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

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14 This R21 project, “Composite Pavement Systems,” fits under the Renewal area, the goal of which is to develop a consistent, systematic approach for performing highway renewal that is rapid, causes minimal disruption, and produces long-lived facilities. The Renewal scope applies to all classes of roads. Two strategies that have shown great promise for providing strong, durable, safe, smooth, and quiet pavements needing minimal maintenance are: (1) surfacing a new portland cement concrete (PCC) layer with a high-quality hot mix asphalt (HMA) layers, and (2) placing a relatively thin, high-quality PCC surface atop a thicker PCC layer. However, the structural and functional performances of these two types of composite pavements were not well understood or documented. Mod- els for predicting the performance of these pavement systems needed to be developed and/or confirmed for use in design, pavement management, and life-cycle cost analysis (LCCA). In addition, guidance on the development of specifications, construction techniques, and quality management proce- dures was needed for these technologies to become widely adopted. Research Objectives and Overview The objectives of this research were to investigate the design and construction of new composite pavement systems, and specifically not those resulting from the rehabilitation of existing pavements. The goal was to 1. Determine the behavior of new composite pavement systems and identify critical material and performance parameters. 2. Develop and validate mechanistic-empirical (M-E) based performance prediction models and design procedures that are consistent with the Mechanistic-Empirical Pavement Design Guide (MEPDG). 3. Develop recommendations for construction specifica- tions, techniques, and quality management procedures for adoption by the transportation community. This project consisted of the following three phases: • Phase 1 consisted of a literature search, survey of various national and international highway agencies, field survey of composite pavements in three European countries, an evaluation of existing design procedures, development of database for full-scale applications, populating the database with information from available projects, and an initial evaluation of existing data. Phase 1 was completed and the Phase 1 interim report prepared and submitted to SHRP 2 in May 2008. • Phase 2 consisted of further completion of the databases, analyzing the databases, identifying failure mechanisms and other distresses relevant to new composite pavements, per- formance modeling, and conducting parametric evaluations of the performance models. Phase 2 also included the devel- opment of the detailed research plan for Phase 3. Phase 2 was completed and the Phase 2 interim report prepared and submitted to SHRP 2 in May 2009. • Phase 3 consisted of implementing the research plan devel- oped in Phase 2. Full-scale roadway sections were constructed and tested at MnROAD. Field composite pavement sites with long-term performance were surveyed, and detailed information was collected in the United States, Canada, and three European countries. The results of these investigations were used to refine and validate the performance models and develop the final design guidelines and procedures. Phase 3 also included the development of construction specifications, design guidelines, and a plan for long-term evaluation and validation of the design models, develop- ment of training materials, and delivery of the final report for this research. C h a p t e R 1 Introduction and Background

15 Overview of Report The purpose of this report is to present the work performed throughout the course of this project. Included are the exec- utive summary and two volumes. Volume 1 covers HMA/PCC composite pavements, and Volume 2 covers PCC/PCC com- posite pavements. Each volume includes six chapters, with Chapter 1 being this introduction and background. Chapter 2 includes details of test sections, and Chapter 3 covers the vari- ous aspects of the research relevant to analysis and modeling. Design and construction guidelines are included in Chapters 4 and 5, respectively. Chapter 6 includes product summary, conclusions, and recommendations for future research. Definitions PCC/PCC composite pavement systems for the purposes of this research are defined as a relatively thin, high-quality concrete surface placed immediately on top of a plastic con- crete layer (Figure 1.1). The lower concrete layer may include increased amounts of recycled materials, including RCA, RAP, and others; increased use of local and less expensive aggregates; and higher substitution rates for cementitious materials (fly ash or other supplementary cementitious materials [SCMs]) that may be less suitable for use in a surface layer at the higher substitution amounts. Construction is accelerated by placing the concrete surface layer on top of the lower concrete layer before the latter has set to facilitate a total bond (no slippage) between the two layers of concrete; this construction tech- nique is commonly called “wet-on-wet” paving. The PCC can be constructed as jointed plain concrete (JPC) or continuously reinforced concrete (CRC). Both PCC layers provide structural capacity, but the lower PCC layer is the primary load-carrying layer (because of the greater thickness) and is expected to provide a