By Dave Johnson, P.E.
The third edition of the Asphalt Institute’s “MS 22 – Construction of Quality Asphalt Pavements” is now available. For 35 years, this book has served as the Asphalt Institute’s comprehensive manual on asphalt pavement construction. It has been widely seen as one of the finest resources on the topic.
The first edition of MS-22 came out in 1983. It was the best resource on the construction of asphalt pavements available to the paving community at that time. It served the industry well until it was updated as a second edition following the development of Superpave in 1998. Not surprisingly, the primary changes found in the second edition reflected the Superpave mix design process and the Performance Grading system for asphalt binder grading. This too was a great resource to the asphalt world which it has served for a generation.
The goal of this third edition remains to provide a concise and practical resource of essential technical information and best practices for constructing cost-effective, long-lasting asphalt pavements. Contractor personnel, user agencies, specifiers, consultants and others involved in asphalt paving will benefit from this new edition – particularly inspectors, project engineers, paving crews/foremen/superintendents, plant operators and testing technicians.
“We set out to not only update the existing manual but combine the knowledge of our team of excellent engineers into one resource for paving professionals,” said Asphalt Institute Director of Engineering Dr. Mark Buncher.
This 2020 edition was updated to incorporate the latest technology, equipment, methods and standards.
Readers will find a more thorough discussion of various topics compared to previous editions. There is now a dedicated chapter on transportation/delivery of mix, as well as a new chapter on properly preparing the surface and underlying pavement. Segregation is addressed in each of the respective chapters where it can occur. An emphasis is placed on the importance of balanced paving operations in all four construction phases: production, transportation, paving and compaction.
Examples of new technologies covered in this edition include specialty rollers, intelligent compaction, performance testing, plant equipment and various quality assurance approaches.
It’s in there
The manual has ten chapters covering the entire process before, during and after actual construction. As a comprehensive manual, it addresses all significant aspects of asphalt pavement construction. Some of the highlights of the first chapter include an introduction to asphalt and its many uses; the way in which asphalt mixtures are classified and defined and it introduces the need to balance the four phases of the construction process for asphalt pavements.
Chapter 2 is devoted to project documentation and personnel roles and responsibilities for both the owner and the contractor’s teams. Pre-paving meetings and job site safety are also addressed in the chapter.
Information on the two main materials that are used to build an asphalt pavement, the asphalt binder and aggregate are found in Chapter 3. Regarding the binder, significant discussion is made of a binder’s unique characteristics at both high and low temperatures and how they change with time as the material ages. Further discussion is offered on specification systems and how to select and test a binder for a project.
Chapter 3 also includes information on aggregate sources and production, as well as an extensive discussion of desirable aggregate properties. The final topic is an important look at recycled or repurposed materials – reclaimed asphalt product (RAP) and recycled asphalt shingles (RAS).
With this background on the material properties of a pavement’s building blocks, chapter 4 dives into the mix design process for asphalt. Some of the topics therein include the objectives of a mix design and the properties that should be considered. Volumetric properties, which have been the basis of mix designs for years, are given a fair bit of time. They are also the basis for the measurement of quality by facility owners, so control of these properties is very important.
The reader can then find a presentation of the basic process that happens during a mix design. Key elements of the process, such as the meaning and determination of different specific gravities for the aggregates, or the importance of mixture conditioning are covered. The increasingly common use of performance testing is also explored, along with the balanced mix design concept. Finally, chapter 4 addresses the need to tweak the mix design during construction and how to best do that.
Asphalt plants are dealt with extensively in chapter 5. The mixture production process plays a key role in the concept of a balanced paving operation. The process must manufacture a steady and consistent supply of on-specification asphalt mixture that meets the demand of the paving operation. This is accomplished through the proper handling, storage and blending of raw materials:
• Stockpile an adequate supply of tested and approved raw materials
• Use uniform and continuous (minimal stops) plant operations
• Manufacture and temporarily store the required amount of finished mixture
• Use proper techniques to prevent physical and thermal segregation
These are all vital to a successful production operation and are covered in detail in this chapter.
