Composite Pavement Systems, Volume 2: PCC/PCC Composite Pavements (2013)

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103 Conclusions The SHRP 2 R21 project on composite pavement systems conducted extensive in-depth research on two types of com- posite pavements: 1. High-quality, relatively thin, hot-mix asphalt (HMA) surfac- ing over a new portland cement concrete (PCC) structural layer (e.g., JPC, CRC, jointed RCC, or LCB/CTB). 2. High-quality, relatively thin PCC surfacing atop a thicker structural PCC layer (e.g., JPC, CRC). Composite pavements have been proven in Europe and in the United States to provide long lives with excellent surface characteristics (low noise, smoothness, and high friction), structural capacity, and rapid renewal when needed, and they use recycled and lower-cost materials in the lower PCC layer. Composite pavements also reflect the current direction of many highway agencies to build economical sustainable pavement structures that use recycled materials and make use of locally available materials. Both types of composite pavements have strong technical, economical, and sustainability merits in fulfilling the key goals of the SHRP 2 program, including long-lived pavements, rapid renewal, and sustainable pavements. The objectives of this research were to investigate the design and construction of new composite pavement systems for all levels of highways and streets. This chapter provides a summary of research conclu- sions for PCC surfaces over a PCC lower layer. PCC for the thin surface course is used generically to cover surfaces with various surface textures, including: 1. High-quality concrete with exposed aggregate concrete (EAC) texture. 2. High-quality concrete with very durable nonpolishing aggregate that can be diamond ground. 3. High-quality concrete that is conventionally textured. 4. Normal quality concrete that is diamond ground or con- ventionally textured. The lower PCC layer includes JPC or CRC but may include recycled or alternative materials (RCA, RAP), increased use of more local and less expensive aggregates (e.g., aggregates susceptible to polishing), and higher substitution rates for cementitious materials (higher fly ash or other SCM contents). As part of this research, the R21 research team 1. Determined the behavior, material properties, and per- formance for PCC/PCC composite pavement under many climate and traffic conditions. Experimental composite pavements were constructed at the MnROAD research site and were instrumented and monitored under climate and heavy traffic loadings. Extensive field surveys were performed in the United States, Canada, and Europe of 15 sections of PCC/PCC composite pavements. The bottom line on these performance studies is that PCC/PCC com- posite pavements have clear advantages over conventional PCC pavements in terms of cost, sustainability, and long structural lives coupled with rapid renewal of the surface. 2. Evaluated, improved, and further validated the various structural, climatic, material, performance prediction models, and design algorithms that are included in the AASHTO MEPDG, and the Lattice 3D PCC/PCC bonding model. A special version of R21 MEPDG Overlay design procedure for bonded PCC over JPCP or CRCP (MEPDG version 1.3000:R21) can be used for “New” PCC/PCC composite pavements. A summary of the key analysis and performance findings were included in Chapter 3. 3. Detailed recommendations provided for inputs and modi- fications to the DARWin-ME software for composite pave- ments. Recommended revisions for the AASHTO MOP are also provided. 4. Developed practical recommendations for construction specifications and techniques, life-cycle costing, and training materials for adoption by the transportation community. The products developed as part of SHRP 2 R21 will result in improved design and life-cycle cost procedures for C h a p t e r 6 PCC/PCC Conclusions and Recommendations for Future Research

104 composite pavements. The guidelines, techniques, and speci- fications developed in SHRP 2 R21 will greatly advance the state-of-the-practice of constructing composite pavements. Composite pavements are congruent with SHRP 2 Renewal philosophy because they are designed to be long-lasting pave- ments that can be rapidly renewed. For highway engineers, designers, and decision makers at agencies, composite pave- ments provide another tool in the designers’ arsenal and can be a cost-effective alternative to conventional concrete and asphalt pavements over the life cycle of the pavement. Together these reports, software, and guidelines provide information for adoption by the transportation community and for these tech- nologies to become widely adopted. Based on the comprehensive results achieved from this SHRP 2 R21 study, the key characteristics of PCC/PCC composite pavement was determined as follows: • Excellent surface characteristics from the thin, high-quality concrete surface layer. These include low noise, high friction, very good initial smoothness, minimal wear over