fractionated from the RAP made up 30% of the total coarse aggregate in the PCC mix. Aggregate fines less than 4.75 mm (No. 4) used in the PCC mix were specified to come from virgin aggregate sources. RAP was fractionated, cleaned, and washed. As much as 15% of the total recycled coarse aggregate could consist of agglomerated sand/asphalt particles. ⢠The PCC surface was cured and textured after placement to ensure adequate bond with the HMA layer. A tack coat was sprayed on to ensure bond. The transverse joints were sawed and sealed in the HMA layer over the joints in the JPC. Field Surveys of In-Place Composite Pavement Sections Data were gathered from field surveys of in-place composite pavement sections. A variety of HMA/PCC composite pavement structures were identified: ⢠Thin asphaltic surfaces, including dense HMA, porous HMA, SMA, ARFC, Novachip, and WMA; and ⢠Concrete lower layers including JPC, CRC, jointed RCC, jointed LCB, and jointed CTB. A variety of PCC/PCC composite pavement structures were identified: ⢠High-quality thin concrete surfaces, including EAC, higher strength PCC, and diamond- ground PCC; and ⢠Concrete lower layers, including JPC (some with recycled concrete, regular concrete, and lower cost concrete) and CRC. European countries have been constructing HMA/PCC and PCC/PCC composite pavements for several decades and have substantial experience. HMA/PCC composite pavement was evalu- ated in the Netherlands using porous 2- to 3-in. HMA/CRC on more than a dozen major heavily trafficked projects, all of which exhibit low noise levels, no rutting, and no reflection cracking. Germany has built SMA surfaces on JPC and most recently over CRC. One SMA/JPC section was 15 years old under heavy traffic with sawed and sealed joints that had performed very well. Austria, Germany, and the Netherlands have all constructed many projects with 2- to 3-in. EAC PCC/JPC since the late 1980s. The entire 200 miles of the A1 freeway across Austria is of this design, with the lower layer PCC containing recycled concrete and about 10% RAP. This highway lies in the harsh climate of the Alps with lots of snow and ice. None of these sections exhibited significant problems and have performed very well over 20 years. In reviewing these case studies and discussing the composite pavements with the host engi- neers and practitioners, numerous benefits to importing and implementing European tech- niques were identified. Dutch, German, and Austrian researchers say that composite pavements provide similar structural performance as an equivalently thick single layer at the same price in Europe, yet the road surface has higher quality and longer life and friction and noise reduction because of the high-quality top layer. Furthermore, composite pavements allow for the optimiza- tion of costs and materials throughout the pavement cross section: ⢠High-quality materials can be used in lesser quantities in the upper layer, where they will be of the most benefit to the system; and
5 ⢠Less expensive materials can be used in greater quantities in the lower layer, where they will con- tribute structurally without detracting from the quality and performance of the overall pavement. Studies in Spain provided valuable information on reflection cracking for HMA/RCC and HMA/CTB and the forming of joints in the RCC and CTB. Since 1991, Spain has used the wet- forming process to form joints. Long-term results show the effectiveness of wet-formed joints every 8 to 13 ft in terms of a reduction in joint deflections and high values of joint load transfer efficiency. The studies also showed that short joint spacing led to fewer reflection cracks, tighter cracks, and improved performance. Composite Pavement Design The design procedures in DARWin-ME for HMA overlay of jointed plain concrete pavement (JPCP) and continuously reinforced concrete pavement (CRCP) and in the MEPDG for bonded PCC overlay of JPCP and CRCP were found to be the most comprehensive and applicable for design of new composite pavements. Through use of appropriate inputs, the overlay procedure could be used for new composite pavement construction. Extensive testing and evaluations were performed, and many bugs related to composite pavements, as well as significant improvements, were identified and fixed in the MEPDG. A new version of the MEPDG (v. 1.3000:R21) was devel- oped to use the Bonded-PCC-over-JPCP project to simulate newly constructed PCC/PCC and address limitations of the existing structural and environmental models for PCC/PCC. CalME The UCPRC has been developing an M-E pavement design method for Caltrans. The associ- ated software is called CalME. CalME rutting and reflection cracking models were