Tag Archives: pavement design

Upgrading MnPave-Rigid Design Software

MnDOT has upgraded its software for concrete pavement design. MnPAVE-Rigid 2.0 is now easier to use and allows designers to select from more options for aggregate base types and thicknesses, and incorporate specific traffic values.

“In the original software, we only allowed one aggregate base thickness and one aggregate type. MnPAVE-Rigid 2.0 allows two base thicknesses and three base types,” said Tim Andersen, Pavement Design Engineer, MnDOT Office of Materials and Road Research.

What Was the Need?

MnDOT developed its own pavement design software, MnPAVE-Rigid, in 2014 that incorporated the methodology of the American Association of State Highway and Transportation Officials (AASHTO) Mechanistic–Empirical Pavement Design Guide (MEPDG). Minnesota’s pavement designers use MnPAVE to apply AASHTO’s most sophisticated design principles for both rigid and flexible pavement, focusing on mechanical properties of the pavement and prevention of early cracking and other distress.

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MnDOT engineers use sophisticated and complex M–E pavement design methods from MnPAVE-Rigid 2.0 software to design durable, high-performing concrete pavements.

AASHTO’s mechanistic–empirical (M–E) design methods entail hundreds of inputs, each a mechanical parameter, a measure of site-specific characteristics or a design goal. To simplify the input selection process, AASHTO’s M–E design software offers various input levels to reduce the data gathering and input burden. The most basic level uses default values for most of the inputs based on national averages, but still requires dozens of inputs for the number of pavement layers, traffic expectations, climate and other features.

MnPAVE-Rigid for concrete pavement design reduced that number of inputs to nine, operating like a module of AASHTO’s M–E software. MnPAVE-Rigid inputs work with a set of default values for jointed plain concrete selected by the MnDOT Office of Materials and Road Research in 2014, as described in the MnPAVE-Rigid 1.0 report.

“Many states ignored the challenge of adopting AASHTO M–E or they bought an AASHTO
software license. MnDOT used its accumulated knowledge of AASHTO M–E and Minnesota conditions to build MnPAVE-Rigid, and so can account for its M–E design results firsthand,” said Derek Tompkins, Principal Civil Engineer, American Engineering Testing, Inc.

Since implementing MnPAVE-Rigid 1.0, MnDOT has gathered feedback from users about their experience with the software. In the current project, MnDOT wanted to address this feedback, and expand and improve the original software by exploring additional options with some of the default parameters for concrete pavements.

What Was Our Goal?

The goal of this project was to update MnPAVE-Rigid 1.0 by expanding the range of inputs for traffic, subgrade type, base type and thickness, and to make the user interface more accessible.

What Did We Implement?

MnPAVE-Rigid 2.0 allows users to enter 11 inputs, including inputs related to specific traffic levels and aggregate base types; calculate the new design thickness; and print a project report that summarizes the inputs and the recommended thickness. The upgraded software is more user-friendly, and MnDOT can maintain or make future upgrades to the source code.

How Did We Do It?

Researchers met with the Technical Advisory Panel and reviewed the list of software improvements requested by pavement designers and the MnDOT Office of Materials and Road Research.

Because every change to an input affects a large number of default input variables, investigators ran over 21,000 simulations to analyze the impact of changes made to inputs for base type, base thickness, subgrade type and traffic level. The research team also modified the traffic input calculator to allow designers to enter traffic values from MnDOT’s weigh-in-motion and traffic counting data. The calculator runs input traffic data in software simulations and assigns the input an appropriate axle value for design.

MnPAVE-Rigid 1.0 ran designs based on Class 5 aggregate base over a subgrade like clay loam. Other aggregate types were added to simulations to determine how the software responds to these changes. Investigation also explored the addition of subgrade material options in design simulations.

The code developer modified elements of the advanced inputs tab and PDF report generation features to improve performance for software users, and rebuilt the software in JavaScript 2.0 code, including an installer for use with Windows software.

