The density of an asphalt pavement after construction is a key indicator of its durability and ability to withstand traffic demands in the coming years. Achieving desired and consistent pavement density can have tremendous impact on pavement life, with small differences having major cost implications for future maintenance, repair and reconstruction. Drilling and testing core samples remains a common method for testing density, but such spot checks are time intensive, damage the pavement and cannot accurately represent the density of the entire paved area. A promising alternative is the dielectric profiling system (DPS), sometimes referred to as a density profiling system, which uses noninvasive ground-penetrating technology at the pavement’s surface to measure and report the density of the area in real time, continuously and completely. However, while the science is sound, many questions stand as barriers to deployment of DPS in the field. To develop DPS into an effective and efficient technology that can be put into practice, Transportation Pooled Fund study TPF-5(443) was initiated in 2020, funded by lead organization Minnesota Department of Transportation (DOT), 13 additional state DOTs and FHWA. This pooled fund study undertook research and study in seven tasks areas: (1) software and hardware improvements; (2) development of AASHTO data collection and analysis specification; (3) precision and bias testing; (4) equipment and operator certification; (5) support communications; (6) training and technical assistance; and (7) promotion of DPS technology. Representatives from national and state transportation agencies, academia and industry provided study guidance and oversight over findings, as documented at https://www.dot.state.mn.us/materials/dps/, and together moved this technology forward by determining barriers to the implementation of DPS for field measurement and acceptance, as well as tools and paths to overcome these barriers.  Lab and field full-scale testing was expanded to include simulation work by the FHWA NDE lab at Turner Fairbanks that shows promise in defining optimal conditions and best use of DPS technology. Near the end of the pooled fund study, which is scheduled to come to a close in late 2024, participants in an informal poll unanimously agreed that a second phase of the study is needed  to completing the study’s mission with emphasis on assisting states in implementation. 

All states (whether they were members of the initial phase or not) are encouraged to join the 2nd phase of this pooled fund, as the workplan will be designed to build on the successes of the previous phase as well as the fresh perspectives of new agencies joining for phase II.

The objective of the ongoing pooled-fund project is to use DPS to improve density construction leading to longer lasting pavements.  In addition, the goal is to reduce the need for destructive methods such as coring in evaluating the in-place density to improve both safety and coverage of the evaluation process.  Phase II will include both research and implementation track activities.  The second phase of the pooled-fund project will continue to build upon and advance the progress made in Phase I by answering technical and practical questions related to DPS and developing tools and guidance for implementing DPS in the field as a best practice for density measurement.

Detailed Phase II scoping work was conducted with input and review from Phase I participants. A final work plan will be developed based on the priorities indicated by the pooled fund participants during a kickoff meeting and related scoping activities, as well as evolving needs and changes in the state of the technology and industry. However, based on the discussion among the current participants, it is anticipated that the work plan will consist of three tracks: research and development; implementation; and marketing and communication. The research and development track will address outstanding technical and engineering questions: (1) field, lab and simulation research of critical factors to develop best and worst use conditions for DPS; (2) evaluation of improved data collection methods; (3) benefit-cost analysis of DPS compared with other density measurements; (4) development of advanced analysis techniques; and (5) identification of uses of dielectric data without converting to density. A parallel implementation track will continue to address user needs and barriers in these areas: (6) development of training, demonstrations and pilot projects; (7) updating AASHTO specifications and ghost implementation protocols; (8) support of a national pilot project ghost implementations; and (10) development of a DPS certification center. Marketing and communication will include continued support through meetings, webinars, publication of findings and summaries, updates to the DPS website with detailed program content, technical training, implementation training, and technology promotion and marketing. Across all of these tracks and tasks areas, tentative specific subtasks have been scoped but remain open to further definition and revision.  An outline of the proposed tasks can be found here: DPS Workplan - Materials & Road Research - MnDOT (state.mn.us)

This project is expected to have a minimum participation of at least five agency members with a minimum annual commitment of $25,000 per agency. The study period will be set for four years.  A matching funds waiver to allow for 100% SP&R funding for this study has been requested.