The Asphalt Institute (AI) has a rich history of paving the way in engineering, research and education. In this second installment celebrating AI’s 90 years of contributions to the asphalt industry we take a closer look at more recent accomplishments, specifically training courses, programs and publications.
With the success of Full-Depth asphalt in the late 1960s, AI engineers began discussing the Full-Depth concept with engineers all over the U.S. Full-Depth asphalt lowered the stress on the subgrade and reduced the total pavement thickness. It could be built faster, easier and more economically than any other pavement type.
In the early 1970s, AI led the change from traditional penetration grading to a viscosity grading system. By the mid-70s, a national move to conserve energy and materials and to preserve the environment sparked a widespread interest in recycling. It was a practical and economical way of reconstructing old pavements.
For conservation and environmental reasons, city street and county road engineers across the U.S. began asking for information about asphalt emulsions. And the Clean Air Act of 1977 dramatically reduced the use of cutback asphalt. Consequently the Institute, together with the Federal Highway Administration (FHWA) and the Asphalt Emulsion Manufacturers Association (AEMA), developed the Basic Asphalt Emulsion Manual. Using this manual, AI engineers trained state and county road personnel in the proper use of emulsions through a series of regional workshops.
The focus of the paving industry shifted from new construction in the 1950s and 60s to rehabilitation in the 1970s and 80s. Because much of the Interstate system needed rehabilitation, state highway engineers turned to asphalt overlays because they were the least expensive and most reliable method of renewing pavements.
In the mid-1980s, the FHWA actively promoted their 3-R program—Resurfacing, Restoration and Rehabilitation. Highway engineers developed several ways to rehabilitate concrete with asphalt. California, along with Kentucky, Pennsylvania, Ohio and Virginia, found that cracking and seating the concrete slabs and overlaying them with asphalt was an effective method of rehabilitating concrete pavements.
Some states began to use rubblization with asphalt overlays to rehabilitate their concrete highways. Ohio and North Carolina analyzed the life-cycle cost of rubblizing and found it was the most economical method of rehabilitating concrete.
During the late 80s, state highway agencies recognized the ability of pavement management systems (PMS) to analyze pavement performance. AI’s Pavement Rating System for Low Volume Roads (IS-169) was used extensively by cities and counties to analyze the performance of their pavements.
The 1990s—Superpave and the National Asphalt Training Center
The most significant technological initiative for AI in the 1990s was the implementation of the National Asphalt Training Center (NATC). Embraced and promoted by AI members, AI saw the NATC as an effective way to develop and promote the Strategic Highway Research Program’s (SHRP) Superpave technology. Funded by FHWA, the AI Training Center functioned as the primary facility for agency and industry personnel for training in Superpave technology.
A major goal of SHRP research was to establish the relationship between fundamental chemical properties and pavement performance. The University of Texas at Austin developed a Materials Reference Library of selected asphalts and aggregates for use in the SHRP research program. Eight asphalts were used in the initial phase of the contract and 24 at a later time. Asphalts were selected based on crude oil source and the physiochemical properties of the crude oils and asphalt cements produced from them.
The Asphalt Selection Expert Task Group led the process of selecting the asphalts used in the Reference Library. The Group was composed of personnel from FHWA , Transportation Research Board (TRB), State Highway Departments and Asphalt Institute Members. The selection process specifically considered temperature susceptibility and aging. Temperature susceptibility was indicative of thermal cracking and permanent deformation (rutting).
PG Asphalt Binder Precertification
Precertification was a critical period in the life of the Asphalt Institute laboratory. The official name of supplier precertification was Performance-Graded Asphalt Binder Certification. Its purpose was to expedite the process by which a supplier could be approved by a state agency. The asphalt suppliers, mostly AI members, were concerned that certification tests by the states would take too long to complete. So AI members did their own certification, which was accepted by the states.
The AI member certification process minimized the disruption of PG binder shipments. It was accomplished by a system that evaluated quality control and specification compliance tests performed by the supplier. Standardization of procedures allowed an approved supplier the flexibility to use its existing facilities and limit shipping disruptions. Testing was done by an accredited laboratory.
