Environmental Impacts on the Performance of Pavement Foundation Layers
Anticipated Project Start Date: July 1, 2019
Anticipated Project End Date: April 30, 2020
Seasonal freeze-thaw weakening and changes in saturation level from environmental fluctuations have a significant effect on pavement foundation performance. The seasonal freeze-thaw cycles cause extensive damage to the pavement from frost-related problems such as frost heave, frost boils, thaw weakening, rutting, and degradation of mechanical properties. Changes in saturation level of pavement foundation geomaterials during freeze-thaw cycles can influence the performance of pavement foundation layers significantly. It is crucial to monitor the changes in water content, temperature, and matric suction of base materials and subgrade soils to be able to predict the frost depth, freezing and thawing times and mechanical property changes.
This project has two main goals: (1) develop a model to predict the maximum/minimum frozen soil depths, freezing and thawing duration via use of standard climate data that includes precipitation, shortwave radiation, and air temperature and (2) develop a model to predict the performance of pavements that are subjected to severe freeze-thaw cycles.
During this phase (Phase I), the research team will extract the environmental data and pavement performance data (e.g. FWD, rutting) collected by MnROAD test facility over the years and determine whether it is necessary to build new test sections that is installed with finer environmental sensors to improve the reliability of a thermo-hydro-mechanic model to predict the pavement performance, freeze-thaw cycle numbers, freeze time and thaw time, and frost depth and be used for pavement analyses.
The research team will investigate several different software programs with capabilities for modeling heat flow and moisture transport. Modeling analyses will be conducted both in 1-D and 2-D to determine whether results are impacted significantly at different dimension conditions. Then, the research team will provide recommendation whether finer environmental sensor installation and monitoring is required considering sensor location, e.g., installation at the two edges, center and between edges and center of the roadway cross-section and different depths. For instance, sensors will be placed in every 6 inches in depth up to 10 ft. Thus, as a result, the lateral and vertical variations of these environmental data will be monitored and tied to the elastic modulus data.
The proposed study will help optimize the use of recycled materials and LSSB in pavement systems and lead to more consistent specifications between agencies. Other benefits the state will receive from the results and conclusions of this research include: (1) virgin material cost savings from the use of recycled materials; (2) longer pavement service life, resulting in reduced life cycle costs; and (3) conservation of natural resources resulting in reduced environmental impacts. The outcome of this research in the form of a pavement design specification could be immediately implemented by the department of transportations (DOTs) of states participating in National Road Research Alliance (NRRA).
The long-term benefits of the proposed project will be to improve the quality, longevity, and state of good repair of roadways, which constitute a vital component of the nations` infrastructure. The field monitoring data will produce a better understanding of the evolution of freezing and thawing soil zones beneath roadways. The computational models developed in this study will help DOTs advance towards predicting the depth and duration of soil freezing/thawing and stress resistance. As a result, maintenance costs associated with repairing traffic-related damage to thawing roads can be reduced.
With further research, the modeling analyses will determine whether more detailed Phase II study needs to be conducted. It is expected that with more detailed phase study in the future the computational models developed in this phase could be incorporated into the pavement Mechanistic Empirical Pavement Design Guide (MEPDG) for improved climate modeling and prediction of freeze-thaw related damage to ACC and PCC pavements.
The overall research methodology is proposed by a highly-qualified team with expertise in pavement systems and geotechnical engineering at Iowa State University (ISU) and the Geoengineering Consultant, LLC. The methodology primarily involves collecting field data and conducting modeling to predict frost depth, freeze/thaw periods and cycles, and pavement stresses under these conditions. Based on the results of this study it will be determined whether more detailed environmental sensor installation and monitoring is required to develop a more reliable model.
The proposed team has been working on MnDOT data for years and very familiar with the process. This phase of the project contains four tasks: (1) initial memorandum on expected research benefits and potential implementation steps, (2) collection of field data from MnDOT, (3) modeling, and (4) final report.