evaluated for the SHRP 2 R21 project. The rutting models were calibrated using the results of the HVS and MnROAD test sections, whereas the reflection cracking model was tested using the results of some of the HVS test sections. Although the number of test cells used in the calibration was small, the results show that the CalME models can predict measured performance effectively using average calibration coefficient values. A sensitivity analysis was performed to evaluate the effects of climate, traffic, HMA mix type, aggregate base stiffness, crack spacing, and HMA thick- ness. The sensitivity analysis showed that HMA mix type is the primary factor that affects both rutting and reflection cracking. NCHRP Report 669 Reflection Cracking In National Cooperative Highway Research Program (NCHRP) Report 669, a reflection cracking model was developed specifically to be implemented in the MEPDG and DARWin-ME. The pro- cedure was reviewed, tested, and recommended for implementation in DARWin-ME. It appears that this approach and model will reasonably predict transverse joint reflection cracking for HMA/JPC composite pavements. The existing empirical reflection cracking model was intended as a placeholder and does not predict well. NCHRP 9-30A Permanent Deformation of HMA Surface The objective of NCHRP Project 9-30A was to recommend revisions to the HMA rut depth transfer function in the MEPDG software developed under NCHRP Project 1-37A. The recom- mended revisions were based on the calibration and validation of multiple rut depth transfer functions with measured material properties and performance data from roadways and other full-scale pavement sections that incorporate modified or other specialty mixtures, as well as unmodified asphalt binders. The NCHRP 9-30A rutting models for HMA/PCC composite pavements were evaluated and recommendations made for additional research. In summary, all
6three transfer functions did a fair job of predicting the measured rutting values using mixture properties and other pavement layer properties extracted from project files. Thus, the three rut depth transfer functions described and included in NCHRP 9-30A are believed to be reasonable for composite pavements. Lattice Model for PCC/PCC Bonding Extensive work was performed to more fully develop and use lattice models for composite slab simulations for debonding of the top PCC layer from the bottom PCC layer. Completed models coupled the lattice models with finite element models to provide a comprehensive model of the PCC/PCC interface bonding. For model simulations of realistic paving conditions in which newly constructed PCC/PCC pavements are placed in a reasonable time frame, debonding of the layers did not occur. Furthermore, additional simulations of layer behavior took into account unrealistic extreme thermal gradients and highly reduced shear strengths at the interface, and these simula- tions found failure at the interface in only the most extreme of cases, which would not be encoun- tered in the field. This conclusion is supported by observations from the European PCC/PCC experience, as consultants to the R21 project were unable to cite an instance of PCC/PCC debond- ing. Based on these observations and model simulations, it was the assessment of the research team that debonding is only a concern in PCC overlays of existing PCC pavements, which was out of the scope of the SHRP 2 R21 project. Recommendations for Composite Pavement Design Based in part on these models and improvements made to the MEPDG/DARWin-ME software, the following can now be used in the design of new composite pavements: ⢠New HMA/JPC, HMA/RCC or LCB, and HMA/CRC can be designed using the overlay design feature in DARWin-ME. ⢠PCC/JPC and PCC/CRC can be designed using MEPDG (v. 1.3000:R21), which includes modifications to the allowable PCC layer thicknesses, representative PCC layer properties, slab and base interaction properties (full versus zero friction), PCC/PCC subgrade response mod- eling, and the distribution of the temperature nodes representing a thermal gradient through the composite pavement system. Research Products The products from this research can be classified into five broad categories: (1) design, (2) con- struction and materials, (3) training, (4) informational, and (5) other. Design Products MEPDG (v. 1.3000:R21) developed under this study includes modifications to the allowable PCC layer thicknesses, representative PCC layer properties, slab and base interaction properties (full versus zero friction), PCC/PCC subgrade response modeling, and the distribution of temper- ature nodes through the composite pavement system. Many of these revisions specifically targeted the Enhanced Integrated Climatic Model (EICM) used by the MEPDG. This new program will be submitted to the American Association of State Highway and Transportation Officials (AASHTO) for consideration to incorporate the improvements into the DARWin-ME software. In addition, bug fixes and improvements related to both types of composite pavements were made to the MEPDG software throughout the R21 contract (e.g., crack opening error in HMA/CRC), and all of these modifications have been already incorporated into the DARWin-ME software. The structural fatigue damage and cracking models for both types of composite pavement were validated using all available data: MnROAD test sections, UCPRC test sections, and the
