Long-Term Plan for Concrete Pavement Research and Technology— The Concrete Pavement Road Map (Second Generation): Volume II, Tracks

TRACK 2. PERFORMANCE-BASED DESIGN GUIDE FOR NEW AND REHABILITATED CONCRETE PAVEMENTS

Track 2 Overview

Under this track, the concrete pavement research community will attempt to develop a mechanistic approach to pavement restoration and preservation strategies. This track builds off of the comprehensive work done under NCHRP 1-37A that led to the development of the MEPDG and subsequently the AASHTOWare^® DARWin-ME^TM product.⁽¹⁾ The problem statements in this chapter will improve the models, designs, rehabilitation efforts, and all aspects of the work done under NCHRP 1-37A. This track relies on a detailed understanding of the MEPDG, committing researchers to the power of modeling and predictions.⁽¹⁾ However, the CP Road Map also identifies the need for simplified mix design procedures for cities and counties, as well as a design catalog approach. Because many materials properties are important to design success, it is critical that the research conducted under this track is coordinated closely with the work in track 1.

Empirical approaches to concrete pavement design are effective when the conditions remain basically the same, the focus is on structural design, and the attention is not on understanding and managing distress or failure modes. Today, the pavement design practice is primarily empirical, although the state of the practice is moving toward mechanistic approaches. The primary source of much of today’s pavement design is still the American Association of State Highway Officials’ (AASHO) road test of the 1950s. This one subgrade, one base, one climate, and limited traffic design guide was constructed using better-than-normal construction practices. Data analysis techniques were also fairly basic, and the incorporation of reliability was insufficiently understood. Moreover, the AASHO road test did not incorporate many of the concepts and products used today in concrete pavement practices, including concrete overlays, permeable bases, different cements, dowel bar retrofits (DBRs), and other necessary repairs.

Today, the state of the practice is rapidly moving toward mechanistic-empirical (M-E) approaches, particularly with the AASHTOWare^® release of DARWin-ME^TM and the expressed interest of many States.⁽¹⁾ These M-E approaches will allow the designer to account for new design features and characteristics, many materials properties, changing traffic characteristics, and differing construction procedures (such as curing and day/night construction). The designer now can consider additional design features and focus more on pavement performance, including limiting key distress types.

In continuing this work, this track not only looks to the next generation of modeling improvements, but it considers integrating design with materials, construction, presentation, and surface characteristics. This track also explores the development of new high-speed computer analysis tools for optimizing pavement design that can address changes to multiple inputs and thus offer better data on potential life-cycle costs and reliability.

The following sections summarize the goal and objectives for this track and the gaps and challenges for its research program. A table of estimated costs provides the projected cost range for each problem statement depending on the research priorities and scope determined in implementation. The problem statements, grouped into subtracks, follow.

Track 2 Goal

Mechanistic-based concrete pavement designs will be reliable, economical, constructible, and maintainable throughout their design life and meet or exceed the multiple needs of the traveling public, taxpayers, and the owning highway agencies. The advanced technology developed under this track will increase concrete pavement reliability and durability (with fewer early failures and lane closures) and help develop cost-effective pavement design and rehabilitation.

Track 2 Objectives

The track 2 objectives are as follows:

1. Develop viable (i.e., reliable, economical, constructible, and maintainable) concrete pavement options for all classes of streets, low-volume roads, highways, and special applications.
   
   
2. Improve concrete pavement design reliability, enhance design features, reduce life-cycle costs, and reduce lane closures over the design life by maximizing the use of fundamental engineering principles through mechanistic relationships.
   
   
3. Integrate pavement designs with materials, construction, traffic loading, climate, preservation treatments, rehabilitation, and performance requirements to produce reliable, economical, and functional (i.e., noise, spray, aesthetics, friction, texture, and illumination) designs.
   
   
4. Integrate traditional structural pavement design with materials, construction, traffic loading, climate, preservation treatments, rehabilitation, and performance inputs that will produce reliable, economical, and functional (i.e., noise, spray, aesthetics, friction, texture, and illumination) designs.
   
   
5. Design preservation and rehabilitation treatments and strategies using mechanistic-based procedures that use in place materials from the pavement structure to minimize life-cycle costs and construction and maintenance lane closures.
   
   
6. Develop and evaluate new and innovative concrete pavement designs for specific needs
   (e.g., high traffic, residential traffic, and parkways).

Track 2 Research Gaps

The task 2 research gaps are as follows:

• Insufficient understanding of factors that improve design reliability.
  
  
• Pavement designs that lack design reliability for all occasions.
  
  
• Insufficient information to design low-volume local jurisdictions effectively.
  
  
• Lack of design integration with materials, construction, and rehabilitation factors.
  
  
• Lack of methods for conducting multiple high-speed design analyses and sensitivity studies.
  
  
• Lack of fundamental relationships for preservation and rehabilitation designs.
  
  
• Insufficient understanding of pavement foundations and the proper selection of base, subbase, and subdrainage elements.
  
  
• Lack of new and innovative concrete pavement designs.
  
  
• Insufficient understanding of the issues surrounding multiple traffic lane design.

Track 2 Research Challenges

The track 2 research challenges are as follows:

• Consider all significant variabilities and uncertainties properly, develop M-E pavement design reliability methodology that considers all sources of variability directly, and produce concrete pavement designs that meet the desired reliability level (not over- or under-designed).
  
  
• Design pavements reliably and with innovations for unconventional concrete pavement needs such as concrete overlays, low-volume solutions, very heavy traffic, stage construction with low initial costs, and tunnels.
  
  
• Obtain design, materials, traffic, and performance data for low-volume roads to help calibrate and validate the design procedure.
  
  
• Understand fundamental material properties using appropriate test procedures, develop improved pavement response and distress models, and understand and model complicated relationships between structural design, mix designs, and construction factors.
  
  
• Determine the impact of the design changes inherent with MEPDG (DARWin-ME^TM), develop high-speed computer analyses to better implement an incremental damage approach, and encourage users to continue developing mechanistic concepts.⁽¹⁾
  
  
• Reduce reliance on empirical relationships, consider more fully the existing subgrade and pavement design and condition and the options for dealing with it in structural rehabilitation design, and model the impact of preservation treatments and rehabilitation treatments.
  
  
• Understand and capture more fully the 30 years of experience with permeable bases and drains, better understand erodibility and bonding, identify the times when subdrainage and layer permeability are needed and when outlets for the permeable layer (e.g., daylighting) must be improved, and improve environmental stewardship by using recycled materials in the foundation.
  
  
• Establish a clear rationale for new and innovative design sections; overcome the incremental improvement mentality for wholesale rethinking; and build, test, and evaluate innovative sections.
  
  
• Determine the number of lanes and shoulders that can be tied together for given projects and determine tie-bar design for specific project conditions.

Research Track 2 Estimated Costs

Table 8 shows the estimated costs for this research track.

Table 8 . Research track 2 estimated costs.