Task 1: Initial Memorandum on Expected Research Benefits and Potential Implementation Steps
Description: During the proposal phase and the development of the work plan, key benefits were selected to clearly define the benefits the state will receive from the results and conclusions of this research. This task will provide an initial assessment of research benefits, a proposed methodology, and potential implementation steps.
- Anticipated Start Date: July 1, 2019
- Scheduled Date to Submit Draft Deliverable: August 30, 2019
- Scheduled Date for Task Final Approval: October 30, 2019
- Duration: 4 months
- Deliverable: A memorandum providing initial estimates of expected research benefits, documentation of the methodology, and potential implementation steps.
Task 2: Field Data Collection
Description: Under this task, the research team will collect and analyze the falling weight deflectometer (FWD), pavement surface conditions, moisture content, temperature, and matric suction potential data. The degree of saturation level (moisture content) is the most influential parameter on the stiffness and strength of pavement performances. Therefore, it is very important to collect these parameters properly along with temperature data. Dr. Cetin and Dr. Edil have worked on the analyses of the similar data from the 2008 MnDOT project sites. The database of MnROAD will be scanned through in detail to extract any available and useful data to be used during modelling analyses. In addition, Dr. Cetin is currently leading a project “TPF5-(341) - Determining Pavement Design Criteria for Recycled Aggregate Base and Large Stone Subbase” funded by NRRA which also collects similar data. The data that has been collected through this project will also be used during modeling analyses. It is worth to note that Dr. Cetin has already developed an extraction and data analyses code written in MATLAB for the MnDOT 2008 road test sections and has analyzed the data. This code will be used to collect the field data to determine the number of freeze–thaw (F-T) cycles and the frost depth and be used for model calibration.
- Anticipated Start Date: July 1, 2019
- Scheduled Date to Submit Draft Deliverable: September 30, 2019
- Scheduled Date for Task Final Approval: November 30, 2019
- Duration: 5 months
- Deliverable: An interim report and webinar
Task 3: Modelling Analyses
Description: In this task, the pavement design and climate data will be utilized as input into the multi-physics modeling softwares. The model will be developed and run over a range of conditions, calibrated through adjustments to the model parameters (e.g. moisture, matric suction, temperature, elastic modulus), then evaluated through cross validation. The goal of this task will be to develop a forecasting model that will allow frost depth and timing, stiffness performance to be predicted based on input soil, pavement base layer, and weather data.
This task consists of two parts. First part includes the evaluation of software programs to determine which one would be the best option to model the complex thermo-hydro mechanics of the freezing and thawing pavement foundation layers in response to climatic inputs. The second part of the modeling is to calibrate the model to the measured data to develop forecasting tools. The research team is planning to try the COMSOL, SHAW, and PLAXIS softwares.
Using the measured data (e.g. moisture, temperature, matric suction, elastic modulus) as input, the project team will then begin developing and calibrating preliminary computational and theoretical models for predicting frost depths and freeze/thaw durations/cycles, and pavement performances. For greater practical implementation by other states, the forecasting accuracy of the computational models adopted will also be examined using only freely available above-ground weather data from the National Weather Service (e.g., temperature, precipitation, humidity, and wind speed) as inputs.
- Anticipated Start Date: September 1, 2019
- Scheduled Date to Submit Draft Deliverable: December 31, 2020
- Scheduled Date for Task Final Approval: February 28, 2020
- Duration: 6 months
- Deliverable: Presentation to the TAP and interim report
Task 4: Final Report
Description: During this task, the approved report will be processed by MnDOT’s contract editors. InTrans publication staff is very familiar with submitting final reports for MnDOT projects and they will ensure the report is in the correct format and meets all the requirements.
- Anticipated Start Date: January 1, 2020
- Scheduled Date to Submit Draft Deliverable: February 28, 2020
- Scheduled Date for Task Final Approval: April 30, 2020
- Duration: 4 months
- Deliverable: Final published report
Project Technical Advisory Committee (TAP) – email the TAP
Terry Beaudry (MN)
Raul Velasquez (MN)