Redesigning Pavement Rehabilitation Design

Much of the highway infrastructure was originally constructed on green fields where relatively little information existed on subsurface conditions, drainage paths, locally available materials, traffic projections, etc. A great deal of effort was expended in the exploration of existing conditions, soil sampling and testing, materials characterization, and pavement design ahead of construction. The integration of this information along with low to moderate levels of traffic loading was largely responsible for the initial success of the nation’s highways.

For the past 30 to 40 years, highway construction has been centered around maintenance and rehabilitation activities. Simultaneously, departments’ of transportation (DOT) operating budgets have been reduced, the nature and cost of the materials used in road construction have increased, overall traffic volumes and commercial vehicle volumes have dramatically increased, and the use of consultants in design and construction has become more prevalent. In the meantime, our methods for identifying and designing remedies for pavement failures have been slow to evolve although there is an array of new tools available to investigate subsurface problems and isolate the areas in which they occur.

This research project is expected to produce a comprehensive approach to the identification of pavement distresses. The approach will employ mobile technologies to investigate surface and subsurface conditions, identify different types and levels of remedies based upon the data collected, and determine if a localized or project-wide repair or rehabilitation is needed. It is expected that the resulting information could be used within the Pavement ME Design software to evaluate the structural adequacy of existing pavements and rehabilitation alternatives.

The objectives of this research are:

1. Review current state of mobile/nondestructive pavement evaluation technologies (GPR, FWD, LIDAR, digital image processing/analysis methods, etc.) to provide information for the design of rehabilitation projects.

2. Provide guidance on calibrating and deploying equipment and collecting and organizing data.

3. Provide guidance on data analysis and interpretation to identify non-uniform conditions and the type and level of investigations needed for further definition of the conditions.

4. Provide guidance on integration of information for project-level decisions regarding repairs, structural design, construction costs, and performance.

Currently, many rehabilitation design decisions are made on the basis of incomplete information which carries two dangers: 1) subsurface conditions that come to light during construction causing redesign, delays, and change orders and 2) subsurface conditions that are not caught during construction, which lead to early failure. While some of the equipment mentioned can be expensive and there are additional personnel costs in their deployment, the benefits of getting a better design far outweigh the costs.

The engineering investigation of candidate sections for pavement rehabilitation are sometimes superficial as many of the decisions are based solely upon pavement rating scores from visual surveys and pavement roughness measurements. While these serve important functions in defining the condition of the roadway and providing clues as to the causes of deterioration, there should be a more thorough investigation to examine subsurface conditions. This will help improve decisions regarding the scope and design of rehabilitation. However, thorough investigations of subsurface conditions are often not conducted due to various reasons such as minimizing exposure of personnel to traffic, lack of personnel to carry out the testing, expense of data collection and analysis, etc. The means for using technology to overcome these concerns exist and can be used to characterize roadway conditions with minimal risks. Some examples of tools and their applications are discussed below.

The falling weight deflectometer (FWD) has been in use since the 1980s and has proven to be reliable in assessing the structural condition of pavements. Although rolling deflectometers have been developed and used in some instances as discussed below, the FWD continues to be the workhorse in structural evaluation. While it provides crucial information, the FWD can be made more powerful when it is combined with information from a ground penetrating radar (GPR).

GPR has been in general use since the 1990s to investigate pavement issues such as layer thicknesses, subsurface wet zones, layer delamination, and layer densities (GFS, 1992; Scullion et al., 1996; Kassem et al., 2016; Dai and Yan, 2014). Layer thickness information is crucial to the accurate interpretation of FWD data, as the in-place layer depths and as-built drawings can sometimes differ substantially. Detection of wet zones in the pavement profile (e.g., between granular base and asphalt layers) will also help explain areas of high pavement deflections, and point to the need to improve drainage.

Drainage conditions are crucial to the performance of pavements, and while roadways are originally constructed with systems of well-designed ditches, culverts, and detention ponds, the surrounding landscape and land use can cause the flow of groundwater to change over time. Gurganus et al. (2017) have demonstrated the use of light detection and ranging (LIDAR) equipment for rapidly assessing roadway drainage characteristics and determining corrections needed in the design of slopes, ditches, and underdrain systems ahead of rehabilitation efforts. This information, in addition to the relevant GPR data, can be used to design improved drainage and mitigate subsurface moisture conditions.