Problem Statement	Estimated Cost
Subtrack 2-1. Design Guide Structural Models
2-1-1. Development of Benchmark Problems for Concrete Pavement Structural Models Validation	$500,000–$700,000
2-1-2. Improvement of Two-Dimensional and/or Three-Dimensional Structural Models for Jointed Plain Concrete Pavement and Continuously Reinforced Concrete Pavement Used for Reconstruction and Overlays	$5–$6 million
2-1-3. Development of Model for Erosion Related to Material Properties under Dynamic Wheel Loading	$800,000– $1.2 million
2-1-4. Improvements to Dynamic Modeling of Concrete Pavement Systems for Use in Design and Analysis	$800,000– $1.2 million
2-1-5. Structural Models for Special New Types of Concrete Pavements and Overlays	$1–$2 million
Subtrack 2-2. Design Guide Inputs, Performance Models, and Reliability
2-2-1. Enhancement and Validation of Enhanced Integrated Climatic Models for Temperature, Moisture, and Moduli	$1–$2 million
2-2-2. Development and Enhancement of Concrete Materials Models for Improved Pavement Design	$5–$6 million
2-2.3. Enhancement and Validation of Traffic Loading Models Unique to Concrete Pavements	$600,000– $1 million
2-2-4. Improved Jointed Plain Concrete Pavement Deterioration Models	$1.5–$2.5 million
2-2-5. Improved Continuously Reinforced Concrete Pavement Cracking and Punchout Prediction Models	$1.5–$2.5 million
2-2-6. Improved Consideration of Foundation and Subdrainage Models	$1–$1.5 million
2-2-7. Identify and Implement New and Practical Ways to Incorporate Reliability into Concrete Pavement Design and Rehabilitation	$3–$5 million
Subtrack 2-3. Special Design and Rehabilitation Issues
2-3-1. Concrete Pavement Design Aspects Related to Multiple/Additional Lanes	$800,000– $1.5 million
2-3-2. Characterization of Existing Concrete or Hot Mix Asphalt Pavement to Provide an Adequate Rehabilitation Design	$3.5–$4.5 million
2-3-3. Improvements to Concrete Overlay Design Procedures	$4–$4.5 million
2-3-4. Improvements to Concrete Pavement Restoration/Preservation Procedures	$2–$3 million
2-3-5. Development of New and Innovative Concrete Pavement Type Designs	$1–$2 million
2-3-6. Optimizing Procedure for New Design and Future Maintenance and Rehabilitation Capable of Minimizing Total Life-Cycle Costs, Lane Closure Time, and Other Design Goals over the Range of Design Life	$1–$2 million
Subtrack 2-4. Improved Mechanistic Design Procedures
2-4-1. Incremental Improvements to Mechanistic-Empirical Pavement Design Guide Procedures	$1.5–$2.5 million
2-4-2. New MEPDG Procedures for Paradigm Shift Capabilities	$2–$4 million
Subtrack 2-5. Design Guide Implementation
2-5-1. Implementation of the Mechanistic-Empirical Pavement Design Guide	$2–$3 million
Total	$40.5–$59.6 million

Track 2 Organization: Subtracks and Problem Statements

Track 2 problem statements are grouped into the following five subtracks:

• Subtrack 2-1. Design Guide Structural Models.
  
  
• Subtrack 2-2. Design Guide Inputs, Performance Models, and Reliability.
  
  
• Subtrack 2-3. Special Design and Rehabilitation Issues.
  
  
• Subtrack 2-4. Improved Mechanistic Design Procedures.
  
  
• Subtrack 2-5. Design Guide Implementation.

Each subtrack is introduced by a brief summary of the subtrack’s focus and a table listing the titles, estimated costs, products, and benefits of each problem statement in the subtrack. The problem statements follow.

SUBTRACK 2-1. DESIGN GUIDE STRUCTURAL MODELS

This subtrack identifies and frames the next generation of structural models for conventional pavements, as well as the models needed for new and innovative structures. This subtrack is tied closely to the output from the MEPDG.⁽¹⁾ Table 9 provides an overview of this subtrack.

Table 9. Subtrack 2-1 overview.

Problem Statement	Estimated Cost	Products	Benefits
2-1-1. Development of Benchmark Problems for Concrete Pavement Structural Models Validation	$500,000–$700,000	Data that validates current and future structural models for concrete pavements and accurate structural models that improve the performance prediction of concrete pavements.	Accurate structural models that improve the performance prediction of concrete pavements.
2-1-2. Improvement of Two-Dimensional and/or Three-Dimensional Structural Models for Jointed Plain Concrete Pavement and Continuously Reinforced Concrete Pavement Used for Reconstruction and Overlays	$5–$6 million	Improved two-dimensional (2D) and three-dimensional (3D) finite-element model (FEM) that provides significantly improved computation of stresses and deflections for jointed plain concrete pavement (JPCP) and CRCP used in reconstruction and as overlays and pavement performance prediction models that more accurately predict pavement distress and life for incorporation into a new version of the pavement design guide.	Improved characterization of design features, interlayer relationships, and material properties. FEMs incorporated into new versions of the pavement design guide.
2-1-3. Development of Model for Erosion Related to Material Properties under Dynamic Wheel Loading	$800,000–$1.2 million	A comprehensive base/ subgrade erosion test and model capable of predicting vertical and horizontal displacement of fine particles as a function of traffic loading and climatic conditions and a more efficiently designed base and subbase course for specific site conditions.	More reliable and cost-effective base and subbase course support for specific site conditions.
2-1-4. Improvements to Dynamic Modeling of Concrete Pavement Systems for Use in Design and Analysis	$800,000–$1.2 million	A structural model that considers dynamic loading of concrete pavements.	A structural model that considers dynamic loading of concrete pavements that will model traffic loadings more realistically and that can be incorporated into the pavement design guide’s advanced version.
2-1-5. Structural Models for Special New Types of Concrete Pavements and Overlays	$1–$2 million	FEM models that accurately predict structural responses for the slab and supporting layers in selected structural systems.	The ability to consider new and innovative concrete pavement structures for more cost-effective conventional or special design applications.

Problem Statement 2-1-1. Development of Benchmark Problems for Concrete Pavement Structural Models Validation

• Track: 2. Performance-Based Design Guide for New and Rehabilitated Concrete Pavements.
  
  
• Subtrack: 2-1. Design Guide Structural Models.
  
  
• Approximate duration: 4 years.
  
  
• Estimated cost: $500,000–$700,000.

The MEPDG uses a mechanistic model to calculate critical stresses and deflections from traffic and climate factors in JPCP and CRCP. These stresses and deflections are used to predict key distress. The MEPDG development contract (NCHRP 1-37A) could not fully validate these critical stresses and deflections, and concern exists that these stresses and deflections may not be computed accurately by the underlying FEM.⁽¹⁾

Research performed at various locations over the years has compared measured and predicted strains and deflections (e.g., AASHO road test and Minnesota Road Research Project (MnROAD)). Some of the structural models used include Westergaard, JSLAB^®, and ISLAB2000^®. Discrepancies between the calculated and measured strains and deflections have always been evident, but they need additional research attention. Loading speed should be fully considered. The tasks include the following:

1. Identify and document available benchmark solutions of measured stresses (strains) and deflections in the slab and other layers to evaluate the current structural models (including the ISLAB2000^® used in the MEPDG) and determine how closely they predict measured values.(1)
   
   
2. Conduct full-scale experiments and measure structural responses for unavailable but key design situations. Consider future improved structural models (e.g., 3D FEM) in planning and conducting these benchmark solutions.

Benefits: Accurate structural models that improve the performance prediction of concrete pavements.

Products: Data that validate current and future structural models for concrete pavements and accurate structural models that improve the performance prediction of concrete pavements.

Implementation: This research will help establish the accuracy of structural response models. Structural responses are used to calculate the design procedure.

Problem Statement 2-1-2. Improvement of Two-Dimensional and/or Three-Dimensional Structural Models for Jointed Plain Concrete Pavement and Continuously Reinforced Concrete Pavement Used for Reconstruction and Overlays

• Track: 2. Performance-Based Design Guide for New and Rehabilitated
  Concrete Pavements.
  
  
• Subtrack: 2-1. Design Guide Structural Models.
  
  
• Approximate duration: 7 years.
  
  
• Estimated cost: $5–$6 million.

The MEPDG uses the ISLAB2000^® FEM to structurally model JPCP and CRCP that are built as new and used overlays.⁽¹⁾ FEM calculates critical stresses and deflections from traffic and climate factors and then uses them to predict damage and distress. While this is a good state-of-the-art FEM for design use, models must be developed that will more accurately calculate stresses in all types of concrete pavements and rehabilitation situations.

The tasks include the following:

1. Include capability to consider both loading and thermal gradients in a layered system with discontinuities (joints and cracks).
   
   
2. Model all types of concrete pavements and overlays over all types of existing pavement conditions (multiple layers and discontinuities).
   
   
3. Model the effect of all types of bases/subbases and widths on structural responses at joints and other locations.
   
   
4. Model the effect of horizontal restraint (friction) on joint and crack openings and
   structural responses.
   
   
5. Model the effect of separation layers on structural responses.
   
   
6. Improve modeling of subgrade support for new and rehabilitation designs.
   
   
7. Test and validate the FEMs using the benchmark problems developed under this
   design track.

Benefits: Better characterization of design features, interlayer relationships, and material properties, as well as FEMs incorporated into new versions of the pavement design guide.

