Innovative Asphalt Pavement Technology: Paving the Way for the World’s Roadways

The centerline mileage of roadways in the United States is about 4.1 million, an increase of 12% in the last 50 years (Figure 1). During this same time period vehicle miles of travel (VMT) have increased by over 240% (Figure 1). About 71% of the roadway miles are located in rural areas and about 29% located in urban areas of the country (1).

Various federal agencies own and operate about 3.4% of the highway mileage. State highway agencies or departments of transportation own and operate about 18.9% of the network. The remaining highway network is owned and operated mostly by local agencies: counties 43.9% and cities 32.4%. Other owners account for 1.4%.

About two-thirds of the roadway mileage is paved (2.75 million miles) whereas about one-third remains unpaved (1.36 million miles). The percentage of paved surfaced roadways has increased from about 50% to 67% over the last 50 years. Asphalt binders are used on about 94% of the paved surface mileage whereas portland cement concrete accounts for about 6% of all paved road mileage surfaces. Thus, over 2.5 million miles of roadways are surfaced with asphalt bound paving materials.

Highway expenditures in 2015 were $235 billion with about $77 billion used for debt retirement, bond interest, and law enforcement (1). The remaining $158 billion was utilized to manage, plan, design, construct, rehabilitate, and maintain the highway infrastructure. It is difficult to determine the percentages of these highway expenditures that are utilized for design, construction, and rehabilitation and maintenance of pavements. Estimates range from about 30% to 60% of the total budgets depending on the jurisdiction. A more detailed analysis from one state department of transportation indicated about 35% of the total is being utilized on pavements. Annual expenditure in the range of $50 billion to $60 billion per year for pavement design, construction, and rehabilitation and maintenance is a reasonable estimate.

Asphalt pavement binders are utilized in pavement construction for subbase, base course, and surface layers. The largest consumption of asphalt binders in paving applications is for hot mix asphalt (HMA) and warm mix asphalt (WMA). These materials are produced, transported, and placed at elevated temperatures. WMA is typically produced at temperatures 20°F to 40°F below the temperatures of HMA (about 300°F). WMA makes up 40% of the production of asphalt paving mixtures at elevated temperatures. Foaming techniques are utilized to produce 65% of WMA mixtures (2). This document will utilize the terminology of HMA to imply both HMA and WMA. The industry terminology for HMA and WMA continues to change.

Other uses of asphalt binders include applications that do not directly add structural, load carrying ability to the pavement. These applications include relatively thin surfacing materials such as chip seals, microsurfaces, slurry seals, fog seals, prime coats, and a variety of maintenance mixtures. It should be noted that some states utilize chip and slurry type seals extensively whereas other state highway administrations do not use these surfacing materials. Base and subbase stabilization with asphalt is utilized by some public agencies. Asphalt cements, emulsified asphalts, and cutback asphalts are all utilized as binders in roadway construction. Asphalt cement is the binder utilized in HMA. The term asphalt binder will be utilized in this paper to designate asphalt cement, emulsified asphalt, and cutback asphalt. Cutback asphalt use is limited by environmental and health and safety concerns associated with the hydrocarbon diluents used in their manufacture.

HMA production in 2017 was about 375 million tons (2). As indicated above, 40% of this production utilizes warm mix additives including both foam and chemical additives. State highway agencies and other public agencies including cities and counties use about two-thirds of the total production of HMA. Private work (commercial and residential) accounts for the remaining one-third of the production. State highway agencies utilize about 45% of HMA production (2).

Research, development, or implementation of new technology for asphalt bound pavements that results in an incremental increase in pavement life or reduction in first cost for materials or pavement structural sections can result in substantial cost savings. For example, HMA production in the United States has historically ranged between about 350 million and 500 million tons on an annual basis. At a price of $70 to $75 per ton in-place (cost of materials and construction) for this paving material, the annual expenditures are of the order of $25 billion to $35 billion. If the life of this paving material can be increased about 1 year, an annual saving of about $2.5 billion will result. Research, development, and implementation efforts have successfully introduced the use of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) that reduce the initial cost of the HMA by about $5 to $8 per ton. This has provided an estimated annual saving to the citizens of the United States in excess of $2 billion.