The technologies discussed are all in various states of usage in the U.S. and serve as examples of how valuable information can be gathered rapidly and nondestructively for the purposes of pavement rehabilitation design. Identifying localized distress which may need more extensive repair ahead of design will allow engineers to more realistically design and plan for the project rather than discovering hidden conditions at the time of construction. An example of how these technologies can be used in concert is found in Maser et al. (2017). A deflectometer moving at highway speed and ground penetrating radar were used to obtain a combination of pavement layer moduli and thicknesses to perform a structural analysis of the East Idaho Loop Corridor (EILC). As a part of this effort, the team correlated the traffic speed deflectometer (TDS) with the falling weight deflectometer (FWD) measurements and verified GPR layer thickness measurements with roadway core data. They were able to divide the roadway into segments based upon the remaining life of the pavement to improve project planning for future rehabilitation.

Dai, S. and Q. Yan (2014) Pavement Evaluation Using Ground Penetrating Radar. Proceedings. Geo-Shanghai 2014. American Society of Civil Engineers. Reston. pp. 222-230.

Geotechnical Society of Finland (GFS) (1992) Ground Penetrating Radar

Gurganus, C., N. Gharaibeh, and T. Scullion (2017) Case Study on the Use of Mobile Lidar to Produce Preliminary Drainage Design. Transp. Res. Rec. No. 2655. Transportation Research Board. Washington, DC. pp. 82-90.

Kassem, E., A. Chowdhury, T. Scullion, and E. Masad (2016) Application of Ground-Penetrating Radar in Measuring the Density of Asphalt Pavements and Its Relationship to Mechanical Properties. Int’l. Jn. of Pavement Engineering. Vol. 16, No. 6. Taylor and Francis. pp. 503-516.

Scullion, T., C. Lau, T. Saarenketo (1996) Performance Specifications of Ground Penetrating Radar. Proceedings. 6th Int’l. Conference on Ground Penetrating Radar. Sendai, Japan. pp. 341-346.

Saarenketo, T. (2008) Ground Penetrating Radar. Chapter 13. Ground Penetrating Radar: Theory and Application. Harry M. Jol, ed. Elsevier.

Maser, K., P. Schmalzer, W. Shaw, and A. Carmichael (2017) Integration of Traffic Speed Deflectometer and Ground Penetrating Radar for Network-Level Roadway Structure Evaluation. Transp. Res. Rec. No. 2639. Transportation Research Board. Washington, DC. pp. 55-63.

These objectives would be met through four broad tasks:

1. Identify useful technologies for pavement surveys.

2. Provide an assessment of pavement evaluation tools for accuracy and limitations.

3. Develop decision making process for selecting the appropriate array of pavement evaluation tools and testing frequencies for specific projects.

4. Demonstrate effectiveness of pavement evaluation tools on actual rehabilitation projects.

Various districts within the Texas Department of Transportation have employed this approach for the analysis of roadways in the energy sectors. This combined information has allowed them to make better design decisions without having to subject personnel to undue risks while collecting the data.

As mentioned above, this type of an approach was used by Idaho to design the rehabilitation strategy for the EILC. This project would take these tools and provide guidelines for their use in the design of pavement rehabilitation.

The success of this project would be reflected in the adoption of guidelines and methods for AASHTO and in the number of DOTs that adopt some or all of the techniques for the evaluation of rehabilitation projects. Before-the-project and after-the-implementation-project surveys should reveal the usefulness of this research.

Currently, many rehabilitation design decisions are made on the basis of incomplete information which carries two dangers: 1) subsurface conditions that come to light during construction causing redesign, delays, and change orders and 2) subsurface conditions that are not caught during construction, which lead to early failure. While some of the equipment mentioned can be expensive and there are additional personnel costs in their deployment, the benefits of getting a better design far outweigh the costs.