Products: Improved 2D and 3D FEM that provides significantly improved computation of stresses and deflections for JPCP and CRCP used in reconstruction and as overlays. Additional products include pavement performance prediction models that more accurately predict pavement distress and life for incorporation into a new version of the pavement design guide.

Implementation: FEM will be incorporated into a design procedure as soon as it is completed. It also will be used for parameter and sensitivity studies.

Problem Statement 2-1-3. Development of Model for Erosion Related to Material Properties under Dynamic Wheel Loading

• Track: 2. Performance-Based Design Guide for New and Rehabilitated
  Concrete Pavements.
  
  
• Subtrack: 2-1. Design Guide Structural Models.
  
  
• Approximate duration: 5 years.
  
  
• Estimated cost: $800,000–$1.2 million.

When excess moisture exists in a pavement with an erodible base or underlying fine-grained subgrade material, repeated vehicle loadings typically force the mixture of water and fine material (fines) from beneath the leave slab corner and eject it to the surface through the transverse joint or along the shoulder. This process, commonly referred to as pumping, eventually results in a void below the leave slab corner. Some of the fines that are not ejected are deposited under the approach slab corner, causing the approach slab to rise. This buildup of material beneath the approach corner and the loss of support under the leave corner can cause significant joint faulting, especially for JPCP without dowels. Significant joint faulting increases the life-cycle cost of the pavement through early rehabilitation and vehicle operating costs. Voids also can develop along the edge of CRCP.

The MEPDG level 1 classification of material erodibility is based on the material type and test results from an appropriate laboratory test that realistically simulates erosion beneath a concrete slab.⁽¹⁾ However, suitable tests that would accurately assess erosion under various concrete pavement types are currently unavailable. Levels 2 and 3 rely on strength tests or otherwise inadequate descriptions of base materials. The M-E models relate erosion potential with concrete corner slab deflections. However, this mechanistic parameter only indicates erosion potential indirectly because it does not reflect horizontal movements of the fine particles in the base/subgrade. Moreover, the available erodibility classification methods cannot account mechanistically for the erodibility of the base and subgrade as a function of traffic loading and climatic conditions.

The tasks include the following:

1. Evaluate all available erosion tests and their applicability to mechanistic-based concrete pavement design. Adopt, modify, or develop an erosion test that can consider all types of base and subbase materials used for concrete pavements. Validate the test using partial or full-scale testing in the lab and field.
   
   
2. Develop an erosion model that considers the mechanics of erosion beneath JPCP, CRCP, and other types of concrete pavements for use in an incremental mechanistic concrete pavement design procedure.
   
   
3. Provide detailed guidelines and recommendations for using the test to design in the mechanistic-based design procedure.

Benefits: More reliable and cost-effective base and subbase course support for specific site conditions.

Products: A comprehensive base/subgrade erosion test and model capable of predicting vertical and horizontal displacement of fine particles as a function of traffic loading and climatic conditions and a more efficiently designed base and subbase course for specific site conditions.

Implementation: This problem statement will generate an important, currently missing part of the concrete pavement design guide. The model resulting from this research will be able to be incorporated into the design procedure immediately.

Problem Statement 2-1-4. Improvements to Dynamic Modeling of Concrete Pavement Systems for Use in Design and Analysis

• Track: 2. Performance-Based Design Guide for New and Rehabilitated
  Concrete Pavements.
  
  
• Subtrack: 2-1. Design Guide Structural Models.
  
  
• Approximate duration: 5 years.
  
  
• Estimated cost: $800,000–$1.2 million.

Traffic loadings are almost always moving when they impact the pavement surface. If these loads are moving quickly and the pavement is reasonably smooth, these loads cause deflections that are often less than static. However, as roughness increases, impact loading can develop, which may significantly exceed static loading. Modeling concrete pavement dynamically would provide more realistic loading and speed effects on structural behavior and improve accuracy in predicting key stresses and deflections.

The tasks include the following:

1. Evaluate existing dynamic FEMs and identify those most applicable to concrete
   pavement structures.
   
   
2. Incorporate the ability to consider dynamic loadings into the model using the best available FEM developed under this track.
   
   
3. Test and validate the dynamic FEM using the developed benchmark problems.

Benefits: A structural model that considers dynamic loading of concrete pavements that will more realistically model traffic loadings and that can be incorporated into the pavement design guide’s advanced version.

Products: A structural model that considers dynamic loading of concrete pavements.

Implementation: Dynamic loading impacts pavements every day. Improved understanding may lead to better performance prediction. Results obtained will be implemented immediately into design procedures.

Problem Statement 2-1-5. Structural Models for Special New Types of Concrete Pavements and Overlays

• Track: 2. Performance-Based Design Guide for New and Rehabilitated
  Concrete Pavements.
  
  
• Subtrack: 2-1. Design Guide Structural Models.
  
  
• Approximate duration: 7 years.
  
  
• Estimated cost: $1–$2 million.

Continually seeking improved and more cost-effective concrete pavement designs is important. New and innovative alternative designs have been constructed, and others will be proposed in the future. As an initial step, it is important to have a capable structural model that accurately calculates stress and deformation of these pavement types. This research will expand or modify the latest FEM to model different types of concrete pavements structurally.

Task: Expand or modify FEMs to model the following concrete pavement types and their layered systems beneath the slabs:

• Precast jointed concrete pavement (JCP).
  
  
• Structurally reinforced concrete pavement.
  
  
• Concrete overlays.
  
  
• Other new and innovative types identified.

Benefits: The ability to consider new and innovative concrete pavement structures for more cost-effective conventional or special design applications.

Products: FEM models that accurately predict structural responses for the slab and supporting layers in selected structural systems.

Implementation: The effects of new and innovative designs cannot be established without structural models. These structural models will be implemented into design procedures as soon as the feasibility of special designs is established.

SUBTRACK 2-2. DESIGN GUIDE INPUTS, PERFORMANCE MODELS, AND RELIABILITY

This subtrack develops specific improvements to environmental models, long-term concrete properties, the next generation of traffic models, distress models, and easy-to-use reliability analysis tools. Table 10 provides an overview of this subtrack.

Table 10. Subtrack 2-2 overview.

Problem Statement	Estimated Cost	Products	Benefits
2-2-1. Enhancement and Validation of Enhanced Integrated Climatic Models for Temperature, Moisture, and Moduli	$1–$2 million	A more capable and accurate enhanced integrated climatic model (EICM) for use with concrete pavements to provide detailed hourly temperature, moisture, subdrainage, and other inputs for the incremental design process.	Full and accurate consideration of climatic factors that provide more cost-effective and reliable concrete pavement designs.
2-2-2. Development and Enhancement of Concrete Materials Models for Improved Pavement Design	$5–$6 million	A better understanding of concrete materials models that will be incorporated into current and advanced versions of the pavement design guide, making it more reliable and cost effective.	Better quantification of long-term concrete properties to consider these factors in design more accurately. This research will help determine the impact of various key construction aspects on slab behavior and performance and the concrete fatigue of full-scale slabs under various conditions.
2-2-3. Enhancement and Validation of Traffic Loading Models Unique to Concrete Pavements	$600,000– $1 million	Improved traffic characterization for use in concrete pavement design.	Better characterization of traffic loadings for use in concrete pavement design.
2-2-4. Improved Jointed Plain Concrete Pavement Deterioration Models	$1.5–$2.5 million	Improved and more comprehensive distress and smoothness prediction models for JPCP, including JPCP on low-volume roadways.	Reduced prediction uncertainty, resulting in a more cost-effective design for a given level of reliability for JPCP and improved validation of JPCP design for low-volume roadways.
2-2-5. Improved Continuously Reinforced Concrete Pavement Cracking and Punchout Prediction Models	$1.5–$2.5 million	Improved and more comprehensive distress and smoothness prediction models for CRCP.	Reduced prediction uncertainty, resulting in a more cost-effective design for a given level of reliability for CRCP.
2-2-6. Improved Consideration of Foundation and Subdrainage Models	$1–$1.5 million	An improved and more comprehensive design procedure that considers the base layer, subbase layers, subgrade, and subdrainage of concrete pavements more fully, as well as guidelines that will be implemented into a future version of the pavement design guide.	Improved consideration of the foundation and subdrainage that will be implemented into the pavement design guide to produce more reliable and cost-effective designs.
2-2-7. Identify and Implement New and Practical Ways to Incorporate Reliability into Concrete Pavement Design and Rehabilitation	$3–$5 million	Improved and more comprehensive reliability methodology that considers individual input, model, and other variabilities for concrete pavement mechanistic design.	Improved procedures that will reduce first costs and improve credibility of the mechanistic design approach since design reliability critically affects pavement costs and performance.