As discussed above, one of the major driving forces for change in the asphalt paving industry has been economics. Small changes in prices of materials, equipment, processes, or increases in the life of pavements result in billions of dollars of savings. However, economics has not always been the major driving force for change. Other factors include safety, environmental awareness, energy availability, asphalt binder availability, and limited funding for highways, among others. Some of these driving forces will be briefly discussed.

As discussed previously, the 1973 Oil Embargo caused several technical and economic dislocations leading to relatively rapid development of technology. Accompanying the technology development was a general reduction in available funding for highway construction and rehabilitation and maintenance. The condition of the nation’s highways deteriorated. The primary performance problems recognized in the early 1980s were rutting, water sensitivity of asphalt mixtures, transverse cracking, and aging. These problems were recognized by the leaders of the Federal Highway Administration, American Association of State Highway and Transportation Officials, state department of transportation officials, and industry and their associations.

Key dates and activities associated with this national research and development effort are shown in Table 1. Initial work on research needs was started in 1983 with the formation of the Strategic Transportation Research Study (STRS) Committee. A variety of activities followed resulting in the Strategic Highway Research Report (SHRP) that defined the research program in 1986 (5). A $50-million research and development program was developed with key research directed towards the following: asphalt binders, asphalt mixtures, pavement performance, and performance-based specifications.

Research results were available in the early 1990s and included the performance-graded (PG) asphalt binder specification, a new method for asphalt mixture laboratory compaction, as well as new test methods for mixture design. The effort associated with the implementation of SHRP was extensive and continues today. Some of the lessons learned from this effort include the following:

Pavement thickness design concepts were developed based on soil mechanics principles in the 1930s. Two- and three-layer elastic solutions were available to predict deflections and stress and strains in pavement layers by the late 1950s. The first linear elastic multilayered pavement analysis computer program was developed in the mid 1960s by Chevron Asphalt. Shell Oil developed a multilayer elastic computer program shortly after. Layered elastic programs have been utilized as a research tool since the 1960s and have been incorporated into mechanistic empirical pavement design procedures used by some state highway agencies (Figure 4).

In the late 1970s and early 1980s linear viscoelastic and nonlinear viscoelastic methods were introduced. Finite element approaches to pavement design were also developed during this period. The FHWA research during the 1970s was the most widely known viscoelastic-based method during this period. Technology originating from solid rocket propellants research was utilized to help develop these approaches. These more advanced mechanistic methods have improved the engineer’s ability to predict permanent deformation or rutting in pavements and cracking resulting from repeated traffic and from the environment and subgrade conditions.

Layered elastic and viscoelastic and other solid mechanics approaches allow engineers to calculate stresses, strains, and deflections in pavements under a variety of loading and environmental conditions. Fracture mechanics has been utilized to predict various forms of cracking based on calculated stresses and strains.

Layered elastic and finite element models to calculate stress, strain, deflection, and permanent deformation require the pavement materials to be characterized. Characterization of pavement materials to provide the parameters for input into these computer programs is relatively complex. For example, unstabilized subgrade, subbase, and base material properties are stress and moisture content dependent. Asphalt bound materials are loading time and temperature dependent. Asphalt bound materials also change with time (aging) and with the presence of moisture. The aging phenomenon in asphalt pavements is somewhat similar to a rubber band aging and cracking. Proper characterization of pavement materials is time consuming and has been a major issue associated with implementation of these more advanced methods of pavement design.

The theory available to calculate stress, strain, and deformation is far more accurate than the ability to characterize materials. In addition, the correlation of these calculated parameters and their associated materials inputs with field performance needs to be further developed to determine robust failure criteria. This has been a difficult task and a challenge.

The perpetual pavement concept developed in the 2000s is based on limiting the stresses and strains in pavement layers. The use of engineering mechanics to predict these stresses and strains is an important part of the development of this concept. Commonly accepted failure criteria for pavement rutting, based on maximum vertical compressive strain on the subgrade, and for pavement fatigue cracking, based on maximum horizontal tensile strains in the asphalt bound layers, are utilized to design perpetual pavement. Theoretically, an extremely large number of traffic loads can utilize the pavement without the occurrence of rutting or fatigue cracking caused by very small increments of damage. The impact of environmental loads, loss of friction, and aging of the pavement materials is addressed by removing and replacing a thin layer of asphalt surface mixture every 10 to 20 years.

