Solutions to Mitigate Dowel/Tie-Bar Propagated Cracking – Phase 1
Project End Date: June 30, 2022
The goal of this project is to identify the cause(s) and contributing factors of concrete pavement longitudinal and delamination cracking caused by dowel and/or tie-bars. This will be accomplished by reviewing existing literature and developing case studies of projects in NRRA member states exhibiting dowel and/or tie-bar related distresses. Based on the case studies, Contractor will be responsible for proposing analytical and/or laboratory experiments that will enable the development of solutions that mitigate longitudinal and/or delamination cracking caused by dowel bar and/or tie-bar stresses.
Task 1: Literature review
Conduct a comprehensive literature review. Focus effort on Contractor’s transportation libraries, the personal files of project team members, and other Contractor staff, national and international studies, as well as the libraries, databases, and publication directories of the many transportation organizations located in the U.S. and throughout the world. Focus the literature search on reviewing and assessing past dowel and tie bar propagated cracking incidents, other restraint cracking incidents, possible causes of cracking, mechanism of cracking, and mitigation methods. Evaluate the influence of various triggers and variants, and document solutions to control cracking. Include a review of analytical methods and tools used to model cracking, and specifically dowel and tie bar cracking in concrete pavements. Collect past cracking experiences from various U.S. States and Canadian Provinces. Contact various State Department of Transportations (DOTs), Canadian Ministries of Transportation, and industry associations; and document individual experiences and resolutions. Meet with the Technical Advisory Panel (TAP) to discuss findings.
- Deliverables: Task 1 memo (pdf), 8/16/2021
Interim memo documenting the findings of the literature review as it relates to dowel and tie bar propagated cracking, and analytical methods used to model such cracking. In addition, the interim memo will address past dowel and tie bar cracking experiences from various agencies including those in Canada.
- Expected: March 30, 2021
Task 2: Case studies
Based on the information collected in Task 1, work with the Technical Advisory Panel (TAP) to identify a minimum of six case studies in NRRA States for further evaluation. The purpose of the case study is to identify a variety of situations under which dowel and/or tie bar cracking has been observed. If necessary, utilize contacts at DOTs and industry associations to supplement candidates for case studies. Provide the following criteria to the agency contacts as they recommend the candidates:
- Available information: The candidate project will have sufficient information available. At a minimum, the information will include the following:
- Project information including location, design, traffic, climate, and other site characteristics.
- Construction records including paving stations/mileposts and dates, ambient weather conditions during construction, dowel placement, concrete mixture design, quality assurance data, documented construction issues, etc.
- Pavement performance data in terms of cracking and other distresses. The performance data will include not only the current condition but also a history of pavement deterioration since its construction.
- Pavement age: The candidate project will be young enough to still have good quality design and construction data but old enough to show the performance information as it has changed over time.
- Availability of companion sections: Identify (if possible) potential situations where portions of a project exhibited tie bar or dowel bar cracking, while other portions of the same project did not exhibit such cracking. The goal is to isolate causes of cracking and identify potential ways to mitigate dowel and tie bar propagated cracking.
Starting with a moderately long list (12-15+) of candidate projects, screen the candidate projects based on data availability and project uniqueness. After the initial screening of candidate projects for the case study evaluation, gather detailed information for each of the projects including the following:
- Location, age, traffic, site conditions, etc.
- Historical weather data during construction.
- Pavement design and concrete mixture design reports.
- Construction documents and drawings.
- Construction quality control and acceptance records.
- Access to the project management and construction administrator to interview.
- Pavement management (performance) data.
Compile the information gathered from each project into a 4-5 page project information summary to send to the agency project contact and TAP for review, making any changes/corrections, etc. before the field investigation. Estimate the duration of lane closures required to conduct each field investigation (for example, if dowel alignment data is to be collected or if coring is to be performed). Initiate coordination with State or County personnel in planning for the field investigation.
- Deliverables: Provide a minimum of six draft case study reports to be sent to the agency project contact and TAP for review, and for planning the field investigations.
