Three software programs are among the resources that are having some profound changes on concrete pavement design. Along with other resources currently being developed, these programs hold great promise for optimizing pavement design and returning greater value to all stakeholders, including the traveling and taxpaying public.
Able to predict
Following more than a decade of development, the Mechanistic-Empirical Pavement Design Guide (M-E PDG) is, at this writing, moving closer to full approval by the American Association of State Highway & Transportation Officials (AASHTO), an important step in implementation among state agencies.
Developed as a comprehensive highway design resource, M-E PDG is based on inputs that relate directly to loading, climate, support, placement conditions and mix design, as well as a host of real-world conditions that can impact pavement performance.
The guide also includes defined modes of failure including cracking, faulting and the International Roughness Index (IRI) for concrete pavements, and rutting, fatigue cracking, thermal cracking, IRI and others for asphalt pavements. The common denominator for failure is once again based on ride quality as determined by IRI.
This ability to predict specific distresses may ultimately result in a better comparison of equivalent pavement sections. A key to realistic comparisons will be for state agencies to calibrate the guide using the best available local data and set comparable design periods and failure criteria. Without local calibration and comparable failure criteria, an agency will find the results inconsistent with their experience since the default data was set as generalized criteria.
The newly approved version of the M-E PDG is now available online at the Transportation Research Board’s website (www.trb.org/mepdg).
From inception to the present day, ACPA has been involved in the planning, review and now delivery or implementation of the M-E PDG.
Word on the street
ACPA’s StreetPave software program is designed to optimize concrete pavement design for highways, as well as municipal and county roads.
By analyzing the cost of a pavement under specific traffic loads and over a set amount of time, it allows designers and engineers to base decisions on long-term pavement performance.
StreetPave is specifically valuable for those involved in the design of municipal streets and roadways because the analysis tools include updated information on current material costs and additional considerations, such as curbing.
For highway design, the software tool also provides an accurate look at how a pavement will hold up under specific truck volume.
StreetPave is available in both a full-scale CD-ROM software version and an online version. The full version of StreetPave includes a number of additional features that allow designers to optimize concrete pavement thicknesses for municipal, county and state highways and roadways.
It includes an asphalt cross-section design process (based on the Asphalt Institute method) to create an equivalent asphalt design for the load-carrying capacity requirement. A “Life Cycle Cost Analysis” module allows detailed cost-benefit analysis. StreetPave is compatible with Windows 95, 98, NT, 2000 and XP. For more information, visit the ACPA bookstore at www.pavement.com/bookstore. (ACPA members also may access the bookstore by logging into the members-only portion of the website.)
Already own the full version of StreetPave? ACPA also is offering a free patch to upgrade the original version of StreetPave to Version 1.2. Visit ACPA’s website (www.pavement.com/StreetPaveV12Updates.doc) for a Word document containing details about the patch. To download and install the file, go to www.pavement.com/Concrete_Pavement/Technical/Downloads/Software.asp.
The free, online version of StreetPave includes many of the same features as the full original version of the software for a quick, cursory look at pavement design. The online version is available at www.pavement.com/StreetPave/Default.aspx.
Air-born solutions
ACPA’s AirPave software, originally released in 2000, is valuable design software for engineers looking to automate the process of determining necessary thickness for concrete pavement runways.
The latest version includes features that allow engineers to customize concrete pavement airfields to accommodate a specific fleet of aircraft. The new version also lets users save their work for future pavement determinations.
This eliminates both the number of calculations and some subjective factors that historically have been part of designing airfield pavements.
These additions are incorporated into the basic steps in running the software. To run AirPave, users first customize concrete airport pavements to support a specific fleet of different aircraft using ACPA’s updated AirPave software. With that, users then:
1. Input specific characteristics about the pavement to be constructed, including a thickness value;
2. Choose from a list of more than 25 popular aircraft in more than 59 configurations, including the A300, B777 and military aircraft (users also can customize configurations for any vehicle that will travel on the pavement, such as forklifts, cranes, straddle carriers, tracked vehicles, trucks and non-standard aircraft); and
3. Click for a report that calculates fatigue life and stress ratios for pavements bearing loads.
The new version of AirPave is in the final review process and should be released shortly.