What Was the Impact?

MnPAVE-Rigid 2.0 is more user-friendly. Its tabs better match designer needs, and the software offers a design report PDF file for export. Instead of selecting from limited options for traffic volumes (default, normal and heavy), users can now input traffic data that the software will categorize. Designers can input Class 5 aggregate, Class 5Q (a higher quality aggregate with fewer fines) and open graded aggregate (no fines). Users can also choose 4-inch or 12-inch aggregate base thicknesses. An additional subgrade option was not included, as simulations indicated a sand subgrade input did not discernibly impact structural thickness outputs.

The AASHTO M–E software is expensive, and agencies that use it have to work closely with consultants to receive training and to explore or modify the code. MnDOT owns and manages the source code for MnPAVE-Rigid 2.0, can keep it secure, and can continue to change and upgrade it internally for Windows and Linux platforms.

What’s Next?

MnDOT designers around the state are reviewing the software, but it is essentially already in use. After full review, the Office of Materials and Road Research will post a link to the program on its website. Presentations about the software upgrades will be made at meetings for materials and soils engineers through the fall of 2018.

Still underway is an effort to further incorporate recycled material properties into MnPAVE Flexible, the design software for asphalt pavement.

This Implementation Summary pertains to Report 2018-17, “MnPAVE-Rigid 2.0,” published May 2018.

New research to explore innovative solutions to aging pavement infrastructure

New solutions are urgently needed to address Minnesota’s aging pavement infrastructure since current materials and technologies can’t keep up with the rate of deterioration and limited funding.  MnDOT recently entered into a contract with the University of Minnesota to further explore new materials and technologies – including taconite and Graphite Nanoplatelets (GNP) – that could offer cost-effective solutions for longer-lasting pavement.

Background

The university has investigated the use of taconite aggregates for more than a decade (see ongoing and completed research), and started investigating GNP-reinforced asphalt materials more than three years ago (see recently completed research). Both materials present very unique properties that can be used to better build and maintain asphalt pavements.

This research project will focus on two applications with significant potential in the pavement area:

  • Early detection and repair of cracking by developing a novel asphalt material in which GNP materials, taconite concentrate, and conventional asphalt binders are combined for damage sensing and healing. The material damage will be assessed by measuring the electrical resistance, while the damage healing will be achieved by applying microwave to the material.
  • Thermal enhancement of tack coat bonding between asphalt overlay lifts, using GNP and taconite concentrate and microwave heating. Poor bonding can result in many different pavement distresses that decrease the pavement structural strength and life, ranging from top-down cracking, potholes and fatigue failure.

Improving pavement durability

The latest data shows that 15 percent of roads in Minnesota are in poor condition, at a cost to each motorist $480 per year. Low-temperature cracking is one of the main causes of pavement failure in Minnesota. Studies have shown that early detection of damage and cracking and timely repair is essential for extending the lifespan of the pavements.

Each dollar spent in the early-stage of pavement life could eliminate or delay $6 to $10 in future rehabilitation or reconstruction costs.

A series of recent studies funded by the National Cooperative Highway Research Program (NCHRP) and MnDOT showed that the GNP-modified asphalt binders and mixtures exhibit a significant improvement in both mechanical and compaction properties. The combination of the previous research and the proposed research will fully explore the properties of GNP-taconite modified asphalt binders and mixtures as a multi-functional pavement material, which will address various needs of MNDOT, including high fracture resistance, efficient compaction process, and cost-effective pavement preservation operations. By addressing these needs, the result of this research will lead to an innovative and efficient means to improve the long-term durability and resilience of asphalt pavements in Minnesota.