7 existing 64 sections located in the United States, Canada, the Netherlands, Germany, and Austria. The existing global calibration factors were determined to be adequate. However, this does not mean that slab thickness will be the same for conventional or two-layer composite pavements. ⢠Various other structural and performance models for key distresses (rutting, joint faulting, smoothness) in new composite pavements were validated. ⢠Several detailed MEPDG design examples for composite pavements were prepared for guid- ance purposes. Comparisons of several examples with conventional JPCP or CRCP indicated a 1- to 3-in. reduction in required thickness for composite pavement. This reduction for HMA/JPC or HMA/CRC was attributable to a reduction in temperature gradients. ⢠Detailed recommended revisions were made to incorporate composite pavements into the MEPDG/DARWin-ME Manual of Practice (MOP). ⢠LCCA guidelines and examples were prepared. The life-cycle costs for composite pavement can be lower than those for conventional HMA or PCC pavements: 4 Use of the MEPDG (v. 1.3000:R21) and DARWin-ME to design HMA/JPC (including jointed RCC or LCB) or HMA/CRC. The HMA surface insulates the PCC slab from both temperature and moisture gradients. This has major implications regarding the reduction of stresses at the top and bottom of the slab and the resulting reduced fatigue damage, especially at the top of the slab. Comparative designs show a significant reduction in composite slab thickness. 4 In urban areas with high congestion and high costs of lane closures, rapid renewal is paramount. HMA/PCC can be designed for the PCC to structurally last to have a long life (if durable materials are used). The thin HMA can be milled and replaced rapidly with minimal disruption to traffic. PCC/PCC has much longer surface life, but when needed, the surface can be diamond ground to rapidly restore smoothness and friction and reduce pavement/tire noise. 4 Where high-quality aggregates for PCC are not available (or expensive because of long haul distances), local PCC aggregates may be susceptible to polishing and other durability-related distresses. In these situations, HMA or PCC surfaces can protect the structural integrity of the PCC and can be milled and diamond ground and rapidly renewed as needed. 4 Many urban areas and some rural areas exist with old PCC pavements that can be removed and processed and recycled directly back into lower layer PCC. This provides excellent improved sustainability opportunities for composite pavements. 4 Where low pavement noise is required, such as in urban areas with large populations in close proximity to the pavements, porous HMA surfacing of PCC provided the lowest level of noise measured. An alternative was discovered at the MnROAD site, where the next generation diamond grinding was performed on the EAC surfacing, and measurements showed the lowest noise concrete surface measured. These surfaces can be renewed rapidly into the future as needed. 4 Arizona has built many miles of major freeways with porous rubberized asphalt surface over new JPC and CRC to minimize noise. Arizona has had success with this type of pavement, but performance data on this type of pavement in other parts of the country are limited. Low noise is a major reason porous HMA/PCC and EAC PCC/PCC composite pavements are constructed in European countries. 4 Where conventional HMA pavements exhibit transverse cracks and deterioration of transverse cracks is a problem, HMA/CRC is a good alternative to eliminate reflection of transverse cracks. No low-temperature transverse cracks were observed in HMA/JPC or HMA/CRC, and no longitudinal wheelpath cracks have been observed in HMA/PCC pavements, either. 4 Composite pavements can be an economical choice when widening existing PCC or HMA/PCC pavement such that the widened section is compatible structurally with the existing pavement. Both the new and the existing lanes typically are covered with one or more lifts of HMA.