durable and strong base that is economical to con- struct and promotes the ideals of sustainability and energy efficiency. The upper PCC layer is expected to provide excel- lent surface characteristics over a long time period and to be rapidly renewable (through diamond grinding or other texturing methods). history The history of PCC/PCC in the United States dates to the first concrete pavement constructed in the country, located in Bellefontaine, Ohio, in 1891 (Snell and Snell 2002). This experimental pavement section featured a 2-in. surface and 4-in. structural layer with water-to-cement ratio (w/c) of 0.60 and a durable wearing course with w/c of 0.45. From roughly 1950 to the mid-1970s, two-lift paving for concrete pavements was very common in many U.S. states for the construction of jointed reinforced concrete pavements (JRCP), which began to disappear in the 1970s as agencies began to move toward jointed plain concrete pavement (JPCP) designs. Appendix B provides a review of the history and background of PCC/PCC composite pavements. In Europe, two-lift paving in the sense of constructing two layers with different properties for the sake of reducing noise, increasing skid resistance, lowering costs, and so forth, has been much more common than in the United States. Austria in particular has been active in regular two-lift paving for concrete pavements, and the standard concrete pavement in Austria is constructed according to two-lift specification (FHWA 1992; Hall et al. 2007). Two-lift paving has been used for special projects in countries such as Switzerland, Belgium, the Netherlands, France, and Germany with regularity since the 1930s and is becoming more common as the techniques are refined. Germany has also used two-lift paving in airport pavements as a way of reclaiming recycled materials (FHWA 1992). Overall, the desire for quieter, more economical and especially more sustainable roadways is motivating many countries to increase the frequency with which concrete pave- ments are constructed in two unique lifts. Much like their European counterparts, American pave- ment engineers have put a great deal of research, design, and construction effort into developing PCC/PCC. There were a limited number of experimental PCC/PCC projects in Iowa, Florida, and North Dakota during the late 1970s and 1980s. The High Performance Concrete Pavement (HPCP) project (FHWA 2006; Larson 2006; and Wojakowski 1998) in particu- lar was responsible for the development of experimental two- lift sections in the 1990s in Michigan and Kansas. These new two-lift experiments had as their larger research goals a desire to increase the service life of concrete pavements, lower life- cycle costs, use innovative designs and materials, and improve construction practices. Florida Test Sections Thirty-three composite PCC/PCC test sections on SR-45 near Fort Myers, constructed in 1978, were designed with 3-in. standard PCC in the top lift and 9-in. lean concrete in the lower lift. The sections were designed to observe perfor- mance and make comparisons between the different pavement Concrete Surfacing (High Quality Aggregate, Good Durable Surface Texture) Concrete Layer (JPCP, CRCP) (Lower Cost Aggregate) Figure 1.1. Typical cross section for PCC/PCC composite pavements.

16 constituents and design properties. The materials under inves- tigation were three types of lean concrete and two subbases. The lean concrete lower lifts differed in terms of the amount of cement (8.5%, 7.3%, and 5.5% by weight), whereas the subbases were either 6-in. cement-treated subgrade (A-3) or 6-in. shell-stabilized subgrade (A-3). The main sections, con- sisting of PCC surfacing, three levels of PCC lower layers, and two joint spacings, performed very well over a 30-year period (ERES Consultants 1998; Greene et al. 2010). The two-layer composite performed better than the one-layer conventional section. The project conclusions stated that “this experimental project has also demonstrated that a two-layer concrete system consisting of a relatively thin higher quality PCC surface over a lower quality econocrete layer and a granular subbase can be a sustainable and long-lasting pavement design alternative” (Greene et al. 2010). Kansas Test Sections The desire to use more innovative materials, such as recycled aggregates, led to the creation of three two-lift test sections on K-96 in Kansas. The K-96 test sections look at three different factors of interest to the Kansas Department of Transportation (DOT): 1. The use of RAP in the lower lift; 2. The use of a durable igneous rock with high alkali silica reactivity as aggregate in the upper lift, instead of an abun- dant limestone in Kansas that has a tendency to polish and reduce skid resistance; and 3. The use of a lower w/c in the upper lift to investigate if the differential volume changes between the two lifts would lead to debonding. Researchers at the Kansas DOT found that the replacement of 15% of total aggregates with RAP in a concrete mix did not affect the workability of the mix and resulted in a durable lower lift for a PCC/PCC. In addition, the researchers were able to counteract the alkali-silica reactivity of the hard igneous rock in the second two-lift section by the replacement of cement with a locally available pozzolanic product. The innovative use of the materials was a success, as tests for expansion indicated volume changes far below what would have been expected had alkali-silica