Problem Statement 2-2-1. Enhancement and Validation of Enhanced Integrated Climatic Models for Temperature, Moisture, and Moduli

• Track: 2. Performance-Based Design Guide for New and Rehabilitated Concrete Pavements.
  
  
• Subtrack: 2-2. Design Guide Inputs, Performance Models, and Reliability.
  
  
• Approximate duration: 3 years.
  
  
• Estimated cost: $1–$2 million.

EICMs in the MEPDG are a major step toward considering the many climate factors in concrete pavement design.⁽¹⁾ The EICM receives the following hourly data from weather stations: solar radiation, temperature, precipitation, wind speed, and cloud cover. The software then applies the weather data to the pavement section under consideration to predict pavement temperature and moisture at various points within each pavement layer and in the subgrade. These temperatures and moistures serve many purposes, including calculation of stress and curling using temperature gradients through the slab, estimation of layer modulus using moisture contents in unbound materials, estimation of the dynamic modulus of asphalt-bound materials, estimation of the frost line and modulus below and above the line, and computation of the load transfer efficiency (LTE) using joint and crack openings. While EICM is an extremely valuable tool, certain aspects must be improved to support more advanced climatic modeling of concrete pavements.

The tasks include the following:

1. Further validation of moisture contents in unbound materials.
   
   
2. Further validation of temperature gradients and moisture gradients in concrete slabs.
   
   
3. Wider system capabilities to handle subdrainage in 2D or 3D pavement systems.
   
   
4. Further validation of various thermal and hydraulic inputs for various materials.

Benefits: Full and accurate consideration of climatic factors that provide more cost-effective and reliable concrete pavement designs.

Products: A more capable and accurate EICM for use with concrete pavements to provide detailed hourly temperature, moisture, subdrainage, and other inputs for the incremental design process.

Implementation: The EICM is the heart of the design procedure, and any improvements will be implemented immediately.

Problem Statement 2-2-2. Development and Enhancement of Concrete Materials Models for Improved Pavement Design

• Track: 2. Performance-Based Design Guide for New and Rehabilitated
  Concrete Pavements.
  
  
• Subtrack: 2-2. Design Guide Inputs, Performance Models, and Reliability.
  
  
• Approximate duration: 7 years.
  
  
• Estimated cost: $5–$6 million.

Concrete materials properties significantly affect concrete pavement performance. Improving the characterization of slab concrete will allow researchers to more reliably predict pavement performance. This research will address many key aspects of improving concrete materials and construction.

The tasks include the following:

1. Consider in the design stage that several concrete material properties vary over time including strength, modulus, shrinkage, creep, and others. Provide further data on
   these properties.
   
   
2. Determine the effect of construction factors on concrete materials properties in the slab. This would minimally include slab curing, slab zero-stress temperature, built-in curling (thermal gradient through slab as it solidifies), and differential slab shrinkage.
   
   
3. Conduct concrete slab repeated load testing. This would include major studies on full-scale slab fatigue characteristics that consider curling, warping, support, strength, modulus, support conditions, and coefficient of thermal expansion. Accelerated loading facility (ALF) testing would be appropriate for these studies.
   
   
4. Develop fracture models of concrete fatigue for both top-down and bottom-up slab cracking.
   
   
5. Develop new tests for characterizing concrete strength and modulus that better reflect field behavior than current tests.

Benefits: Better quantification of long-term concrete properties to consider these factors in design more accurately. This research will help determine the impact of various key construction aspects on slab behavior and performance and the concrete fatigue of full-scale slabs under various conditions.

Products: A better understanding of concrete materials models that will be incorporated into current and advanced versions of the pavement design guide, making it more reliable and cost effective.

Implementation: The concrete materials models resulting from this research will be immediately incorporated into improved concrete pavement design procedures.

Problem Statement 2-2-3. Enhancement and Validation of Traffic Loading Models Unique to Concrete Pavements

• Track: 2. Performance-Based Design Guide for New and Rehabilitated
  Concrete Pavements.
  
  
• Subtrack: 2-2. Design Guide Inputs, Performance Models, and Reliability.
  
  
• Approximate duration: 3 years.
  
  
• Estimated cost: $600,000–$1 million.

Traffic loading on concrete pavements varies from very low to extremely heavy. A typical concrete pavement located on a major highway could carry 50,000 (on a low-volume road) to more than 200 million (on an urban freeway) heavy trucks over its 30- to 40-year lifetime. Accurately characterizing traffic loadings is critical to good design.

The MEPDG significantly improved traffic loading characterization by considering the full axle spectrum for each type of axle (i.e., single, tandem, tridem, and quads).⁽¹⁾ However, further improvements are needed.

The tasks include the following:

1. Determine the effect of traffic speed on performance.
   
   
2. Determine the critical traffic loadings for fatigue cracking.
   
   
3. Determine how to model tandem, tridem, and quad axles and improve modeling of
   their distribution.
   
   
4. Evaluate the type of loading that contributes to top-down slab cracking where axles are spaced about 10–20 ft apart, and load the slab at each transverse joint, causing a negative cantilever effect with high top-of-slab stresses.

Benefits: Improved characterization of traffic loadings for use in concrete pavement design.

Products: Improved traffic characterization for use in concrete pavement design.

Implementation: The traffic loading models resulting from this research will be immediately incorporated into concrete pavement design procedures.

Problem Statement 2-2-4. Improved Jointed Plain Concrete Pavement Deterioration Models

• Track: 2. Performance-Based Design Guide for New and Rehabilitated
  Concrete Pavements.
  
  
• Subtrack: 2-2. Design Guide Inputs, Performance Models, and Reliability.
  
  
• Approximate duration: 4 years.
  
  
• Estimated cost: $1.5–$2.5 million.

Used in all levels of streets and highways from low to high traffic volumes, JPCP is the most popular type of concrete in the world. This popularity is due to its relative cost effectiveness and its reliability. The JPCP design has significantly improved through increased knowledge over the past several decades.

The tasks include the following:

1. Improve the top-down and bottom-up transverse cracking models for new and rehabilitated pavements developed under the MEPDG.⁽¹⁾ Include models for JPCP designs located on low-volume rural and urban roadways, as well as on higher volume roadways.
   
   
2. Predict crack deterioration. When JPCP cracks, some of these cracks do not deteriorate, while others deteriorate significantly. These deteriorating cracks require maintenance and cause roughness. A study will investigate the causes of crack deterioration and develop models to be used in design that predict crack deterioration. The effects of preventive maintenance on crack deterioration rate also will be studied.
   
   
3. Study longitudinal cracking (fatigue related). Some longitudinal cracking in JPCP could not be explained by traditional fatigue cracking calculations. A major study will determine the circumstances under which fatigue-based longitudinal cracking could occur. The effect of widened slabs also will be investigated.
   
   
4. Improve joint faulting and spalling models for new construction and overlays. The existing models will be considered and improved to model faulting for all design types and model rehabilitation situations needed for design. An improved joint opening/closing model may also be needed. The models should include JPCP designs located on low-volume rural and urban roadways as well as on higher volume roadways.
   
   
5. Develop improved smoothness (International Roughness Index (IRI)) models for JPCP.

Benefits: Reduced prediction uncertainty, resulting in a more cost-effective design for a given level of reliability for JPCP and improved validation of JPCP design for low-volume roadways.

Products: Improved and more comprehensive distress and smoothness prediction models for JPCP, including JPCP on low-volume roadways.

Implementation: The JPCP deterioration models resulting from this research will be incorporated immediately into improved concrete pavement design procedures.

Problem Statement 2-2-5. Improved Continuously Reinforced Concrete Pavement Cracking and Punchout Prediction Models

• Track: 2. Performance-Based Design Guide for New and Rehabilitated
  Concrete Pavements.
  
