Minnesota Department of Transportation

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NRRA Rigid Team

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MnROAD | NRRA | Structure & Teams | Rigid Team

Use of Early Loading to Increase Joint Deployment in COAs

Status: Active


Thin concrete overlays on asphalt (COA) are designed with small panels (typically 6 feet long) to reduce curling, warping and load related distresses. Recent performance observations in Minnesota have highlighted though that many of these closely spaced transverse contraction joints are not deploying. Lack of deployment can result in several concerning phenomenon, including wider joints spaced up to 60 feet apart, and a reduction in ride quality from joints deployed at an average spacing of 12 ft. The longer-term effects on performance of COAs due to these features is still being determined.

There are several features of COAs that create challenges when trying to deploy saw-cut joints. In order to deploy transverse joints, the concrete must be placed on a material that has sufficient friction to grab the concrete as it shrinks, but not so much friction that it restrains the frictional forces. To remove near surface distresses and/or lower the increase in grade associated with overlays, most COA projects involve removal of a portion of the asphalt using diamond grinding. Diamond grinding however results in a rough surface which the concrete bonds very well to. This bond provides structural benefits to the concrete overlay, but also significantly increases the frictional forces during the time of shrinkage. In addition, the increasing use of structural fibers in concrete overlays can add further restraint to joint deployment. The application of traffic loads eventually increases the number of deployed joints, but often not 100% of them. To fully meet the intended design of the overlay, all joints should deploy as early as possible.

Mechanisms to increase the number of early deployed joints is limited. Adjusting the saw-cut depth may encourage earlier deployment but might come at the expense of reducing the already small amount of aggregate interlock available within the joint faces of thin concrete overlays. The earlier application of traffic loads seems to be a more logical choice; this must however be balanced with limiting potential damage to the thin concrete panels. MnDOT has recently been working with contractors to explore whether the frequency of joint deployment in COAs can be increased using very early truck loading. These efforts have not been coordinated or consistent, leading to inconclusive results.

The objective of this NRRA research project is to replace existing COA cells at MnROAD with two new COA test sections that will explore the efficacy of early loading on increasing joint deployment under much more control conditions. In addition to two early loading periods, another variable was added in the form of two different joint saw-cut depths, in order to establish whether that might affect early joint deployment. Following construction and early loading, the new test cells will be monitored for joint deployment and overall performance over the first 3 years of life. During the same time period, additional COA projects throughout Minnesota (and other NRRA member states) will also be studied as they receive early loading intended to increase joint deployment.

Project tasks/status

Task 1: Literature review

In this task, the project team will perform a thorough search and detailed review of literature on the use of early loading to deploy transverse joints in thin concrete overlays on asphalt. The literature review will focus specifically on variation in timing of the early load application, as well as other features like saw-cut depths. This information will be compiled into a technical memorandum delivered to MnDOT, along with a technical presentation to TAP.

Task 2: Construction Activities

This task involves quantifying the deployment of transverse joint saw-cuts due to natural shrinkage of the concrete, as well as early application of truck axle loads intended to encourage additional deployment. This study will primarily utilize two new concrete overlays on asphalt (COA) test cells constructed at MnROAD in 2022. Periodic visual inspections and ultrasonic tomography will be used for detection. Data from inspections and sensors will be processed and entered into the MnROAD database. A technical report will be prepared to summarize task findings and submitted to the TAP, along with a summary presentation to the TAP.

  • Deliverable: See Task 3 deliverable.
  • Scheduled Date for Task Final Approval: December 22, 2023

Task 3: 1st Year Performance Update

Under this task, the first-year performance data collected by MnROAD staff on the two COA test sections will be gathered and summarized. The following data are expected to be reported on: joint deployment, FWD data, seasonal ride quality measurements, distress survey information, environmental response and load test data from embedded strain sensors, MIRA and fault meter measurements, joint opening measurements (automated and manually collected), curling and warping measurements, and other testing data on extracted cores. Based on the findings, any recommendations for data collection adjustments (i.e., type, frequency) will be communicated to the TAP. A 1st year performance summary report will be provided to the TAP for review and comment. A summary of key findings will be presented to the TAP and/or at NRRA Research Pays Off webinar sessions.

Task 4: 2nd Year Performance Update

The second-year performance data collected by MnROAD staff on the two COA test sections will be gathered and summarized. Efforts will mirror that described in Task 3. Comparisons and findings will include data from the 1st and 2nd years of performance monitoring.

  • Deliverable: Technical Report and Presentation to TAP and/or NRRA Research Pays Off Webinar
  • Date due: January 31, 2025

Task 5: 3rd Year Performance Update

The third-year performance data collected by MnROAD staff on the two COA test sections will be gathered and summarized. Efforts will mirror that described in Task 4. Comparisons and findings will include data from the 1st, 2nd, and 3rd years of performance monitoring.

  • Deliverable: Technical Report and Presentation to TAP and/or NRRA Research Pays Off Webinar
  • Date due: January 31, 2026

Task 6: Determination of impact of early loading on increasing joint deployment in thin concrete overlays on asphalt

The primary goal of this task is to determine whether early loading, along with other variables like joint saw-cut depth or time of loading, has an effect of increasing transverse joint deployment in thin concrete overlays on asphalt. Available data MnROAD and other test sites will be analyzed and summarized in a technical report.

  • Deliverable: Technical Report and Presentation to TAP
  • Date due: January 31, 2026

Task 7: Final Technical Review and Revisions of Final Report, and Tech Brief

The research team will prepare a draft final research report and technical brief document (to aid in implementation) that provides a project overview, data, findings, and conclusions. At this time, the report is envisioned to include the following sections:

  • Chapter 1. Introduction, Purpose, and Scope.
  • Chapter 2. Construction Activities.
  • Chapter 3. Performance Comparison and Findings
  • Chapter 4. Impact of Early Loading of COA on Joint Deployment
  • Chapter 5. Findings and Conclusions.
  • Appendices: Literature Review Summary, Project Data Summaries, etc.

The draft final report and technical brief document will be provided to the TAP 2 months in advance of completing this task. After the draft report is submitted, a TAP meeting will be scheduled to review the contents of the report.

  • Deliverables: A revised document that is technically complete and approved by the TL for publication, Presentation to TAP, and/or NRRA Research Pays Off Webinar
  • Date due: March 31, 2026

Task 8: Editorial Review and Publication of Final Report and Tech Brief

During this task, the PI will work directly with MnDOT’s contract editors to address any editorial comments and finalize the document or product in a timely manner. The contract editors will ensure the product meets MnDOT’s publication standards and accessibility guidelines (WCAG-compliant).

  • Deliverables: Final publishable document(s) that meets MnDOT’s publication guidelines and standards
  • Scheduled End Date: May 30, 2026

Related materials

Project team

Email the Project Team
Principal Investigator: Tom Burnham, Senior Road Research Engineer, MnDOT, tom.burnham@state.mn.us
Co-PI: Michael Wallace, Concrete Research Scientist, MnDOT, Michael.Wallace@state.mn.us
Technical Liaison: Joseph Podolsky, MnDOT, Joseph.Podolsky@state.mn.us
Technical Advisory Panel (TAP): Contact us to join this TAP

  • Manik Barman, University of Minnesota - Duluth
  • Robert Golish, Minnesota DOT
  • Tirupan Mandal, Wisconsin DOT
  • Joseph Podolsky, Minnesota DOT (TL)
  • Hamed Sadati, CalTrans
  • Xijun Shi, Texas State University
  • James Wilde, Texas State University