8Construction and Materials Products Construction specifications and guidelines were developed as part of construction at MnROAD and UCPRC for use by agencies considering constructing new HMA/PCC and PCC/PCC composite pavements. These include two-lift wet-on-wet construction of PCC/PCC pavements, timing and sequencing of operations, texturing procedures and related guidelines, guidelines for paving the stiffer lower lift PCC and the thin upper lift, saw cutting of joints, and the challeng- ing exposed aggregate brushing technique. The MnROAD construction also involved the use of ultrasonic tomography to assess PCC/PCC layer thicknesses and bond quality at the PCC/PCC and slab/base interfaces. The PCC upper layer was diamond ground using a next-generation grind that produces a smoother and quieter surface. Material specifications include those for recycled aggregate, cementitious materials such as cement and fly ash, aggregate type and gradation for EAC, and retarding/curing compound. Procedural specifications include those related to wet-on-wet construction, timing of paving operations, texturing, saw cutting, sealing of sawed and sealed joints, tack coat application for HMA/PCC. Concrete freezeâthaw durability is a major concern for pavements in many parts of the United States and Canada. The upper layer PCC mixture will experience the most freezeâthaw cycles, but the lower layer mixtures will experience freezeâthaw cycles as well. The International Union of Testing and Research Laboratories for Materials and Structures (Paris) (RILEM) CIF concrete freezeâthaw standard was adopted based on European PCC/PCC experience, and the equipment was imported from Germany for use in the SHRP 2 R21 project. The CIF test evaluates the capil- lary suction, surface scaling resistance, and internal damage of concrete samples exposed to a 3% by volume sodium chloride solution and freezeâthaw cycles, whereas AASHTO T161 evaluates the internal freezeâthaw damage of concrete submerged in water and AASHTO T277 evaluates the freezeâthaw scaling resistance of concrete exposed to a 3% sodium chloride solution. RILEM CIF freezeâthaw testing and evaluations were conducted on all the concrete mixtures used at MnROAD. All of these concrete mixes adequately resisted surface scaling and internal damage (modulus) caused by frost action. Compared with the decrease in relative modulus of other concrete samples studied with the RILEM CIF procedure, the loss of scaled material and the decrease in relative moduli of all of the samples were relatively small. The lack of scaling and internal damage in both lower PCC mixes after 56 freezeâthaw cycles indicated that these mixtures are suitable for use in long-life concrete pavements, despite containing recycled concrete aggregates or having a 60% cement replacement with fly ash, respectively. It was expected that the upper lift PCC samples would experience minimal scaling and internal damage caused by frost action because of: the high cement content and low water-to-cement ratio of the mix, as well as the use of high-quality granite aggregates. Training Products Materials were prepared to promote the use and accelerate the adoption of new composite pavements. The training materials include both design and construction materials. Design examples for both major types of composite pavements are included. Informational Products Includes the R21 final reports (Volumes 1 and 2) and detailed appendices and a database of test sections. Readers may also refer to the previously published report on the European Survey of Composite Pavements by Tompkins, Khazanovich, and Darter in 2010. The database contains material properties, performance, traffic, structure, and location, which are all inputs required for use with the MEPDG/DARWin-ME.
