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

TRACK 10. CONCRETE PAVEMENT FOUNDATIONS AND DRAINAGE

TRACK 10 OVERVIEW

This track addresses foundations and drainage elements of concrete pavements. It has been long established that principal components of a long-life concrete pavement include a uniform foundation and proper measures taken for drainage. Given the sheer variety of potential conditions that can be present on any given job (e.g., soil type), there is no “one size fits all” solution. This track explores research and technology related to these important topics, with a particular emphasis on tasks that can be readily applied in a site-specific manner.

The research in this track will determine and address both foundations and drainage aspects of concrete pavements, particularly factors such subgrade, subbase, and base construction, as well as subsurface and surface drainage. It includes measurement design and construction methods as well as measurement techniques.

The following introductory material summarizes the goal and objectives for this track and the gaps and challenges for its research program. A table is included to show an overview of the subtracks and problem statements in the track. 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 10 Goal

The research in this track will provide the pavement engineer with the tools to better design, construct, and evaluate foundations and drainage systems for concrete pavements.

Track 10 Objectives

The track 10 objectives are as follows:

1. Expedite and improve the quality of pavement foundations, particularly on projects with expedited construction.
   
   
2. Identify rapid measurement technologies that can gauge the quality of a concrete pavement foundation.
   
   
3. Improve the understanding of pavement subsurface drainage and its effect on design.
   
   
4. Identify advanced equipment capable of automated subdrain installation.
   
   
5. Identify rapid measurements for surface texture and the impact it can have on
   surface drainage.

Track 10 Research Gaps

The track 10 research gaps are as follows:

• Concrete pavement foundations remain a difficult topic, largely due to the variability that is commonly experienced in the field. From a modeling perspective, a large reliability level is commonly selected to partially compensate for anticipated variability.
  
  
• Measures to gather real-time field information about concrete pavement foundations and drainage remain allusive. While there have been recent advancement, namely with intelligent compaction and real-time profiling, limitations remain in these technologies.

Track 10 Research Challenges

The track 10 research challenges are as follows:

• Overcome obstacles to improved methods to design and constructing concrete pavement foundations and drainage systems.
  
  
• Demonstrate technology that can be used to evaluate the quality and effectiveness of concrete pavement foundations and drainage.

Research Track 10 Estimated Costs

Table 56 shows the estimated costs for this research track.

Track 10 Organization: Subtracks and Problem Statements

Track 10 problem statements are grouped into the following two subtracks:

• Subtrack 10-1. Concrete Pavement Foundations.
  
  
• Subtrack 10-2. Concrete Pavement Drainage.

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 10-1. CONCRETE PAVEMENT FOUNDATIONS

This subtrack will develop and evaluate technologies related to concrete pavement foundations. Table 57 provides an overview of this subtrack.

Problem Statement 10-1-1. Concrete Pavement Support Sensing

• Track: 10. Concrete Pavement Foundations and Drainage.
  
  
• Subtrack: 10-1. Concrete Pavement Foundations.
  
  
• Approximate duration: 5 years.
  
  
• Estimated cost: $1–$2 million.

The support structure beneath concrete pavements significantly affects pavement design characteristics such as thickness, joint spacing, and mix design. Unfortunately, when most pavements are designed, the variability of the supporting structure along the length of the pavement can be significant. Automated nondestructive support-sensing devices would allow the support structure to be assessed continuously along the length of the pavement during the paving operation. Support-sensing devices could be fixed to the paving equipment to determine the stiffness of the support structure at the time of placement and as the paving operation progresses. Automated support-sensing devices could send support information to automated batching and paving equipment, causing the batching equipment to adjust the paving mix or the paver to adjust slab thickness or load transfer (joint spacing) automatically.

The tasks include the following:

1. Identify existing nondestructive support-sensing devices.
   
   
2. Modify existing devices or develop new devices that continuously monitor pavement support layers.
   
   
3. Integrate support-sensing devices into the paving operation to make adjustments automatically.
   
   
4. Validate support-sensing equipment on actual paving projects.
   
   
5. Develop recommendations for deploying support-sensing equipment on paving projects.

Benefits: Automatic adjustments to the mix design, slab thickness, and joint spacing during construction, resulting from continuous monitoring of pavement support in front of the paving operation and high-quality pavements constructed precisely for the support over which they are placed.

Products: Devices for measuring pavement support during construction.

Implementation: This work will result in automated support-sensing equipment that can measure pavement support continuously during construction. This problem statement is linked to problem statement 3-2-5.