The transportation (hauling or trucking) and delivery process play key roles in the concept of a balanced paving operation and they are explored in chapter 6. The hauling operation must provide a steady and consistent flow of asphalt mixture from the plant to the paver. It is accomplished by ensuring:
• Timely and proper loading of the haul vehicles at the plant
• Adequate number of haul vehicles to support continuous paver speed (with minimal stops) throughout production
• Consistent use of proper techniques for unloading haul vehicles to provide uniform flow of asphalt materials into the paver
• Delivering mixture that meets temperature and segregation requirements
Attention to each of these vital components of a successful haul operation are covered in detail in this chapter.
The entire life of a pavement is affected by the quality of the materials upon which it is built. Hoping to encourage the practice of paving on worthy materials, chapter 7 is devoted to preparation for paving and tack coats. All of the surfaces that are commonly paved whether new, existing or a rehabilitated surface are discussed. Special attention is given to tack or bond coats as layer bonding is so vital to future performance.
Placement of the mixture (the laydown process) is also important to a balanced paving operation. Chapter 8 deals with the laydown operation. It must provide a steady and consistent flow of asphalt mixture from the hauling unit (truck) in order to build a uniform width and depth mat behind the paver to the proper line and grade. Achievement of this is done by ensuring:
• Properly sized paver to adequately handle the required production
• Consistent and uniform flow of mixture through the paver
• Continual use of best practices to set up and operate the paver
• Placement of the mat with adequate temperature for compaction and without physical segregation
Compaction of the mixture is the last of the four elements of the construction process that needs to be balanced for a smooth consistent paving operation. Chapter 9 is focused on compaction.
The compaction operation must provide consistent compactive effort to the newly placed asphalt mat so that target density is achieved by ensuring:
• Compaction is completed in the optimum temperature range based on the mix type, binder grade and environmental conditions
• An adequate number and type of rollers are used so that the compaction operation keeps up with the paver without exceeding each individual roller’s recommended speed
• Establishment of the roller patterns specific to that project based on construction of a density test strip at the beginning of the project
• Best practices for roller speed, roller patterns during mat and joint compaction are used continually and consistently throughout the project
The investment that is made to construct a traffic or parking surface with asphalt is significant. Therefore, it behooves the owner to have a means of verifying that they are getting what they are paying for. This is done with a quality assurance (QA) program which is addressed in the final chapter of this new manual, chapter 10.
Eight subcategories are fully expounded upon in this chapter. Information on how to set up a QA plan; what, how and where to sample; what tests to consider performing on the samples; and the most common acceptance philosophies are some of the many topics found in chapter 10.
The goal is top-quality pavements
MS-22 recognizes that successfully creating a quality asphalt pavement cannot simply be accomplished with good paving and compaction operations but must also consist of proper pavement design, materials selection, mix design, plant production and quality assurance. Using best practices in each of these phases helps ensure the resulting asphalt pavements are built to last.
“Our Asphalt Institute engineers spread the word about quality asphalt pavements across North America and even the world,” said AI President Pete Grass. “This extensive manual encapsulates those many lessons and pointers along with the decades of experience from our team.”
While this manual covers the core construction topics in detail, secondary topics are covered in less detail but still provide an adequate understanding as they pertain to the construction process. Asphalt Institute and other industry references are often listed that provide further in-depth coverage of these topics. This will make it easy for readers to explore these topics in greater detail as they see fit.
This manual furthermore serves as a key reference to many of the Asphalt Institute’s educational courses covering construction. Most prominently, this manual will function as a textbook for our updated MS-22 seminars entitled “Constructing Quality Asphalt Pavements.” These one-day seminars continue a long-standing tradition of topnotch industry instruction by Asphalt Institute engineers.
We believe this third edition of MS-22 will serve the industry well for many years as the most thorough go-to reference on asphalt pavement construction.
Johnson is an Asphalt Institute Senior Regional Engineer based in Montana and one of the authors of MS-22.