9 Other Products Three test sections (two PCC/PCC and one HMA/PCC) were constructed at MnROAD with various surface textures (exposed aggregate, conventional grind, next-generation grind, HMA) and design features (doweled/nondoweled and with/without sawed and sealed joints for HMA/PCC) with two different PCC mixes in the lower lift. These are the only instrumented in-service composite pavement test sections in existence. The instrumentation includes static and dynamic gauges, moisture gauges, and temperature gauges, all of which are wired into a data acquisition unit for continuously collecting data. These sections were constructed in April through June 2010 and were opened to traffic in July 2010. Instrumented UCPRC HVS test sections were constructed in May 2010 and loaded with the HVS equipment. The instrumented test cells can be used for future testing. Data were collected from rutting and reflection cracking tests at UCPRC (including laboratory testing). HMA/JPC full-scale fatigue cracking tests using the HVS were conducted to validate the MEPDG transverse cracking models, and the results provided validation. Additional testing may continue with other funding sources. Overall SHRP 2 R21 Products Use All of these products are available for use by federal, state, local, and other agencies for design, con- struction, materials, and management of new HMA/PCC and PCC/PCC composite pavements. Examples of Composite Pavements In-service composite pavements have been shown in to provide long lives with excellent surface characteristics, long-life structural capacity, and rapid renewal when needed. Composite pave- ments seem to reflect the current direction of many highway agencies to build more economical yet sustainable pavement structures that use recycled materials and locally available materials. The availability of DARWin-ME and the validation accomplished under R21 have made it possible to design these composite pavements with confidence. Table ES.1 provides examples Table ES.1. Examples of HMA/PCC Composite Pavements in First Performance Period Composite Pavement; Age and No. of Trucks HMA Layer PCC Layer Performance and Maintenance Design, Sustainability, and LCCA ARFC/JPC I-10, Arizona; 17 years and 20 million trucks 1-in. ARFC 14-in. JPC 15-ft joints Dowels Excellent performance; transverse joint reflection low severity; smooth; ARFC has lasted 20 years; no PCC cracks or repairs DARWin-ME requires thinner slab design; low life-cycle cost over many years; no lane closures SMA/JPC A93, Germany; 13 years and 47 million trucks 1.2-in. SMA with saw and seal joints 10.3-in. JPC 16-ft joints Dowels Good performance; transverse joint saw and seal; smooth; no PCC cracks; SMA spall repair DARWin-ME gives same slab design; low life-cycle cost; few lane closures HMA/CRC I-10, San Antonio, Texas; 25 years and 24 million trucks 4-in. HMA 12-in. CRC HMA base Excellent performance; no reflection cracks; smooth; no punchouts; no maintenance DARWin-ME gives thinner slab design; low life-cycle cost over many years; no lane closures HMA/RCC White Road, Columbus, Ohio; 7 years and 70,000 trucks 3-in. HMA with sealed cracks after cracking 8-in. RCC 45-ft joints No dowels Excellent performance; reflection cracks sealed just after cracked; smooth; no maintenance DARWin-ME gives thinner slab design; short joint space; low life-cycle cost; no lane closures HMA/JPC I-94, Minne- sota; 1 year and 600,000 trucks 3-in. HMA with sawed and sealed joints 6-in. JPC 15-ft joints Dowels Excellent performance; sawed and sealed transverse joints good condition; no PCC cracks, smooth; no maintenance DARWin-ME gives same design; PCC contains 50% RCA and 60% fly ash Note: Trucks given for heaviest lane, one direction only.