  
• Subtrack: 2-2. Design Guide Inputs, Performance Models, and Reliability.
  
  
• Approximate duration: 4 years.
  
  
• Estimated cost: $1.5–$2.5 million.

Several States and other countries use CRCP, especially for heavily trafficked highways. In Long-Term Pavement Performance (LTPP) program testing, it has proven to be the smoothest of all pavement types for more than 30 years due to its ability to handle very high traffic loadings over a long period. CRCP design has improved significantly through increased knowledge over the past several decades.

The tasks include the following:

1. Improve the crack spacing, crack width, and crack load deterioration models developed
   under the MEPDG.⁽¹⁾ An improved crack opening/closing model may be needed.
   
   
2. Improve the prediction of edge-top-down structural punchouts developed under
   the MEPDG.⁽¹⁾
   
   
3. Investigate the occurrence of punchouts from the bottom up, especially for widened slab CRCP designs.
   
   
4. Develop an improved smoothness (IRI) prediction model for CRCP.

Benefits: Reduced prediction uncertainty, resulting in a more cost-effective design for a given level of reliability for CRCP.

Products: Significantly improved and more comprehensive distress and smoothness prediction models for CRCP.

Implementation: The CRCP cracking and punchout prediction models resulting from this research will be incorporated immediately into improved concrete pavement design procedures.

Problem Statement 2-2-6. Improved Consideration of Foundation and Subdrainage Models

• Track: 2. Performance-Based Design Guide for New and Rehabilitated Concrete Pavements.
  
  
• Subtrack: 2-2. Design Guide Inputs, Performance Models, and Reliability.
  
  
• Approximate duration: 4 years.
  
  
• Estimated cost: $1–$1.5 million.

The base course, subbase courses, and the subgrade are important to the performance of any type of concrete pavement. Imbedded in the foundation is pavement structure subdrainage, as well as a significant portion of the entire concrete pavement cost. The sublayers affect both the structural aspects (deflection and stress) in the slab and critical load transfer across joints and cracks (e.g., the base layer affects the LTE of the joint or crack). In addition, the friction between the slab and base is important for initiating cracks at the joints, and in CRCP, the transverse shrinkage cracks. Many examples have shown that sublayer and subdrainage failures have led to concrete slab failure. Improvements are needed to produce more reliable and cost-effective sublayer designs for concrete pavement.

The tasks include the following:

1. Identify key practical aspects of sublayers, such as materials and construction that relate to concrete pavement subdrainage, performance, and cost.
   
   
2. Determine how various subgrade situations (from soft wet soils to near-surface bedrock) affect performance and develop improved guidelines for preparing concrete pavement foundations and sublayers.
   
   
3. Develop improved inputs for designing the parameters that characterize concrete pavement sublayers. These would include time-dependent moduli (i.e., seasonal changes), hydraulic permeability, and other parameters.
   
   
4. Develop improved inputs for slab/base friction characteristics of various base layer types.
   
   
5. Determine the impact of JPCP and CRCP on sublayers and subgrade performance using the mechanistic-based design procedure.
   
   
6. Develop guidelines on selection of base types, subbase types, subdrainage, and subgrade treatments to produce cost-effective yet good performance of concrete pavements.
   
   
7. Consider the likelihood and impact of distress propagation and interaction due to cracks in the base course.
   
   
8. Evaluate subdrainage needs for all concrete pavement levels and develop improved impact projections of subdrainage or lack of subdrainage on performance.
   
   
9. Develop new, more reliable, and cost-effective ways to drain concrete pavements.

Benefits: Improved consideration of the foundation and subdrainage that will be implemented into the pavement design guide to produce more reliable and cost-effective designs.

Products: An improved and more comprehensive design procedure that considers the base layer, subbase layers, subgrade, and subdrainage of concrete pavements more fully. Additional products include guidelines that will be implemented into a future version of the pavement design guide.

Implementation: The foundation and subdrainage models resulting from this research will be incorporated immediately into improved concrete pavement design procedures (also see problem statement 2-1-3 on erosion).

Problem Statement 2-2-7. Identify and Implement New and Practical Ways to Incorporate Reliability into Concrete Pavement Design and Rehabilitation

• Track: 2. Performance-Based Design Guide for New and Rehabilitated
  Concrete Pavements.
  
  
• Subtrack: 2-2. Design Guide Inputs, Performance Models, and Reliability.
  
  
• Approximate duration: 7 years.
  
  
• Estimated cost: $3–$5 million.

Reliability is a critical area of design for which little knowledge exists. Nearly everything associated with pavements (as well as most other structures) is variable or uncertain. This includes factors such as traffic loading estimates, climate prediction estimates, subgrade soils along a project, paving materials variations, construction process variations, and design procedure inadequacies. Designers must consider these uncertainties and variations to produce a design with a chance of success greater than 50-50.

The Texas Department of Transportation first incorporated design reliability into pavement design in the early 1970s, and these procedures were used successfully for more than two decades. The 1986 AASHTO Pavement Design Guide made use of similar but expanded concepts to incorporate design reliability into the asphalt and concrete pavement design procedures.⁽⁷⁾ The new mechanistic-based MEPDG incorporated design reliability into the pavement design process differently, using the residual error in the prediction of sections used for calibration.⁽¹⁾

All of these approaches have significant limitations and inadequacies. Design reliability significantly impacts both performance and pavement structure costs. Some feel that the current AASHTO procedures over design for higher levels of traffic because of the large effect of the multiplier on traffic (e.g., design traffic is three to six times the mean estimated traffic). Extensive research has been conducted on the design reliability of other structures such as buildings, retaining walls, foundations, and hydraulic structures. However, little research has been done on pavement design reliability. Therefore, any improvement to the procedure would impact cost and concrete pavements performance significantly.

The tasks include the following:

1. Review how design reliability has been incorporated into various structural design procedures. Identify the most promising approaches and concepts for use in concrete pavement mechanistic design.
   
   
2. Develop a practical procedure for incorporating design reliability into the MEPDG’s mechanistic-based design procedure.⁽¹⁾ This methodology will allow designers to input the means, standard deviations, and distributions of many of the key input variables.
   
   
3. Estimate the magnitudes of variability and uncertainty and their distributions that will be used in the reliability-based design procedure. These estimates will be based on collected data.

Benefits: Improved procedures that will reduce costs and improve credibility of the mechanistic design approach, since design reliability critically affects pavement costs and performance.

Products: Significantly improved and comprehensive reliability methodology that considers individual input, model, and other variabilities for concrete pavement mechanistic design.

Implementation: The results of this research will be incorporated immediately into improved concrete pavement design and rehabilitation procedures for greater reliability.

SUBTRACK 2-3. SPECIAL DESIGN AND REHABILITATION ISSUES

This subtrack addresses the design details from tied shoulders, tie-bars, and pavement preservation and considers better ways to analyze alternative design features using more streamlined computer software. Table 11 provides an overview of this subtrack.

Table 11. Subtrack 2-3 overview.