In 2000 AI engaged in an important industry coalition charged with furthering the use and quality of hot mix asphalt pavements through research, technology transfer, engineering, education and innovation. The Asphalt Pavement Alliance is a partnership among AI, the National Asphalt Pavement Association and the State Asphalt Pavement Associations. The APA emphasizes the sustainability, life-cycle costs of asphalt as well as promoting the technology to produce quiet pavements. The alliance also sponsors the annual Asphalt Pavement Conference and the Perpetual Pavement awards. APA has awarded 59 Perpetual Pavement awards since 2001, celebrating asphalt pavements that are at least 35 years old and have never had a structural failure.
PPA Modification of Asphalt
The publication IS-220, Polyphosphoric Acid Modification of Asphalt, was developed by AI members through AI’s Technical Advisory Committee and the Affiliate Committee. This study concluded that the use of PPA, in the appropriate amount, improves the physical properties of asphalt paving grade binders. Used alone or in conjunction with a polymer, PPA can improve the high temperature PG grade, and with some asphalt sources, can improve the low temperature PG grade.
Safe Handling of Hot Asphalt
In 2003, the AI Health, Safety and Environment Committee produced the VA-26, Safe Handling of Hot Asphalt video/DVD and supplemental training workbook. The combination of the two provided excellent training tools and guidelines for anyone handling and transporting asphalt. The program describes loading precautions from the loading rack, details pre-trip inspections and the proper procedures for safe asphalt storage.
Bailey Method Seminars
The mission of educating industry professionals spawned two AI seminars covering the Bailey Method of gradation evaluation in 2004. The one-day “Introduction to the Bailey Method” course is designed for individuals with mix design or quality control experience wishing to learn the basic fundamentals of the method. The three-day “Achieving Volumetrics and HMA Compactability Course” covers the fundamentals but also the full potential of the principles to improve volumetric controls, aid in field compactability and gauge mix segregation potential.
Quantifying the Effects of PMA
Polymer-modified asphalt (PMA) has been used in the U.S. and Canada for many years to reduce distress and extend the service life of hot mix asphalt (HMA) pavements. Agencies have reported moderate to excellent performance from PMA mixes.
Because PMA is more expensive than traditional HMA, it is important that the effect of PMA on pavement performance be quantified as accurately as possible to compare the life cycle costs of both pavements. The AI Affiliate Committee recognized the need and requested that a study be made to quantify improved pavement performance when using PMA mixes. ER-215, Quantification of the Effects of Polymer-Modified Asphalt for Reducing Pavement Distress, published in 2005, accomplished that objective.
In 2007, AI’s Moisture Sensitivity Subcommittee produced the MS-24, Moisture Sensitivity Manual. The Subcommittee believed the manual was necessary because moisture sensitivity has become a nationwide problem. The most common form of moisture damage is adhesion failure between asphalt and aggregate, which is primarily the lack of a chemical bond. The addition of either a liquid antistrip or hydrated lime creates a chemical bond. Eighty-two percent of the states require some form of antistripping treatment.
The Asphalt Institute and the Asphalt Emulsion Manufacturers Association (AEMA) jointly updated MS-19, The Basic Asphalt Emulsion Manual in 2008. The primary purpose of revising the manual was to impart a basic understanding of asphalt emulsions to those who work with the product. It is intended to be useful in choosing the emulsions that best fits a project’s specific conditions. It is also helpful in evaluating pavement systems for construction and maintenance, and it serves as an aid in solving problems that may rise on projects where emulsions are used.
MS-25 and NBTC
AI’s MS-25, Asphalt Binder Testing: Technician’s Manual for Specification Testing of Asphalt Binders was introduced in 2008 to meet a growing national need for expanded binder training. Inspired by and in conjunction with the New England Transportation Technician Certification Program (NETTCP), AI also introduced the National Binder Technician Certification program in 2008. The program is helping reduce asphalt binder testing variability.
AI Director of Engineering Mark Buncher, Ph.D, P.E. authored the report Development of Guidelines for Rubblization along with Gary Fitts, Tom Scullion and Roy McQueen for the Airfield Asphalt Pavement Technology Program. The 2008 report provided specific details on all aspects of rubblization and documented the state-of-the-art technology for the process involving airfield pavements.
From 1919 through today, AI has transformed the education of agency personnel, industry engineers and paving professionals in the use of asphalt. As a result, the Asphalt Institute has long been regarded as the first and last word on asphalt here in the U.S. and around the world.
|Kendal Butler, Brian Clark and John Davis contributed to this story.|