- Expected: April 30, 2021
Task 3: Field investigations
Upon approval by the TAP, conduct the field investigations. The purpose of the field investigation is to identify and capture potential factors that contribute to dowel or tie bar propagated cracking by inspecting pavements that exhibited such cracking incidents and also similar adjacent sections with lower occurrence of such cracking incidents. Survey a minimum of six sites located in various NRRA member states where past dowel or tie bar cracking has occurred. As discussed below, evaluate companion sites that are relatively similar (e.g. part of the same construction project) but do not exhibit dowel or tie bar cracking. This approach is designed to provide an effective sampling matrix. After gathering and reviewing all of the available information, work with the NRRA State or County personnel to coordinate traffic control and visit the selected project sites for a field investigation. Include visual inspection of the roadway, and evaluation of joint condition and distresses. Collect field cores or material samples and perform dowel alignment testing, as and where necessary. Evaluate if any Falling Weight Deflectometer (FWD) data collection on this project is needed on a project-by-project basis to identify the extent of curling and warping of the concrete slabs.
Visual inspection of roadway conditions:
- Assess the overall pavement condition(s) impacting the occurrence of cracking for the particular project.
- Prior to the setup of traffic control, begin the field assessment by driving the project in both directions to get familiarized with the site and to identify any locations requiring closer observation.
- After the traffic control has been setup, revisit the identified areas for a detailed evaluation in accordance with the Distress Identification Manual produced for the Long-term Pavement Performance Program (Miller and Bellinger, 2013) and the Guide for Forensic Investigations of Highway Pavements (Rada et. al., 2013).
- Treat each of the six sites as a special case study.
- After each visit to the field project, summarize the key information and prepare a draft case study report.
- Include detailed information and lessons learned along with the photos gathered from the site visit.
Evaluation of joint conditions: Utilize Magnetic Imaging Tomography (MIT) scan to evaluate dowel bar alignment where it is suspected as causing cracking. Dowel bar misalignments can potentially lock up the joints and prevent them from opening and closing freely, which may result in cracking near the joints.
Evaluation of Drainage System: Investigate and evaluate the drainage system conditions including subsurface drainage, pavement subdrains outlets, pipes, and culverts. High moisture (relative humidity and precipitation) in pavement structure has the potential to increase volumetric expansion in the concrete pavement.
- Deliverables: Provide fully updated case study reports (drafts developed in Task 2) incorporating key aspects of the field data collection to be sent to State and TAP for review and feedback.
- Expected: July 31, 2021
Task 4: Report
Submit a written document summarizing the results and key findings from the field investigation including the potential mechanism of dowel and/or tie bar cracking, potential solutions to mitigate dowel and/or tie bar cracking, and the potential factors attributed to dowel and/or tie bar cracking in the NRRA states.
- Deliverables: Prepare a report summarizing the findings from the literature search and field investigations.
- Expected: December 31, 2021
Task 5: Presentation
Present to the TAP and the NRRA Rigid Team members, the results and key findings from the field investigation including the potential mechanism of dowel and/or tie bar cracking, potential solutions to mitigate dowel and/or tie bar cracking, and potential factors attributed to dowel and/or tie bar cracking in the NRRA States.
- Deliverables: Prepare a presentation summarizing the findings from the literature search and field investigations, and present findings to the TAP and NRRA Rigid Team members.