Problem Statement	Estimated Cost	Products	Benefits
2-3-1. Concrete Pavement Design Aspects Related to Multiple/Additional Lanes	$800,000– $1.5 million	Specific design methodology, guidelines, and standards for tying together multiple traffic lanes and shoulders.	Fewer unexpected incidents of longitudinal cracking that result from tying too many lanes together or widening longitudinal joints that had been left untied.
2-3-2. Characterization of Existing Concrete or Hot Mix Asphalt Pavement to Provide an Adequate Rehabilitation Design	$3.5–$4.5 million	Improved characterization of existing pavements, improved estimates of remaining life that will be useful for selecting from alternative rehabilitations, identification of solutions for overcoming existing poor design and material situations, and improved support for unbonded concrete overlay design.	Proper characterization of the existing pavement critical to reliable and cost-effective rehabilitation design and rehabilitation design improvements to the pavement design guide.
2-3-3. Improvements to Concrete Overlay Design Procedures	$4–$4.5 million	Improved guidelines and design procedures for several types of concrete overlays, including concrete overlays of difficult existing pavements, ultra-thin slab design that includes improved concrete-to-asphalt bonding procedures, improved layering modeling for unbonded concrete overlays, characterization of underlying concrete slab design and condition for unbonded overlays, and improved bonding between thin concrete overlay and existing concrete slabs.	Concrete overlays of difficult existing pavements, ultra-thin slab design including improved concrete-to-asphalt bonding procedures, improved layering modeling for unbonded concrete overlays, characterization of underlying concrete slab design and condition for unbonded overlays, and improved bonding between thin concrete overlay and existing concrete slabs.
2-3-4. Improvements to Concrete Pavement Restoration/ Preservation Procedures	$2–$3 million	Improved guidelines and design procedures for several types of concrete overlays that improve their reliability, viability, and cost effectiveness.	Improved guidelines and design procedures for the several activities involved with restoring and preserving existing concrete pavements, resulting in improved decisionmaking for potential concrete pavement restoration (CPR) projects in terms of selecting needed treatments (such as DBR), predicting remaining life, and further validating CPR as a reliable alternative.
2-3-5. Development of New and Innovative Concrete Pavement Type Designs	$1–$2 million	New and innovative types of concrete pavement and a working design procedure for use and demonstrations of new concrete pavement types performed under track 6.	Improved options to consider for the design and cost effective and reliable concrete pavement designs.
2-3-6. Optimizing Procedure for New Design and Future Maintenance and Rehabilitation Capable of Minimizing Total Life-Cycle Costs, Lane Closure Time, and Other Design Goals over the Range of Design Life	$1–$2 million	A comprehensive system that, for a given design project, analyzes a number of alternative initial designs, future preservation treatments, and rehabilitation options. It also determines the optimum combination to minimize life-cycle costs, initial construction cost, the cost of shoulders and widened slabs, or lane closure time. It also addresses other needs of the designer. Such a system could handle varying design lives from 8 to over 60 years.	New and innovative designs that will improve options to consider for the design and provide more cost-effective and reliable concrete pavement designs.

Problem Statement 2-3-1. Concrete Pavement Design Aspects Related to Multiple/Additional Lanes

• Track: 2. Performance-Based Design Guide for New and Rehabilitated Concrete Pavements.
  
  
• Subtrack: 2-3. Special Design and Rehabilitation Issues.
  
  
• Approximate duration: 3 years.
  
  
• Estimated cost: $800,000–$1.5 million.

There are many design situations where multiple traffic lanes and concrete shoulders are adjacent. For example, a design situation with three lanes in one direction and two tied shoulders on each side would result in a concrete pavement more than 50 ft wide. Also, several critical design decisions must be made regarding the longitudinal joints. The common practice is to tie the shoulders and lanes together with deformed tie-bars, but are they always needed? If needed, what are their proper bar diameters, spacings, and embedment lengths?

Too many tied joints could possibly contribute to longitudinal random cracking. How many is too many for a given design situation? How many lanes/shoulders can be tied together? What should be done if the base course is an unbound aggregate? What should be done if the base course is permeable asphalt? What should be done if the pavement is constructed during wide swings in ambient temperature?

There is not enough research knowledge regarding these issues. This research will consider these questions to develop a design procedure for multiple traffic lanes and adjacent concrete shoulders.

The tasks include the following:

1. Develop an analytical model that accurately calculates the stresses and deformations in concrete pavement slabs when tied together in multiple lanes and shoulders.
   
   
2. Develop a tie-bar design procedure for multiple lanes and shoulders on a variety of
   base courses.
   
   
3. Address key design issues and provide guidelines for adding lanes, widening narrow lanes, and replacing shoulders.
   
   
4. Evaluate the need for longitudinal joint LTE for various design situations.

Benefits: Fewer unexpected incidents of longitudinal cracking that result from tying too many lanes together or widening longitudinal joints that had been left untied.

Products: Specific design methodology, guidelines, and standards for tying together multiple traffic lanes and shoulders.

Implementation: The design methodology, guidelines, and standards resulting from this research will be incorporated immediately into improved concrete pavement design procedures.

Problem Statement 2-3-2. Characterization of Existing Concrete or Hot Mix Asphalt Pavement to Provide an Adequate Rehabilitation Design

• Track: 2. Performance-Based Design Guide for New and Rehabilitated
  Concrete Pavements.
  
  
• Subtrack: 2-3. Special Design and Rehabilitation Issues.
  
  
• Approximate duration: 4 years.
  
  
• Estimated cost: $3.5–$4.5 million.

The United States contains a huge infrastructure of existing highway pavements. Every day, designers grapple with ways to develop an adequate design that will carry traffic reliably over the next design period. To accomplish this task, researchers must characterize or evaluate the existing pavement adequately and overcome its inherent deficiencies with a sufficient rehabilitation design. Several end products related to the characterization of existing concrete or hot mix asphalt (HMA) pavement will result from these research tasks. Improved characterization of existing pavements will be the most significant and valuable accomplishment. Improved estimates of remaining pavement life will be useful for selecting alternative rehabilitations. Identifying and providing solutions to overcome several existing poor design and material situations will be extremely valuable. Finally, improving key unbonded concrete overlay design procedures will lead to greater reliability and cost effectiveness.

The tasks include the following:

1. Develop improved procedures for characterizing an existing concrete or HMA pavement to provide an adequate rehabilitation design.
   
   
2. Develop a procedure for rapidly determining the remaining life of an existing concrete pavement. The procedure should allow a designer to make remaining pavement life determinations by integrating data on current design features, accumulated and future environmental and loading data, data on existing conditions obtained through visual surveys, field and laboratory testing, in-place sensors, and advanced pavement performance modeling techniques. This will help determine the best alternative rehabilitation designs.
   
   
3. Identify the key rehabilitation design issues related to overcoming a poor existing design and materials for rehabilitation.
   
   
4. Develop improved procedures and technology for unbonded concrete overlays:
   
   
5. Determine the effect of the existing concrete slab on unbonded overlay performance.
   
   
6. Identify the interface conditions for various surface preparations and treatments necessary for achieving optimal performance based on field studies of in place pavements.
   
   
7. Develop guidelines for selecting the separation layer that will be used to design unbonded overlays considering the existing pavement condition, type and design of the overlay, climate, and traffic loadings.
   
   
8. Evaluate the effects of interface degradation or improvements over time.

Benefits: Proper characterization of the existing pavement critical to reliable and cost-effective rehabilitation design and rehabilitation design improvements to the pavement design guide.

Products: Improved characterization of existing pavements, improved estimates of remaining life that will be useful for selecting from alternative rehabilitations, identification of solutions for overcoming existing poor design and material situations, and improved support for unbonded concrete overlay design.

Implementation: Good rehabilitation requires good evaluation. The results of this research will be implemented immediately into an improved concrete overlay rehabilitation design procedure.

Problem Statement 2-3-3. Improvements to Concrete Overlay Design Procedures

• Track: 2. Performance-Based Design Guide for New and Rehabilitated
  Concrete Pavements.
  
  
• Subtrack: 2-3. Special Design and Rehabilitation Issues.
  
  
• Approximate duration: 6 years.
  
  
• Estimated cost: $4–$4.5 million.

Reliably designing all types of concrete overlays is essential to highway agencies. However, existing procedures lack a number of capabilities. This research will address a variety of those needs for both bonded and separated concrete overlay designs and for both existing concrete and HMA pavements.

The tasks include the following:

1. Develop guidelines and procedures for designing concrete overlays and widening existing narrow slabs.
   
   
2. Develop reliable design procedures for ultra-thin slabs placed on existing concrete or HMA layers. For this, improved evaluation techniques of the existing pavement and improved bonding and design procedures are needed.
   
   
3. Develop improved layering and jointing models to consider unbonded concrete overlays and the underlying layers.
   
   
4.  
   
   
5. Develop technology to estimate the required design inputs for considering the design and condition of the existing concrete pavement.
   
   
6. Develop improved bonding techniques for bonding concrete layers over existing
   concrete slabs.

Benefits: Concrete overlays of difficult existing pavements, ultra-thin slab design including improved concrete-to-asphalt bonding procedures, improved layering modeling for unbonded concrete overlays, characterization of underlying concrete slab design and condition for unbonded overlays, and improved bonding between thin concrete overlay and existing concrete slabs.