time, and high surface durability over a long time period beyond 20 years even under harsh weather conditions. • Ability for rapid renewal of a thin surface course as it wears under traffic and weather (e.g., diamond grinding in various forms or some other type of retexturing). • Long life structural design of the lower PCC layer (e.g., designed for minimal fatigue damage over a 40- to 100-year period). • Avoidance of certain distress types that occur regularly in conventional pavements but are rare or nonexistent in PCC/PCC composite pavements. Table 6.1 shows the direct comparison for conventional PCC and composite PCC/PCC pavement. • Improved life-cycle costs over a long life span because of overall lower construction costs (e.g., increased recycling, local aggregates, cement substitution amounts) and low future maintenance (e.g., high-quality PCC surface will be more durable) and rehabilitation costs over time (e.g., no full-depth repairs of PCC slab because of reduction in fatigue damage). • Improved sustainability practices through structural and materials design of the lower PCC layer: increased use of recycled materials (RCA, RAP), increased use of more local and less expensive aggregates, and higher substitution rates for cementitious materials (higher fly ash contents and other SCMs). Intended audience, Usage, Value added to State of the practice and State of the art, potential Benefits of acceptance and Implementation The key products of the SHRP 2 R21 project on composite pavements include • Examples of the performance of composite pavements; • Design procedures; • Construction guidelines; • Pavement selection type guidelines; and • Training materials. The key intended audiences for these products are as follows: • State highway agency managers, engineers, and consul- tants. New composite pavements need to be added to the Table 6.1. Comparison of Conventional PCC Pavement with Composite PCC/PCC Pavement for Several Key Distress Types Distress Type Conventional JPCP and CRCP Composite PCC/JPC and PCC/CRC Pavement Bottom-up slab fatigue cracking Yes, major design concern. Yes, major design concern. Top-down slab fatigue cracking and top-down fatigue cracking for punchouts Yes, major design concern. Yes, major design concern. If higher strength PCC is used in the top surface, this is less of a concern and this damage mechanism may be reduced. Top-down longitudinal fatigue cracking and corner breaks Yes, this has occurred on some projects. No, this was not observed on any PCC/PCC composite project. Higher strength PCC surface layer may be beneficial here. Surface wear-down (rutting) Yes, this has occurred on projects in studded tire states/areas. Minor on most composite pavements in nearly 20 years in Austria because of high quality aggregates and high cement content. Polishing of surface (poor friction) Yes, this has occurred on many projects resulting from polishing aggregates. Higher quality aggregates are costly if used throughout the entire PCC slab thickness. EAC surfacing in Austria and Germany, where there is extensive snow and ice, has shown only minor polishing in the wheel- paths over 20 years. Use of the highest quality aggregates in the thin top layer would minimize polishing from occurring and lower construction costs. Joint faulting Yes, major design concern. Yes, major design concern.

105 routine pavement type selection procedures of state and local highway agencies. The performance examples, design tools, pavement selection type guidelines, construction guidelines and specifications, and training materials will all provide significant value-added technology to these engineers and managers regarding composite pavements. If DARWin-ME is upgraded to include composite pavements as a new pavement type along with the conventional types, this will be a major advancement in the consideration of composite pavements in the industry. • Federal Highway Administration management and engi- neers. FHWA managers and engineers need to be made more aware of the past performance and benefits of composite pavements so they can discuss the possibil- ity of adding them to their regular pavement selection process. The SHRP 2 R21 products provide the needed information. • Researchers from academia, federal and state agencies, and industry. There are lots of additional opportunities to improve on the design and construction of composite pavements that open up the future of additional research. Making faculty more aware of the advantages of composite pavements and getting this instruction into the classroom is key to educating students about the benefits of composite pavements. The training materials and various documents from the R21 project will be valuable for universities for future course development. The key benefits of state and local highway agencies incor- porating PCC/PCC composite pavements into their routine pavement type selection process include the following: • PCC/PCC composite pavements provide more flexibility in the highway agency pavement management strategy