Problem Statement 10-1-2. Concrete Pavement Smoothness Sensing

• Track: 10. Concrete Pavement Foundations and Drainage.
  
  
• Subtrack: 10-1. Concrete Pavement Foundations.
  
  
• Approximate duration: 4 years.
  
  
• Estimated cost: $1–$2 million.

Profilographs and inertial profilers are the equipment most commonly used to measure pavement smoothness, providing information to the contractor after placing concrete pavement. While this is a fast way to provide smoothness information, real-time smoothness-measuring devices that can be mounted to slipform machines or a trailing construction bridge are desirable.

The same equipment that is used for real-time concrete pavement profiling can also be used to profile the grade prior to placement.

This research is linked to problem statement 3-2-9 for developing a real-time smoothness-measuring device for concrete pavements. Evaluating the accuracy of the smoothness-measuring device will be necessary to demonstrate its accuracy relative to the profilograph or inertial profiler. In addition, a manual describing the testing equipment and indexing procedure should be developed to implement this equipment and procedure.

The tasks include the following:

1. Identify real-time smoothness-measuring devices.
   
   
2. Adapt the smoothness-measuring devices to evaluate concrete pavement foundation construction.
   
   
3. Develop a system that combines the smoothness measurements with software that automatically calculates relevant metrics for the profile of the grade.
   
   
4. Validate the smoothness measurements on an actual paving project.
   
   
5. Develop recommendations for deploying the smoothness-sensing equipment during the paving operation.

Benefits: Pavement foundation profiling can allow surface deviations to be corrected more readily.

Products: Foundation (grade) smoothness-sensing equipment.

Implementation: This work will result in smoothness-sensing equipment that can be adapted to foundation construction operations. This problem statement is linked to problem statement 3-2-9.

Problem Statement 10-1-3. Rapid Subgrade/Subbase Stabilization

• Track: 10. Concrete Pavement Foundations and Drainage.
  
  
• Subtrack: 10-1. Concrete Pavement Foundations.
  
  
• Approximate duration: 5 years.
  
  
• Estimated cost: $1–$2 million.

One of the problems with fast-track paving (i.e., overnight construction using fast-setting/high-early strength or precast concrete) is stabilizing the existing base material. The pavements being replaced have often deteriorated due to problems with the base material, such as pumping or swelling, resulting in voids beneath the pavement. Using conventional paving techniques, the base material can be replaced or treated (cement/lime/asphalt stabilization) to mitigate these problems. Unfortunately, most existing stabilization techniques cannot be completed in a short (e.g., overnight) construction window because many materials currently used for stabilization cannot be used for overnight stabilization processes. Therefore, research should develop rapid base stabilization and restoration techniques that can be completed within short construction windows. This may require new equipment for rapid stabilization or even new materials. The techniques developed should be able to be incorporated into a one pass pavement removal and replacement operation that uses high-early strength or precast concrete.

The tasks include the following:

1. Identify existing stabilization materials and techniques.
   
   
2. Evaluate existing stabilization materials and techniques for their applicability to rapid stabilization (i.e., overnight and one-pass operations).
   
   
3. Work with contractors and industry representatives to modify or develop new equipment and materials for rapid stabilization.
   
   
4. Work with contractors and owner-agencies to develop pilot studies that use rapid stabilization techniques and materials.

Benefits: Rapid subgrade/subbase stabilization that will allow subgrade/subbase support to be repaired and restored before placing new pavement in a short construction window.

Products: New techniques and equipment for rapid subgrade/subbase stabilization.

Implementation: This research will result in new techniques, equipment, and/or materials for rapid stabilization. This problem statement is linked to problem statement 5-4-1.

SUBTRACK 10-2. CONCRETE PAVEMENT DRAINAGE

This subtrack will develop and evaluate technologies related to concrete pavement drainage. Table 58 provides an overview of this subtrack.

Problem Statement 10-2-1. Development of Model for Erosion Related to Material Properties under Dynamic Loading

• Track: 10. Concrete Pavement Foundations and Drainage.
  
  
• Subtrack: 10-2. Concrete Pavement Drainage.
  
  
• 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. In addition, some of the fines that are not ejected are deposited under the approach slab corner, causing the approach slab to rise. Combined, 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 can also develop along the edge of a 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 indirectly indicates erosion potential 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.
   
   
2. Adopt, modify, or develop an erosion test that can consider all types of base and subbase materials used for concrete pavements and validate the test using partial or full-scale testing in the lab and field.
   
   
3. 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.
   