Products: Improved guidelines and design procedures for several types of concrete overlays, including concrete overlays of difficult existing pavements as well as ultra-thin slab design that includes improved concrete-to-asphalt bonding procedures, improved layering modeling for unbonded concrete overlays, characterization of underlying concrete slab design and condition for unbonded overlays, and improved bonding between thin concrete overlay and existing concrete slabs.

Implementation: Concrete overlays must be more cost effective to compete with alternatives. The results of this research will be implemented immediately into concrete pavement design procedures.

Problem Statement 2-3-4. Improvements to Concrete Pavement Restoration/Preservation Procedures

• Track: 2. Performance-Based Design Guide for New and Rehabilitated
  Concrete Pavements.
  
  
• Subtrack: 2-3. Special Design and Rehabilitation Issues.
  
  
• Approximate duration: 5 years.
  
  
• Estimated cost: $2–$3 million.

Many State highway agencies currently apply preservation techniques to all types of pavements, including concrete. As the Nation’s interstate highways age, more effective CPR and preservation techniques have become daily activities for many State highway agencies. The techniques include joint repair, dowel retrofitting, shoulder replacement (including retrofitting with tied concrete), slab replacement, full-depth patching with concrete, grouting and fill of voids, and diamond grinding.

Though several guidelines explain these tasks, very few mechanistic-based procedures evaluate the effectiveness of such repairs in preventing or delaying future distress and its progression. One design procedure that uses mechanistic-based procedures to evaluate and determine the feasibility of CPR is found in the MEPDG.(1)

The tasks include the following:

1. Evaluate the MEPDG mechanistic-based procedures for assessing the effectiveness of JPCP subjected to CPR.(1)
   
   
2. Enhance the MEPDG JPCP procedures and develop new procedures for evaluating CPR performed on other concrete pavement types, such as CRCP and jointed reinforced concrete pavement (JRCP).(1)  At minimum, the procedure should consider existing pavement design features, climatic conditions, traffic loading, existing distress conditions that include materials durability, future loadings data, and advanced M-E modeling to determine future CPR pavement performance based on key performance indicators.
   
   
3. Develop improved guidelines and procedures for designing CPR/preservation projects. These should include improved procedures that assess the window of opportunity for applying preservation techniques to existing concrete pavements.
   
   
4. Develop improved procedures for estimating the remaining life (both structural and functional) of existing concrete pavements so that improved restoration or concrete
   overlay decisions can be made.
   
   
5. Develop enhanced pavement management data to support cost-effective pavement preservation.

Benefits: Improved guidelines and design procedures for the activities involved with restoring and preserving existing concrete pavements, resulting in improved decisionmaking for potential CPR projects in terms of selecting needed treatments (such as DBR), predicting remaining life, and further validating CPR as a reliable alternative.

Products: Improved guidelines and design procedures for several types of concrete overlays that improve their reliability, viability, and cost effectiveness.

Implementation: This research will provide practical technological improvements to CPR that will be implemented immediately into design procedures.

Problem Statement 2-3-5. Development of New and Innovative Concrete Pavement Type Designs

• Track: 2. Performance-Based Design Guide for New and Rehabilitated Concrete Pavements.
  
  
• Subtrack: 2-3. Special Design and Rehabilitation Issues.
  
  
• Approximate duration: 5 years.
  
  
• Estimated cost: $1–$2 million.

JPCP is the world’s most widely constructed pavement. Many States and other countries have also constructed CRCP, which seems to be gaining popularity. JPCP has been constructed extensively in the United States, but serious problems with joints and intermediate panel cracking have halted their construction in all States and foreign countries. JPCP and CRCP pavement types also have problems and limitations. More innovative, cost-effective, and reliable design alternatives need to be explored.

The tasks include the following:

1. Conduct a study to explore new and innovative options for concrete pavement designs. This study will involve performing a literature search and contacting as many agencies as possible around the world to investigate the latest innovative designs.
   
   
2. Evaluate these candidates for feasibility and recommend the most promising. Consider the following as a minimum:
   
   
   • Thin slab replacement for existing pavements: Many existing concrete or HMA pavements have thicknesses of 8 to 10 inches. A cost-effective solution is to remove this layer and replace it with a relatively thin concrete slab design especially suited for heavy traffic. Design procedures to accomplish this reliably and in a cost-effective manner
     are needed.
     
     
   • Design innovations for JPCP and CRCP: Design innovations should optimize the structural and material design of these pavements (e.g., trapezoidal cross sections).
     
     
   • Precast JCP design: These are being constructed at several projects, and a major research and development effort is underway to improve their design and construction. Placement speed is their main advantage, with no further curing time required.
     
     
   • Concrete overlays, reinforcement, and special surfacing designs: This includes two or more layers of paving materials (concrete, reinforcement, special materials, etc.) bonded together. Typical examples include two-layer construction (wet on wet) using layers with different properties, CRCP with special two-layer reinforcement, and special epoxy resin concrete surfacing materials.
     
     
   • Structurally reinforced concrete pavement design, including CRCP: A few of these pavements have been constructed in places such as Brazil and Columbia. One design built in Brazil uses two layers of steel in a slab placed on a prepared base course.
     Another design built in Columbia is essentially a reinforced concrete bridge deck with longitudinal reinforced concrete beams placed in trenches (the slab is not on grade). The Netherlands has developed a similar system.
     
     
   • Prestressed post-tensioned concrete pavements: Several of these have been built in the United States and abroad over the past 30 years. However, the expansion joints often have failed and required maintenance.
     
     
3. Develop design procedures for the most promising type of concrete pavements using the existing mechanistic-based procedure as much as possible.

Benefits: Improved options to consider for the design as well as cost-effective and reliable concrete pavement designs.

Products: New and innovative types of concrete pavement, a working design procedure for use, and demonstrations of new concrete pavement types performed under tracks 6 and 8.

Implementation: The new and innovative concrete pavement types will be demonstrated and evaluated under tracks 6 and 9 and incorporated into a future version of the pavement design guide.

Problem Statement 2-3-6. Optimizing Procedure for New Design and Future Maintenance and Rehabilitation Capable of Minimizing Total Life-Cycle Costs, Lane Closure Time, and Other Design Goals over the Range of Design Life

• Track: 2. Performance-Based Design Guide for New and Rehabilitated
  Concrete Pavements.
  
  
• Subtrack: 2-3. Special Design and Rehabilitation Issues.
  
  
• Approximate duration: 7 years.
  
  
• Estimated cost: $1–$2 million.

The MEPDG evaluates a trial design provided by the designer.⁽¹⁾ The proposed design must make several trial runs before an acceptable design is established, and this is only for the first performance period. The design procedure does not consider future rehabilitations, nor does it provide optimization procedures to minimize life-cycle costs or even first costs. An optimization procedure to be incorporated into the current and future versions of the pavement design guide is needed.

The tasks include the following:

1. Develop design procedure concepts that consider multiple initial trial designs and multiple optional rehabilitation alternatives and then select designs from among the initial ones that optimize (i.e., minimize or maximize) a desired factor. This factor could be life-cycle costs, initial construction costs, future rehabilitation costs, and user delay costs, among others.
   
   
2. Design procedure concepts should be developed for shoulders, tied shoulders, and alternative shoulder materials.
   
   
3. Develop software to accomplish the optimization described above in the first task.
   
   
4. Validate the software using several actual projects provided by State highway agencies.

Benefits: New and innovative design options that will improve options to consider for the design and provide more cost-effective and reliable concrete pavement designs.

Products: A comprehensive system that, for a given design project, analyzes a number of alternative initial designs, future preservation treatments, and rehabilitation options. The system also determines the optimum combination to minimize life-cycle costs, initial construction cost, the cost of shoulders and widened slabs, and lane closure time. It also addresses other needs of the designer. Such a system could handle varying design lives from 8 to over 60 years.

Implementation: Current mechanistic-based procedures in the MEPDG do not optimize.(1) This capability is needed and will be implemented into design procedures immediately.

SUBTRACK 2-4. IMPROVED MECHANISTIC DESIGN PROCEDURES

This subtrack will be used to develop the new generation design procedure and a comprehensive database of performance data needed for calibration and validation. Table 12 provides an overview of this subtrack.

Table 12. Subtrack 2-4 overview.