- Expected: December 31, 2021
Task 6: Analytical and laboratory experiments
Develop analytical and laboratory experiments to investigate mitigation strategies for longitudinal and/or delamination cracking caused by dowel bar and/or tie-bar stresses. Develop a detailed work plan for analytical and laboratory testing to be conducted in Phase 2 of this project. Review conclusions from Tasks 1-5 and identify key parameters that contribute to dowel or tie-bar propagated cracking. As discussed in previous sections, a large number of potential variables are responsible for damage with potential for significant interaction between these parameters. Utilize Finite Element Analysis Tools (FEA) to evaluate the thermomechanical stresses that cause cracking.Utilize nonlinear FEA tools to perform a number of deterministic analyses of this potentially large parameter space.Utilize computational experimental designs to perform efficient parameter variations and conduct sensitivity studies to identify the main effects driving the damage. This approach is useful in evaluating the potentially significant interaction between many parameters that drive damage. Based on the FEA results to identify key mitigation approaches, validate a subset of analyses by performing laboratory experiments that provide the best potential for improvements. With approaches identified and validated with experiments, analyze the field applications with the validated FEA model. Using conclusions drawn from literature review and field investigations in the previous tasks, select key parameters to study in this analyses. In addition to a large set of parameters studied, uncertainties exist in various model input parameters and in the concrete pavement environment. It is important to understand and quantify the effect of these uncertainties on the predicted outcome to develop bounds on the potential variability of the predicted result. Develop a fractional factorial experimental design to perform critical modeling parameter screenings that drive the concrete cracking and to bound the variability in the amount of concrete damage. Fractional factorial designs are two-level designs that are executed at high and low values for each variable. These designs require fewer than the usual 2k+1 runs needed for a one at a time plus center point design. Using fractional factorial experimental design, optimize the number of simulations required to study the various combinations of parameters and identify the parameters driving the concrete cracking. The Finite Element Modeling (FEM) tool selected will need to explicitly model concrete damage well, so utilize the LS-DYNA FE code (LS-DYNA 2015) for these analyses. LS-DYNA is a nonlinear explicit FE code for the dynamic analysis of structures and has widespread acceptance in the engineering community. LS-DYNA is commercially available and is based on the public domain DYNA3D FE code developed at the Lawrence Livermore National Laboratory. LS-DYNA is also well-suited for a transient analysis of the stresses developed in the reinforced concrete due to heat of hydration, thermal expansion, wheel loading, etc. Utilize the results of the FEA study to identify design options for reducing longitudinal and/or delamination cracking caused by dowel bar and/or tie-bar stresses. Identify select cases from the FE analyses for laboratory experiments, and utilize the laboratory experiments to validate the FEA models. Using the validated models, model field applications based on the design options chosen from this study. Utilize the results from the field investigation and preliminary analytical analysis to establish the laboratory experimental setup and the testing matrix. Validate the models used in this study and confirm the potential cracking in the concrete that can occur. Develop a test article consisting of a single dowel bar in a concrete slab (with a width the same as the spacing between dowels). Supported to best approximate to the substrate and void beneath the slab. Utilize results from this study to guide the experimental design. Apply the loads derived from this study on dowel bar 1 with a load frame to the test article. Utilize a finite element model of this test setup, using the models developed here, for comparison and validation. Testing matrix will include:
- Concrete mixtures (high cement vs. low cement, high flyash vs. low flyash, various Coefficient of Thermal Expansion [CTE] mixtures, etc.)
- Slab thicknesses (thin slab vs. thick slab)
- Curing conditions (wind, temperature, etc.)
- Dowel and tie bar types (size, materials, etc.)
- Simulated curling/warping by changing support conditions.
- Deliverables: Develop a memo document to propose analytical and/or lavatory experiments for Phase 2.
- Expected: February 28, 2022
Task 7: Final report
Submit a final report summarizing the entire research results including results and key findings from the field investigation, potential solutions, and potential factors attributed to dowel and/or tie bar cracking in the NRRA States. The final report will also include Phase Two analytical and laboratory testing work plan.
- Deliverables: Prepare a report summarizing the entire research effort and a presentation summarizing the findings from the literature search and field investigations.
- Expected: February 28, 2022 (Draft); April 30, 2022 (Final)
Task 8: Presentation
Present report and findings at the NRRA Annual Meeting or during an NRRA Research Pays Off webinar.
- Deliverables: Present report and findings at the NRRA Annual Meeting or during an NRRA Research Pays Off webinar.
- Expected: April 30, 2022
Principal Investigator: Shreenath Rao, Applied Research Associates, Inc.
Technical Liaison: Peter Kemp, Wisconsin DOT
Project Technical Advisory Panel (TAP) – Email the TAP
Contact us to join this TAP
- Tom Burnham, Minnesota DOT
- Ashish Gandhi, Owens Corning
- Peter Kemp, Wisconsin DOT (TL)
- Leo Mahserelli, Caltrans - California DOT
- Maria Masten, Minnesota DOT
- Kevin McMullen, Wisconsin Concrete Pavement Association
- Jim Parry, Wisconsin DOT
- Larry Scofield, American Concrete Pavement Association
- Brett Trautman, Missouri DOT