   
4. 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 as well as 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, and 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. This problem statement is linked to problem statement 2-1-3.

Problem Statement 10-2-2. Improved Consideration of Foundation and Subdrainage Models

• Track: 10. Concrete Pavement Foundations and Drainage.
  
  
• Subtrack: 10-2. Concrete Pavement Drainage.
  
  
• 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 extremely 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 (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 and develop guidelines on selection of base types, subbase types, subdrainage, and subgrade treatments to produce cost-effective yet good performance of concrete pavements.
   
   
6. Consider the likelihood and impact of distress propagation and interaction due to cracks in the base course.
   
   
7. Evaluate subdrainage needs for all concrete pavement levels and develop improved impact projections of subdrainage or lack of subdrainage on performance and 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 and 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. This problem statement is linked to problem statement 2-2-6 (also see problem statement 10-2-1 on erosion).

Problem Statement 10-2-3. Automated Subdrain Installation in Concrete Pavement Construction

• Track: 10. Concrete Pavement Foundations and Drainage.
  
  
• Subtrack: 10-2. Concrete Pavement Drainage.
  
  
• Approximate duration: 3 years.
  
  
• Estimated cost: $1–$2 million.

While certain regions of the United States require pavement subdrains, installing these subdrains is often costly and time consuming. Research is needed to explore ways to install subdrains quickly and efficiently during the paving operation. Ideally, automated installation equipment would install the subdrains immediately in front of the paving operation, eliminating the need for two separate construction processes and additional construction time. Subdrain installation would thus be a one-pass operation that includes excavation, drain installation, and backfilling.

The tasks include the following:

1. Identify typical subdrain specifications required by owner-agencies and viable new subdrain specifications.
   
   
2. Work with contractors and industry representatives to develop automated subdrain installation equipment that could be completed in one pass in front of the paving operation.
   
   
3. Work with owner-agencies and contractors to develop pilot projects that demonstrate automated subdrain installation.

Benefits: Automated subdrain installation that permits the process to be completed in a single pass immediately in front of the paver, thus expediting construction.

Products: New techniques and equipment for automated subdrain installation.

Implementation: This work will result in new techniques and/or equipment for rapid automated subdrain installation in concrete pavement construction. This problem statement is linked to problem statement 5-4-2.

Problem Statement 10-2-4. Concrete Pavement Texture (Skid Resistance and Splash/Spray Sensing)

• Track: 10. Concrete Pavement Foundations and Drainage.
  
  
• Subtrack: 10-2. Concrete Pavement Drainage.
  
  
• Approximate duration: 6 years.
  
  
• Estimated cost: $500,000–$1 million.

For a pavement foundation, surface texture is used to improve friction (skid resistance). However, reducing splash and spray also must be considered because these can affect driver visibility. Predicting both skid resistance and splash/spray potential during pavement construction can ensure that an adequate and safe surface texture is applied. Because skid resistance and splash/spray potential are difficult to measure or quantify on fresh concrete surfaces, surface texture (type and depth), skid resistance, and splash/spray potential may need to be correlated. Measuring surface texture properties during construction will allow the contractor to adjust the paving equipment to improve surface texture and possibly correct still-plastic in place concrete. Surface texture sensing equipment could be mounted on the paving train immediately behind the finishing and texturing processes to determine texture properties in real time. The sensing equipment would provide instant results for a large enough section of pavement to indicate the whole surface adequately.

The tasks include the following:

1. Identify surface texture measurement equipment/techniques that can be used on fresh (plastic) concrete to determine skid resistance and splash/spray potential.
   
   
2. Identify correlations between surface texture measurements, skid resistance, and splash/spray potential.
   
   
3. Modify existing equipment or develop new sensing equipment that measures surface texture properties on fresh concrete.
   
   
4. Develop necessary correlations between surface texture properties, skid resistance, and splash/spray potential.
   
   
5. Validate surface texture measurement equipment on actual paving projects.
   
   
6. Develop recommendations for deploying surface texture sensing equipment.

Benefits: Continuously monitored surface texture, permitting real-time prediction of skid resistance and splash/spray potential; automatic adjustments to finishing and texturing processes to achieve the desired skid resistance and splash/spray characteristics, resulting in as-constructed pavements that meet surface texture requirements without the need for additional texturing measures.

Products: Equipment for predicting skid resistance and splash/spray potential.

Implementation: This work will result in equipment that can predict the skid resistance and splash/spray potential of fresh concrete pavement. This problem statement is linked to problem statement 3-2-10.