10 of HMA/JPC and HMA/CRC composite pavements for a wide range of heavy truck traffic in their first performance period. The following is a brief summary of the field performance of HMA/PCC type of composite pavements: ⢠Relatively thin asphaltic surfaces that have performed well include a wide variety of types and thicknesses under heavy traffic: 1- to 2-in. SMA directly on PCC or on HMA on PCC, 2- to 4-in. dense graded HMA over PCC, 1-in. porous HMA over dense HMA/PCC, 1-in. ARFC over PCC projects, and 0.625-in. Novachip over HMA/PCC. There are several successful thin asphaltic surface courses that perform very well over 10 to 15 years. They do not rut significantly. Transverse joint reflection cracks occurred on all JPC and RCC pavements, with most of low to medium severity. Projects in Spain showed that shorter joint spacings (e.g., 10 ft) result in much less reflection cracking and severity. Dowel bars greatly reduced severity of joint reflection cracks on comparative sections in Minnesota. Sawed and sealed joint projects were all in excellent condition and are highly recommended for thin asphaltic surfaces over jointed PCC. ⢠The JPC, RCC, and LCB concrete layers had a wide range of thicknesses from 5 to 14.5-in. with the thicker sections being very overdesigned. The RCC ranged from 6 to 15 in. thick (way overdesigned). The LCB/CTB ranged from 6 to 11-in. None of the JPC, RCC, LCB/CTB, or CRC showed any transverse fatigue cracking, except the 5-in. JPC in Minnesota under heavy traffic. ⢠The CRC layers show a wide range of thicknesses, from 8 to 13 in., with percent reinforcement ranging from 0.55% to 0.70%. The only section with punchouts was a section in Arizona with low steel of 0.55% and 0.5-in. ARFC under very heavy traffic over 16 years. ⢠Joint spacing for JPC typically ranged from 15 to 30 ft. Joints usually were cut in RCC at 15- to 45-ft intervals. Based on other experimental sections in Spain, the shorter joint spacings (e.g., 10 ft) were greatly beneficial in reducing the severity and amount of transverse reflection/shrinkage cracking through the HMA. Sawing and sealing of joints was also greatly beneficial in controlling the severity of the cracks in thin asphaltic surfaces. ⢠Dowels were used on many heavily trafficked JPC sections but many other sections had none. No dowels were used with RCC or LCB/CTB. Reflection cracks dramatically showed the benefits of dowel bars in controlling joint load efficiency and thus a reduction in HMA deterioration over the joints. ⢠Truck traffic ranged from low to very heavy. Typically the following ranges existed in the heaviest travel lane: 4 Interstates and freeways: 1.4 million trucks/year (range: 0.5 to 3.6); 4 Highways: 0.2 million trucks/year (range: 0.1 to 0.3); and 4 Local streets: 0.05 million trucks/year (range: 0.004 to 0.08). ⢠Total trucks in the design lane ranged to 47 million and the age ranged to 45 years. ⢠One section had a total life of 45 years, during which the asphaltic surface was replaced three times but the PCC did not require any repair. This and another similar HMA/JPC are expected to carry traffic continually into the future with no fatigue cracking, thus no slab replacements, and more rapid renewal. In fact, fatigue cracks developed only on the exceptionally thin PCC layers on some experimental sections. None of the typical thickness JPC developed any slab fatigue cracking. Table ES.2 shows examples of HMA/JPC sections that have been through two and three HMA surface replacement cycles that were done rapidly because none of the underlying JPC slabs were cracked and needed replacement. These and other HMA/PCC composite pavements have performed well over many years with only the rapid replacement of the HMA type surface course required. They have performed as âlong-lifeâ pavements. Table ES.3 provides examples of PCC/JPC composite pavements for freeways with heavy truck traffic. These and other PCC/JPC composite pavements have performed well over many years with only the eventual renewal of the surface course required through diamond grinding.