for new and especially for future rehabilitation and are another tool in the designers’ toolbox. The design of composite pavement to achieve lower life-cycle costs, increased sustainability, and longer life will require additional efforts in design, materials, and construction specifications by the highway agency to achieve these goals because new technology is involved. • A PCC/PCC composite pavement can be designed cost- effectively to have a life span similar to that of a conventional PCC pavement. It also can be designed to be a much longer term (long-life) pavement with minimal structural fatigue damage over many years, and the surface will provide long life, but it can be rapidly renewed as needed by retexturing (grinding) with no deep structural problems that require additional lane closures to repair and cure. The long-term LCCA and sustainability should show favorable results for this type of design strategy. • Excellent surface characteristics can be provided. This includes the following: 4 Very smooth surfaces (e.g., initial IRI of 50 in./mi has been achieved for PCC/PCC composite pavements). 4 Low noise surfaces (e.g., EAC, conventional and ultimate diamond grinding). 4 High friction over the long term with high-quality nonpolishing aggregates in the top layer. • Rapid retexturing of the PCC surface through diamond grinding or other technology that may evolve over time. This would reduce traffic congestion over many years. The diamond grinding or other technology would last longer because it has a very hard nonpolishing aggregate in the surface. • Improved sustainability can be provided for composite pavements in several ways: 4 Increased composite pavement longevity is a key to improved sustainability. ▪ The PCC/PCC type of composite pavement can be designed for a very long fatigue damage life, such as 40 to 100 years using the MEPDG (version 1.3000:R21) at a high level of reliability. Slab thicknesses required are comparable to those for single-material JPCP or CRCP. The design can include minimal slab fatigue cracking over the design period. Longevity is a key component of sustainability. ▪ The thin, high-quality PCC surface should also last a long time (e.g., >20 years in harsh climates) based on field projects surveyed in Europe. ▪ The rapid renewal of the surface through some type of diamond grinding will provide excellent surface characteristics, including smoothness, low noise, and good friction over the life of the pavement. ▪ This PCC/PCC composite pavement design will thus reduce the amount of lane closures over the long design life of the pavement. This has a major sustainability impact because of the reduction in emissions caused by the extra congestion due to lane closures for main- tenance and rehabilitation. 4 Reduction of the use of natural resources is another key for improved sustainability. RCA was used successfully in the lower PCC slab in the MnROAD R21 section. The existing concrete from Minnesota I-94 was recycled as 50% of the coarse aggregate. There may be many proj- ects in which such recycling of existing old PCC and old HMA/PCC pavements into the new composite pavement would result in a major reduction of the haul distances involved, which would result in lower energy use and costs. Of course, the use of recycled concrete results in a savings of natural aggregates. 4 Increased use of fly ash in achieving a substantial reduction in portland cement content in the lower

106 4 Increased use of lower-cost local aggregates in the lower PCC layer because the lower PCC is no longer the wearing course that will polish. The higher quality PCC surface provides some protection from freeze–thaw damage and wet–dry cycling. The use of local aggregates improves sustainability by reducing resources spent in hauling aggregates over long distances. recommendations for additional Development or refinement of the products Each of the R21 products is listed in Table 6.2 along with recom- mendations on required future development and refinement that are needed for full implementation. PCC slab. The lower layer of the two I-94 composite sections contained 40% and 60% fly ash replacement, respectively. The use of RCA, 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, reducing carbon dioxide emissions, and minimizing pollution. 