Problem Statement	Estimated Cost	Products	Benefits
2-4-1. Incremental Improvements to Mechanistic-Empirical Pavement Design Guide Procedures	$1.5–$2.5 million	An improved and implementable design procedure for new and rehabilitated JPCP and CRCP designs.	A significantly improved pavement design guide that better considers many of its aspects and several new aspects of pavement design, as well as new and rehabilitated designs that are more reliable and cost effective.
2-4-2. New Mechanistic-Empirical Pavement Design Guide Procedures for Paradigm Shift Capabilities	$2–$4 million	New generation pavement design procedures that consider many improvements and new pavement design aspects as well as new and rehabilitated designs that are more reliable and cost effective.	An advanced paradigm shift in integrated concrete pavement design procedures for new and rehabilitated JPCP, CRCP, and other selected designs.

Problem Statement 2-4-1. Incremental Improvements to  Mechanistic-Empirical Pavement Design Guide Procedures

• Track: 2. Performance-Based Design Guide for New and Rehabilitated Concrete Pavements.
  
  
• Subtrack: 2-4. Improved Mechanistic Design Procedures.
  
  
• Approximate duration: 8 years.
  
  
• Estimated cost: $1.5–$2.5 million.

The initial MEPDG, delivered to NCHRP in 2004 after 6 years of development, represents a paradigm shift in design capabilities.⁽¹⁾ AASHTOWare^® released DARWin-ME^TM in 2011. Nevertheless, many aspects of these products still require incremental improvements before the guide meets the concrete pavement design goal that aims for new and rehabilitated designs to be reliable, economical, constructible, and maintainable throughout their design life and to meet or exceed the multiple needs (in highways, urban streets, low-volume roads, and special applications such as tunnels and ports) of the traveling public, taxpayers, and the owning highway agencies. Achieving this goal will require incorporating the results from each of the research studies into the pavement design guide.

The tasks include the following:

1. Improve the FEM neural nets to consider more design and material features (e.g., thinner slabs and better layering capabilities, especially for concrete overlay design).
   
   
2. Develop better traffic characterization procedures, including loadings for top-down cracking and truck speed.
   
   
3. Predict temperature and moisture more accurately.
   
   
4. Incorporate improved base erosion models.
   
   
5. Improve JPCP and CRCP distress prediction models.
   
   
6. Improve JPCP and CRCP IRI prediction models.
   
   
7. Improve sublayer design of base, subbase, subgrade, and particularly subdrainage.
   
   
8. Incorporate an improved design reliability approach.
   
   
9. Improve the characterization of existing concrete and HMA pavements for use in concrete rehabilitated design.
   
   
10. Improve CPR procedures.
    
    
11. Improve concrete overlay design procedures.
    
    
12. Implement design guidelines and procedures related to multiple lanes, including those related to tie-bar design and the number of lanes/shoulders to tie together.
    
    
13. Comprehensively calibrate the models using data collected from the ALFs and long-term test sections developed under track 9.
    
    
14. Validate studies with several State highway agencies.

Benefits: A significantly improved pavement design guide that better considers many of its aspects and several new aspects of pavement design, as well as new and rehabilitated designs that are more reliable and cost effective.

Products: An improved implementable design procedure for new and rehabilitated JPCP and CRCP designs.

Implementation: Many States and local governments will use this new pavement design guide. It can be improved incrementally.

Problem Statement 2-4-2. New  Mechanistic-Empirical Pavement Design Guide Procedures for Paradigm Shift Capabilities

• Track: 2. Performance-Based Design Guide for New and Rehabilitated Concrete Pavements.
  
  
• Subtrack: 2-4. Improved Mechanistic Design Procedures.
  
  
• Approximate duration: 8 years.
  
  
• Estimated cost: $2–$4 million.

This research will develop an advanced version of the pavement design guide that includes major steps forward from the incrementally developed procedures in problem statement 2-4-1. The new, more fully mechanistic-based procedures will require several years to develop (extending to the end of the 10-year period). The goal is to ensure that new and rehabilitated designs for concrete pavement will be more reliable, economical, constructible, and maintainable throughout their design life and meet or exceed the multiple needs (in highways, urban streets, low-volume roads, and special applications such as tunnels and ports) of the traveling public, taxpayers, and the owning highway agencies. Achieving this goal will require incorporating the results from each of the research studies into the pavement design guide. The result will be a paradigm shift in 3D FEM, reliability control, incremental improvements, and advanced capabilities in layering, joints, reinforcement, and long-life design.

The tasks include the following:

1. Incorporate 3D structural FEMs into the design procedure.
   
   
2. Consider implementing the dynamic FEM structural model into the design procedure.
   
   
3. Incorporate a more accurate integrated climatic model for temperature and moisture.
   
   
4. Develop new concrete materials characterization tests, including fatigue damage, strength, modulus, and many other inputs.
   
   
5. Incorporate more accurate long-term changes in material properties (e.g., concrete strength, modulus, shrinkage, and creep).
   
   
6. Predict key distress types in JPCP, CRCP, and other selected pavement types using a more intense incremental damage accumulation measurement (e.g., hourly over the entire design period).
   
   
7. Improve smoothness prediction models for JPCP and CRCP.
   
   
8. Model other functional surface characteristics, such as noise, friction, and spray, as available. This task will link to track 4.
   
   
9. Include optimization capability to give the designer the tools to minimize life-cycle costs or maximize smoothness over the design life.
   
   
10. Improve sublayer design of the base, subbase, subgrade, and particularly subdrainage.
    
    
11. Incorporate an improved design reliability approach.
    
    
12. Comprehensively calibrate the models using data collected from the ALFs and long-term test sections developed under track 9.
    
    
13. Validate studies with many State highway agencies.

Benefits: An advanced paradigm shift in integrated concrete pavement design procedures for new and rehabilitated JPCP, CRCP, and other selected designs.

Products: New generation pavement design procedures that consider many improvements and new pavement design aspects, as well as more reliable and cost-effective new and rehabilitated designs.

Implementation: This research will result in a paradigm shift in pavement design that will produce technology needed to deal with critical problems years from now.

SUBTRACK 2-5. DESIGN GUIDE IMPLEMENTATION

This subtrack addresses implementing the new pavement design guide. Table 13 provides an overview of this subtrack.

Table 13. Subtrack 2-5 overview.

Problem Statement	Estimated Cost	Products	Benefits
2-5-1. Implementation of the Mechanistic-Empirical Pavement Design Guide	$2–$3 million	Strong technology transfer to the workforce concerning the design of new and rehabilitated concrete pavements through workshops, conferences, and Web-based personnel training.	A workforce with the basic knowledge and understanding needed to design concrete pavements and rehabilitation projects using the design procedure properly.

Problem Statement 2-5-1. Implementation of the Mechanistic-Empirical Pavement Design Guide

• Track: 2. Performance-Based Design Guide for New and Rehabilitated Concrete Pavements.
  
  
• Subtrack: 2-5. Design Guide Implementation.
  
  
• Approximate duration: 10 years.
  
  
• Estimated cost: $2–$3 million.

Implementing a mechanistic-based design procedure fundamentally changes the way concrete pavement design is performed. Designers must develop additional skills in areas such as structural analysis, material characterization, local calibration, software usage, and existing pavement characterization. Successful implementation will require thousands of pavement designers to be extensively trained over a period of several years. Hands-on workshops, online training tools, and national workshops can accomplish this task.

The tasks include the following:

1. Develop and present workshops dealing with many aspects of the mechanistic-based
   design process (structural modeling, materials characterization, distress and IRI prediction, overlays, restoration, optimization, traffic, climate, local calibration, etc.).
   
   
2. Develop Web-based training in mechanistic-based design.
   
   
3. Organize national workshops and conferences on mechanistic design.
   
   
4. Organize national conferences and workshops where States and other highway agencies share their findings on the mechanistic design process.
   
   
5. Develop Web-based training tools.

Benefits: A workforce with the basic knowledge and understanding needed to design concrete pavements and rehabilitation projects using the design procedure properly.

Products: Strong technology transfer to the workforce concerning the design of new and rehabilitated concrete pavements through workshops, conferences, and Web-based personnel training.

Implementation: This research will result in technology sharing.