11 Table ES.2. Examples of âLong-Lifeâ HMA/PCC Composite Pavements Over Several Performance Periods Composite Pavement; Age and No. of Trucks Surface and Rehabilitation Base Slab Characteristics Performance and Maintenance Design, Sustainability, and LCCA HMA/JPC I-5, Seattle, Washington; 45 years and 35 million trucks 4-in. HMA original; 2-in. at 13 years; 2-in. at 16 years; 2-in. at 11 years; (some milling at times of resurfacing) 6-in. PCC No joints No dowels Excellent performance; trans- verse cracks at 70 ft reflected medium severity after 8 years; smooth; replaced HMA at 11- to 16-year intervals; no additional transverse cracks; no PCC repairs DARWin-ME would design thicker slab, add doweled transverse joints at 10 to 15 ft; saw and seal would extend life; low life-cycle cost over many years; few lane closures for rehabilitation HMA/JPC I-294, Chicago, Illinois; 19 years and 30 million trucks 1992: 3.5-in. HMA origi- nal; 2001: Milled off and added 3-in. HMA; no additional rehabili- tation after 10 more years 12.5-in. JPC; 20-ft joint spacing Dowels Excellent performance; trans- verse joints reflected medium severity; smooth; replace HMA at 9- to 10-year inter- vals; no transverse fatigue cracks in JPC; no PCC repairs DARWin-ME gives thinner slab design; shorter joint spac- ing; saw and seal joints would extend life; low life- cycle cost over many years Note: Trucks given for heaviest lane, one direction only. Table ES.3. Examples of PCC/PCC Composite Pavement Characteristics, Applications, and Performance Composite Pavement; Age and No. of Trucks Upper PCC Layer Lower PCC Layer Performance and Maintenance Design, Sustainability, and LCCA PCC/JPC I-75, Detroit, Michigan; 18 years and 72 million trucks 2.5-in. EAC 7.5-in. JPC 6-in. LCB 15-ft joint space Dowels Fair performance; no transverse fatigue cracking; no joint fault- ing; smooth; only distress is joint spalling or debonding Designed for very heavy traffic; low expected life-cycle cost; few lane closures PCC/JPC FL-45, Florida; 30 years and 5 million trucks 3-in. PCC 9-in. JPC Lower PCC strength A, B, and C; 15- and 20-ft joint spacing Doweled and nondoweled Excellent performance; low trans- verse fatigue cracking; low joint faulting Pavement somewhat overdesigned; low life-cycle cost; no lane closures over 30 years; savings of cement; good sustainability PCC/JPC A93, Germany; 13 years and 53 million trucks 2.8-in. EAC 7.5-in. JPC 16.4-ft joint space Dowels Tied PCC shoulders Excellent performance; no trans- verse fatigue cracking; no joint faulting; smooth; low noise; pavement should last many more years Designed for very heavy traffic; low life-cycle cost; no lane closures good sustainability PCC/JPC A1, Austria; 14 years and 47 mil- lion trucks 2-in. EAC 7.9-in. JPC (RCA materials) 18-ft joint space Dowels ATB Excellent performance; no trans- verse fatigue cracking; no joint faulting; smooth; low noise pavement should last many more years Designed for very heavy traffic; low life-cycle cost; no lane closures; good sustainability PCC/JPC K-96, Kansas; 14 years and 2.1 mil- lion trucks 3-in. PCC 7-in. JPC 15-ft joint space Dowels PCC shoulders Excellent performance (new pavement); no distress; smooth Pavement overdesigned; low expected life-cycle cost; no lane closures PCC/JPC N279, the Netherlands; 8 years and 11.9 million trucks 3.5-in. EAC 7-in. JPC 15-ft joint spacing Dowels Excellent performance; no trans- verse fatigue cracks; smooth; low noise; no other distress Well-designed; low expected life-cycle cost; no lane closures PCC/JPC I-70, Kansas; 4 years and 3 million trucks 1.5-in. PCC 8 different surface textures 11.8-in. PCC 15-ft joint space Dowels PCC shoulders Excellent performance (new pave- ment); no distress; smooth; low noise; long life expected Designed for very heavy traffic; low life-cycle cost expected PCC/JPC I-94, Minnesota; 1 year and 600,000 trucks 3-in. EAC and diamond grinding 6-in. JPC 15-ft joint spacing Dowels Excellent performance; no trans- verse fatigue cracks; smooth; no maintenance DARWin-ME gave this design for 15-year life, PCC 50% RCA, 60% fly ash, good sustainability Note: Trucks given for heaviest lane, one direction only.