4 There exist highways in certain states of the United States where studded tire wear is the major cause of deterio- ration and needed rehabilitation. A high-quality PCC surface, whether it is EAC, ultimate diamond ground, or conventional texturing, would provide a more durable surface that would resist wear of studded tires caused by the high-quality aggregates used in the surface layer. Table 6.2. SHRP 2 R21 Project Recommendations for Additional Development of PCC/PCC Products SHRP 2 R21 Product Implementation Status Additional Development Required Comment MEPDG R21 version software R21 improvements to “Bonded PCC/ PCC” to simulate new PCC/PCC and address limitations of existing structural and environmental models for PCC/PCC. Can be used for design of PCC/JPC, PCC/CRC, HMA/JPC, and HMA/CRC. None. MEPDG (version 1.3000 R21) is avail- able from SHRP 2 and AASHTO. Use “Overlay” design procedures for “New” PCC/PCC composite pavements with appropriate inputs. AASHTO DARWin-ME software “Overlay” design cannot be used to design “New” PCC/PCC composite pavement. Modifications are needed as described. Significant modifications for PCC/PCC that were made in the R21 version need to be made to DARWin-ME soft- ware. User interface requires revision to show PCC/PCC and HMA/PCC composite pavements as “New” pavement alternatives. Improvements should be made as soon as possible for highway agencies to design “New” com- posite pavement. AASHTO MOP Detailed recommendations were prepared to include “New” composite pavements. None. Revision can be made in tandem with modifications to the DARWin-ME software. MnROAD PCC/JPC test section Two PCC/PCC composite sections constructed, instrumented, and being monitored under heavy interstate traffic for one full year. Construction and first year’s performance measured. Monitoring of the section over time would produce valuable longer-term information to convince highway agencies to build composite pavements. These sections should be monitored at least twice a year. Full perfor- mance will not be known for more than 10 years. Many major findings will be discovered over time for structural, texture, and sustainabil- ity. These data can be used to update calibration coefficients and further verify long-term MEPDG structural responses to traffic and thermal loading and refine models (e.g., IRI and reflection cracking as appropriate). 2008 Survey of European Composite Pavements Report completed and available online: www.trb.org/Main/Blurbs/ 163693.aspx. None. Already available to the public. There has been a great deal of interest. (continued on next page)

107 Database of PCC/PCC Composite Pavements Data collected for 15 PCC/PCC composite sections are available in Excel spreadsheet and MEPDG input files. None. These data may be of interest to agencies wishing to develop designs for new composite pavements. Lattice model for PCC/PCC bond The model was further developed and connected to an FEM to analyze PCC/PCC bond conditions. Additional work remains to be done to extend this valuable research software into a practical tool. This program showed that new PCC/PCC composite has sufficient bond if constructed properly. JPCP fatigue cracking models in MEPDG The JPCP model was validated for both HMA/JPC and PCC/JPC composite pavement data. None. The global coefficients are sufficient. JPC fatigue damage in composite pavements is critical to their structural design. Life-cycle cost analysis (LCCA) guidelines Recommendations using the FHWA RealCost spreadsheet for composite pavements were developed. None. The MEPDG predictions can provide pavement life estimation for use in LCCA. Instrument data Extensive instrumentation data exist for MnROAD and included as SHRP 2 R21 database. The full analysis of these data was not possible under R21, and much additional analyses can be accomplished. Some valuable data on temperature, moisture, strains from climatic change, and dynamic strains from loadings. Examples of PCC/PCC composite designs A range of examples of composite pavement design and performance were used in R21. Additional research into addi- tional aspects of composite pavements can be accom- plished with these data. The performance of most composite pavements was very good. These sections can be used to demon- strate this to highway agencies. Construction specifications for PCC/JPC The MnROAD specifications are available and cover a variety of aspects of PCC/PCC construction. None. Key aspects are PCC bonding, PCC lower layer mixture RCA characteristics, SCM replacement, upper layer mixture characteristics, brushing of EAC, curing/retarding of PCC, texturing, and wet-on-wet paving. RILEM CIF concrete freeze–thaw standard Equipment was checked out and many PCC samples tested. Very useful results were obtained. Additional testing on all quality levels of aggregate is recom- mended. This equipment should be more fully evaluated for U.S. applications. An excellent field simulation for freeze–thaw damage of a given PCC. Training products Presentations on design, construction, materials, performance, and exam- ples of both types of composite pavements. None. A variety of presentations are available for use in promoting composite pavements, as is technical training of engineers and contractors. Advantages of composite pavements R21 has brought to light the many advantages of PCC/PCC pavements. Development of design and cost comparisons for conventional design versus composite designs at specific sites. Direct comparison of designs and costs makes a strong convincing case for PCC/PCC composite pavements. Table 6.2. SHRP 2 R21 Project Recommendations for Additional Development of PCC/PCC Products (continued) SHRP 2 R21 Product Implementation Status Additional Development Required Comment