reactivity (ASR) occurred. Finally, the low w/c ratio section showed no shrinkage cracking or evidence of debonding, despite expectations of being difficult. It should be noted that all sections performed well in the long term, although a large number of transverse cracks were observed on the sections with the igneous rock in the upper lift by Kansas DOT in a 2002 annual report. The K-96 project is one of a growing field of research projects that examines PCC/PCC as a potential cost savings and performance increased opportunity through the use of inno- vative materials (Wojakowski 1998). Michigan Test Section One of the first results of the 1992 U.S. TECH scanning tour of European concrete highways (FHWA 1992) was the later development of the 1993 PCC/PCC new construction on I-75 near Detroit, Michigan. The overall goal of the project was to compare the performance of a standard Michigan DOT concrete pavement with its structural PCC/PCC equivalent of European design. Although the research project had this comparison of design performance as its goal, the project also was a testing ground for two-lift paving techniques that had not been attempted in the United States. The I-75 European PCC/PCC sections were placed without serious problems, but the placement went slowly because of the new techniques required for this composite pavement. In constructing these sections, Michigan DOT and researchers from Michigan State University developed numer- ous recommendations for future two-lift paving. These recom- mendations include observations on appropriate sawing depths when forming joints, dowel bar spacing to save costs, minimal thicknesses of surface lifts, and improved techniques for brush- ing away cement in creating surface texture (Weinfurter et al. 1994; Smiley 1995; Smiley 1996; Buch et al. 2000). Kansas Test Sections, 2008 The most significant two-lift concrete pavement project constructed in the United States was done in 2008 on I-70 near Abilene, Kansas (Fick 2008). The construction of this several-mile-long project is part of an innovative technology demonstration of two-lift concrete paving. Both conventional and innovative textures are included. The conventional textures include longitudinal tining, burlap drag, longitudinal groov- ing, and diamond grinding surfaces. The innovative textures include the “next-generation” diamond grinding, along with EAC texture. agency Survey The research team conducted a survey of U.S. and international highway agencies to assess the state of practice and knowledge regarding composite pavement systems. The goals of this survey included the following: • Assessment of the interest of various highway agencies in designing/building composite pavements within their jurisdiction. • Identification of agency contacts and projects that can be used in the R21 database for development of the perfor- mance models.

17 • Gathering information on individual agencies’ experiences with composite pavements and identifying the appropriate contacts for development of guidelines and construction specifications. A list of key agencies to be contacted was developed. These agencies included all 50 states of the United States, the District of Columbia, the provinces of Ontario and Quebec in Canada, and Austria, Belgium, the Czech Republic, Germany, United Kingdom, the Netherlands, Italy, France, Spain, Sweden, South Africa, and Australia. The initial request consisted of a few questions, and agencies that responded positively were contacted for additional information on specific field sections. Responses were received from 35 of 51 (69%) of the U.S. agen- cies and 7 of 14 (50%) of the international agencies contacted. The results of the survey are summarized in Figures 1.2, 1.3, and 1.4 and detailed in Appendix C. Summary of european practices Many European countries have been constructing PCC/PCC composite pavements for several decades and have substan- tial experience with the design and construction of composite pavements. Members of the SHRP 2 R21 research team con- ducted a trip to some of these European countries to better understand and document their experiences with the con- struction of composite pavements. Tompkins, Khazanovich, and Darter (2010) described case studies visited in the Neth- erlands, Germany, and Austria. Austria has been very active in regular two-layer PCC paving for concrete pavements, and the standard concrete pavement in Austria is constructed according to two-layer PCC specification. Austria also has a great deal of experience with the recycling of concrete pavements. In the late 1980s, Austria undertook the long process of recycling PCC pavements that 33 2 2 6 U.S. - No U.S. - Yes International - No International - Yes Figure 1.2. Pie chart depicting agency response to the question “Has your agency constructed new PCC/PCC composite pavements in the past 20 years?” Figure 1.3. Pie chart depicting agency response to the question “Is the design and construction of new PCC/PCC composite pavements of interest to your agency?” 12 13 6 4 No Yes Maybe No response 0 2 4 6 8 10 12 14 16 Cost Reflection cracking and PCC/PCC Bond Lack of experience with this type of construction Lack of long-term data (e.g. for local calibration and LCCA) Acceptance/Resistance to New Technologies Lack of Specifications and Guidelines Surface durability (studded tire wear) Figure 1.4. Key concerns of agencies regarding construction of PCC/PCC composite pavements in their jurisdictions.