 Project scope

The two-year research project aims to explore the damage sensing and healing capability of asphalt binders and mixtures modified by GNP and taconite concentrates. The essential idea is to combine GNP and taconite concentrates with asphalt binders to make the final asphalt products electrical conductive. By measuring the change of electrical resistance, researchers will be able to determine the damage extent. When the damage extent reaches a certain level, the University will apply microwave to the pavement to generate heat, which will heal the cracks through viscous flow of warm asphalt binder. In addition, the thermal bonding capabilities of a novel tack coat material also modified with GNP and taconite concentrate will be investigated. The research will consist of four parts:

  1. Electrical conductivity tests on GNP-taconite modified asphalt binders and mixtures
  2. Modeling of relationship between electrical resistance and damage extent
  3. Investigation of self-healing capability through microwave
  4. Investigation of a microwave-based tack coat system to enhance thermal bonding in asphalt paving

Watch for new developments on this project here.  Other Minnesota pavement research can be found at MnDOT.gov/research.

 

Videos trace progress in traffic operations, pavement design

Last month, CTS debuted two videos about the many contributions U of M researchers have made—and are still making—in traffic operations and pavement design.

The videos are one of the ways CTS is marking 30 years of transportation innovation. Our goal is to show how research progresses over time—from curiosity to discovery to innovation. The videos also show how U of M research meets the practical needs of Minnesotans in the Twin Cities metro and throughout the state.

The first video focuses on improving traffic operations, a research focus since our earliest days. Professor Emeritus Panos Michalopoulos invented Autoscope® technology to help transportation agencies capture video images of traffic and analyze the information, enabling better traffic management. Autoscope was commercialized in 1991, and the technology has been incorporated into products sold and used worldwide.

Current traffic operations research builds on this strong foundation. For example, the U’s Minnesota Traffic Observatory, directed by John Hourdos, develops data collection tools such as the Beholder camera system. The system is deployed on high-rise rooftops overlooking a stretch of I-94 in Minneapolis—an area with the highest crash frequency in Minnesota—to help the Minnesota Department of Transportation reduce congestion and improve safety.

The second video showcases U of M research on pavement design. Developing pavements that can stand up to Minnesota’s harsh climate is a continuing priority for researchers, whose work has led to new methods, tools, and specifications to extend pavement life. The video also looks at how research teams are pushing the envelope with use of materials such as taconite waste and graphene nano-platelets for pavement applications.

 

New Tool Measures Impact of Heavy Trucks

A new tool developed by the Local Road Research Board helps cities and counties assess how much increased heavy vehicle traffic affects local roads.

Researchers created an analysis method and corresponding spreadsheet tool that city and county engineers can use to calculate the impact of heavy vehicles on asphalt roads beyond what was planned in the original pavement design.

The information will help agencies optimize services, such as garbage collection, for the least amount of damage. It will also help agencies better plan roads in new developments, as well as redesign existing roads that are nearing the end of their lives.

Lack of Data

Heavy trucks cause local roads to deteriorate more quickly than passenger vehicles, but it is challenging to quantify the impacts, especially for areas where traffic was not forecast at the time a road was designed.

Many local engineers in Minnesota have requested information about the impact of heavy vehicles in light of new construction, commercial distribution facilities and hauling routes. This information is needed to assist in local road planning and maintenance.

Two Methods

In a newly completed study, investigators developed two methods for calculating heavy vehicle impact:

  • Calculate the additional bituminous material (and associated costs) that would have been required to construct the pavement had the heavy truck traffic been predicted when the pavement was designed.
  • Calculate the portion of a pavement’s design life, measured in equivalent single-axle loads (ESALs), consumed by unanticipated vehicles.

“Before this project, there wasn’t an easy way for an engineer to determine how much a specific truck was going to decrease the life of a road,” said  Deb Heiser, Engineering Director, City of St. Louis Park.

Whereas previous research has calculated the impact of extremely heavy vehicles over the short-term (typically the course of a construction project), this project calculates the impact of long-term increases in traffic from vehicles that are heavy, but still mostly within normal legal weight limits.

The tool can be used for a single street segment or an entire road network. Users can also compare current situations with proposed ones to evaluate the impact of potential changes in heavy traffic levels.

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