12 A brief summary of the field performance of PCC/PCC type of composite pavements is as follows: ⢠Relatively thin high-quality concrete surfaces include a variety of types and thicknesses: 4 2- to 3-in. PCC over JPC performed well for more than 18 years under very heavy traffic. No debonding of PCC from lower layer PCC was observed, with the exception of some cracking at the transverse joints of the I-75 Michigan project after 18 years. 4 3-in. higher strength PCC over JPC performed well for more than 30 years in Florida. No debonding of the PCC has occurred. ⢠The JPC concrete lower layers had a range of thicknesses from 6 to 9 in. None of the JPC showed any transverse fatigue cracking. 4 Joint spacing for JPC ranged from 15 to 20 ft. 4 Dowels were used on all of these sections because most were heavily trafficked. As a result, joint faulting was not significant. ⢠Truck traffic ranged from medium to very heavy. Typically the following ranges existed in units of trucks per year in the heaviest travel lane: 4 Interstates and freeways: 3.3 million trucks/year (range: 1.8 to 4); and 4 Highways: 0.3 million trucks/year (range: 0.1 to 0.7). Practically none of the PCC/JPC slabs showed any transverse fatigue cracks. ⢠Total trucks in the design lane ranged to 72 million, and the age ranged to 30 years. Implementation Road Map The road to implementation includes continued monitoring of constructed composite test sections at MnROAD. Additional analysis of the instrumentation data and the performance data will be extremely useful for convincing highway agencies of the validity of the concepts, the design procedures, and the construction guidelines and specifications. The MnROAD test sections can be used to hold national and regional open houses or workshops to disseminate information regarding both types of composite pavements. The products developed as part of the SHRP 2 R21 project will result in improved design and life-cycle cost procedures for composite pavements. The guidelines, techniques, and specifica- tions developed in R21 will greatly advance the state of the practice of constructing composite pavements. Composite pavements are congruent with the SHRP 2 Renewal philosophy because they are designed to be long-lasting pavements that can be renewed rapidly. For highway engineers, designers, and agency decision makers, composite pavements provide a cost-effective alternative to conventional concrete and asphalt pavements over the life cycle of the pavement. Together, the R21 reports, software, and guidelines provide information for these technologies to become widely adopted by the transportation community. Based on the comprehensive results achieved from this study, the key characteristics of composite pavements were determined to be: ⢠There are excellent surface characteristics from the thin, high-quality asphaltic or concrete top layers. These include low noise (especially for permeable mixtures), high friction, very good initial smoothness, minimal rutting, and reasonable durability over a 10- to 15-year period. ⢠There is an ability to rapidly renew a thin surface course as it wears under traffic and weather (removal and replacement of asphaltic materials, diamond grinding, or retexturing of concrete materials). ⢠There is long life structural design of the lower PCC layer (designed for minimal fatigue damage over a 40-year period or more). ⢠There is avoidance of certain distress types that occur regularly in conventional pavements but are rare or nonexistent in composite pavements. For example, HMA/JPC or HMA/CRC rarely show top-down HMA or PCC longitudinal cracking in the wheelpaths (thermal gradients are
13 reduced that lowers top-down fatigue damage in PCC); these composites rarely show any low temperature transverse cracking (they are bonded to the PCC); and they show only minimal amounts of rutting. Transverse reflection from JPC joints can be controlled by the saw and seal procedure. Transverse reflection of CRC cracks rarely occurred in the HMA/CRC included in the database. PCC/JPC composite pavement has shown no longitudinal top-down cracking and only small amounts of fatigue transverse cracking. The durability of this surface has led to very little polishing in the wheelpaths. ⢠There are improved life-cycle costs attributable to both lower construction costs and lower maintenance and rehabilitation costs over time. ⢠There are improved sustainability practices through structural and materials design of the lower PCC layer in both types of pavements. Increased use of recycled or alternative materials (RCA, RAP), increased use of more local and less expensive aggregates, and higher substi- tution rates for cementitious materials (higher contents of fly ash or other supplementary cementitious materials).