18 were 30 years old or more (some of which already were overlaid with HMA) along the A1 motorway into new PCC/PCC com- posite pavements. This experience has led Austrian researchers to claim that the recycling concept is “an important innovation that is both economically and environmentally advantageous.” Two-layer construction requires a consistent, quality effort. Construction techniques were one of two main areas of empha- sis in Germany and Austria (the other emphasis being the qual- ity of the aggregate in the upper layer). As part of the research trip to Europe, the research team studied construction guide- lines, specifications, and practices for constructing PCC/PCC composite pavements and surveyed pavements constructed more than 15 years ago, as detailed in Tompkins, Khazanovich, and Darter (2010). Two-layer PCC paving has been used in countries such as Austria, Switzerland, Belgium, the Netherlands, France, and Germany with regularity since the 1980s, and some much earlier. PCC/PCC composite pavements are becoming more common as the techniques are refined further. European research related to PCC/PCC composite pavements includes construction techniques and the use of recycled materials in the lower layer. Dutch, German, and Austrian researchers report that com- posite pavements provide similar structural performance as an equivalently thick single layer at the same price in Europe, with the added benefits of higher quality, longer life, and friction and noise reduction because of the high-quality top layer. Furthermore, composite pavements allow for the opti- mization of costs and materials throughout the pavement cross section because: • High-quality materials can be used in lesser quantities in the upper layer, where they will be of the most benefit to the system. • Lower quality (cheaper) materials can be used in greater quantities and in the lower layer, where they will contrib- ute structurally without detracting from the quality and performance of the overall pavement. Although there are obstacles to the adoption of composite paving in the United States, it is clear from the European experience that overcoming these obstacles will result in high- quality, durable, and sustainable composite pavements. Distress Mechanisms Key failures in typical PCC pavements should also be con- sidered for PCC/PCC composite pavements. These failure mechanisms include • Bottom-up fatigue cracking for JPC; • Top-down fatigue cracking for JPC; • Longitudinal fatigue cracking for JPC; • Punchouts for CRC; and • Joint faulting for JPC. These individual failure mechanisms are not expected to be a greater concern in PCC/PCC composite pavements than in conventional PCC pavements. PCC/PCC composite pave- ment may also experience some debonding between the layers. Depending on the materials chosen for the lower PCC layer, durability problems may arise in that layer. Details of these distress mechanisms and how they relate to the design of composite pavements are discussed in Appendix E. Longitudinal Fatigue Cracking Longitudinal cracking can be a concern for PCC pavements provided that a PCC pavement is very thin and nondoweled or a significant shrinkage and built-in curling occurs in that pavement. Given that PCC/PCC pavements are sufficiently thick as a result of their layered structure, it is not anticipated that longitudinal cracking caused by insufficient thickness will be a concern for PCC/PCC. Experts on composite pave- ments in Europe concurred that for a slab consisting of hetero- geneous layers, shrinkage and built-in curl and the resulting threat of longitudinal cracking is no more a threat to PCC/PCC than to a structurally similar, single-layer PCC pavement. In addition, this failure was not observed during field surveys of PCC/PCC pavements or was during the 1992 European tour of PCC/PCC pavements. Bottom-Up and Top-Down Fatigue Cracking Both bottom-up and top-down cracking are important modes of failure in single-layer concrete pavements. The main instigator of these modes of cracking is a combination of traffic loading and the “curled,” deformed slab that results from built-in curling and warping and any combination of either temperature or moisture gradients through the slab. Once the slab is in a deformed convex or concave shape, traffic loading creates a cantilever effect that can result in bottom-up or top-down transverse cracking in the pavement slab. Curling is as prevalent in two-layered slabs as it is in single- layered slabs, and for this reason transverse cracking is an important mode of failure for two-layered composite PCC/ PCC pavements. However, after discussions with experts in Europe and from simulations using Lattice3D, it was evident that the built-in stresses in a given two-layered PCC/PCC slab are not exacerbated simply by the layers being heterogeneous. Provided that a two-layered system is constructed using wet-on-wet methods, the slab’s performance in transverse cracking is not significantly different than that of a structurally equivalent single-layered conventional PCC pavement.

19 Joint Faulting Although joint faulting is a concern for single-layer JPCPs, it is not more of a concern in PCC/PCC composite pavements than in JPCPs. As in the case of the heterogeneous-layered slab response to transverse cracking, the presence of hetero- geneous layers in a slab does not exacerbate faulting relative to that of a structurally equivalent JPCP. Joint faulting is no more or less likely to occur in PCC/PCC than it is in single- layered PCC due to the classical causes of joint faulting: base, subbase, subgrade erodability; subpar load transfer efficiency (LTE); or oversaturation of the base near the joint, and the same models for JPC pavement faulting can be used for PCC/PCC composite pavements. Debonding Debonding is a particularly challenging issue that is aggravated by shrinkage and thermal gradients through the hetero geneous layers at early ages. With proper wet-on-wet construction tech- niques, debonding of the two PCC layers is not expected to be an issue. However, as the time between placing the two PCC lifts increases (greater than 90 minutes), the lower PCC lift starts hydrating, and the surface of the lower lift may no lon- ger be “wet.” In such situations, the bond between the two lifts potentially can be compromised. To account for debonding in PCC/PCC, the SHRP 2 R21 research considered nonuniform shrinkage, nonuniform thermal expansion/contraction (espe- cially at early ages), nonlinear thermal gradients, nonuniform heat of hydration, and crack formation and propagation. Freeze–Thaw Durability and Performance Complications of RCA Use The use of RCA or local materials of lower quality can be expected in the lower layer PCC mix. Therefore, durability is an important consideration in the performance of PCC/ PCC composite pavements. This is especially important given that a key difference between RCA and natural aggregate is the variability in the absorption capacity of different RCAs, attributable in part to the existing mortar surrounding the original aggregate. Construction Defects Construction defects that occur during placement of PCC/ PCC composite pavements are the same type as those found in typical JPCP or CRCP. Construction defects include vibra- tion issues, such as inadequate consolidation of the PCC mixes around dowel bars or reinforcing steel, overmixing of the two PCC lifts, improper dowel bar placement, PCC mix issues (such as slump, gradation, temperature, and so forth), improper texturing or curing, and mechanical issues related to the paver. Construction defects can be reduced only with an adequate quality control/quality assurance (QC/QA) and inspection program. Use of pCC/pCC Composite pavements Key questions often asked with regard to PCC/PCC composite pavements are: Where will composite pavements be used, and what will be the demand? PCC/PCC composite pavements allow the pavement designer to design pavements using the best qualities of two different PCC mixes to produce a more functional and economical structure that generally is cost- effective in terms of service throughout its life. Specifically, PCC/PCC composite pavements are optimal solutions for the following situations: • When PCC/PCC is the less expensive alternative. In some design situations, based on materials, climate, traffic, and support conditions, the life-cycle costs for PCC/PCC com- posite pavements can be lower than those of conventional PCC pavements. This is particularly true when quality local aggregates are not available or aggregates are expensive because they need to be hauled long distances to the project location. In these situations, a high-quality PCC surface can protect the structural integrity or avoid the polish potential of the lower PCC layer made for lower quality materials. • Where low maintenance pavement is desired. In urban areas with high costs of lane closures, rapid renewal is paramount. PCC/PCC pavements can be designed for the pavement to have a long life, structurally speaking (if durable materials are used in both layers). The high-quality PCC surface can be retextured rapidly through diamond grinding (or other methods) with minimal disruption to traffic over time. The retextured surface can also be expected to have high durabil- ity because of the hard aggregate and PCC mix quality and strength. • When recycling is an option. 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 for use in PCC/PCC composite pavements. This provides excellent improved sustainability opportunities for pavements. • When low pavement noise is needed, such as in urban areas with large populations in close proximity to the pavement. The high quality of the surface PCC layer makes any sur- face texture durable. As such, low-noise textures, such as those achieved with conventional diamond grinding, next- generation diamond grinding, EAC, and others, can be expected to last longer and, when needed, can be redone with another durable surface texture. • Where avoidance of certain distress types related to the PCC surface is needed. A higher-strength PCC surface layer with high-quality aggregates may be beneficial in

20 reducing or eliminating top-down cracking, surface wear down (wheelpath rutting from studded tires), and polishing of the surface. Differences between Conventional JPCP or CRCP and PCC/PCC Composite Pavement There are several key differences that should provide for superior performance of a new PCC/PCC composite pavement compared with that of conventional JPCP or CRCP. • 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 durability over a long time period (beyond 20 years) even under harsh weather conditions. • Long-life structural design of the lower PCC layer (e.g., designed for minimal fatigue damage over a period of 40 years or more, which may require a thicker layer), where lower cost materials can be used. • Higher-strength PCC surface layer may be beneficial to reduce or eliminate top-down cracking (depending on thick- ness, strength, climate, traffic, and other factors), CRCP punchouts, and surface wear down (wheelpath rutting from studded tires).