Asphalt binders are important from an economic point of view as well as being a major contributor to determining the performance of an asphalt pavement. Asphalt binders are complex materials of which the mechanical properties are difficult to define and the chemical properties are extremely complex. A chemical engineer with a major oil company indicated that the study of asphalt chemistry will remain difficult as the material contains millions of millions of individual molecules in very complex structures.

Asphalt binder technology has moved from the “chew” test in the early 1900s to determine asphalt binder consistency to advanced rheology techniques used by the polymer industry. Key properties of asphalt binders include the health and safety aspects of the material as well as consistency over a range of temperatures, loading rates and durabilities. Various types of rheological, mechanical, or physical tests are primarily used to characterize the viscoelastic properties of asphalt binders. A chemical test is used to determine the materials classification as “asphalt.” Asphalt binders are liquids at elevated construction temperatures and brittle solids at temperatures associated with in-service pavements in the winter.

Figure 5 illustrates the changes in the asphalt binder specifications that have occurred over the last almost 100 years. The needle penetration test was utilized to describe the consistency or stiffness of asphalt binders until about 1962. The PG system was developed in the Strategic Highway Research Program (SHRP) (5) during the late 1980s and early 1990s and is used in the United States and other countries.

Asphalt binders are viscoelastic materials and change physical properties with rate of loading and temperature. The penetration-based asphalt binder specification defines stiffness or consistency at a temperature of 77°F at a single loading rate. Properties were defined on the asphalt cement as refined and sold (original properties) as well as after conditioning (short-term) that simulated the amount of hardening or aging of the asphalt after mixing with the aggregate and placing as a pavement (construction operation).

The viscosity-based asphalt binder specification defined stiffness at temperatures of 77°F, 140°F, and 275°F. The viscosity was also determined at 140°F after laboratory aging (short-term) that represented the construction operation. Two different viscosity specifications evolved. The first specification was based on viscosity properties of the original asphalt binder whereas the second system, used primarily on the west coast of the United States, was based on the laboratory aged properties.

The PG system developed by SHRP defined the consistency or stiffness of the original asphalt binder at about 140°F and 275°F. Consistency was also determined at approximately 140°F on the laboratory aged asphalt binder that simulates construction hardening (short-term aging). Asphalt binder samples subject to long-term laboratory aging that represents the aging after about 5 to 7 years of service in a pavement were characterized at low and intermediate temperatures in the region of about 0°F and 77°F respectively.

Today’s research programs continue the evolution of the specification in terms of enhanced rheological property determination and environmental conditioning over a range of temperature and aging conditions that more accurately simulate the temperatures and aging conditions experienced by asphalt binder when used in asphalt pavement. The temperature range from about 0°F to 140°F represents the pavement temperatures experienced in asphalt pavement as utilized on pavements on roadways. The 275°F temperature represents a construction temperature associated with mixing the binder with aggregate in a plant and placing and compacting the mixture on the roadway. The SHRP-developed PG specification system for asphalt binders is a significant advancement in the technology, although quality relationships between asphalt binder properties and pavement performance are elusive.

Asphalt binder manufacturing practices have fundamentally not changed over the years. However, fewer asphalt binders are produced directly during the refining process today. These are typically called “straight run” asphalt: that is, refined to the specification grade at the refinery. Today a significant number of asphalt binders are blends of refined asphalt binders and any number of materials including those commonly available at refineries (flux oils and gas oils) as well as re-refined engine oil bottoms (waste transportation vehicle lubricating oil residue after processing), polyphosphoric acid, polymers, crumb rubber, and other softening and hardening materials. This blending is more likely to be performed in “terminals” rather than in large crude oil refineries.

The materials combinations identified previously are used to economically adjust low temperature and high temperature properties of asphalt binders to meet the PG specification as well as to improve the overall performance (in some instances). One of the most widely used groups of additives is polymers. Natural rubbers were utilized on a limited basis in the 1950s and styrene-butadiene random copolymers were utilized regionally in the 1960s for chip seals and for some asphalt mixtures produced at elevated temperatures. Styrene-butadiene-styrene (SBS) polymers introduced in the late 1970s and early 1980s are in relatively widespread use in many areas of the world. Additives that improve the water sensitivity of the asphalt binder and mixture include amine and diamine chemicals that promote attraction between asphalt binders and aggregates. Additives that alter the age hardening of asphalt binders (antioxidants) are needed.

Asphalt mixtures contain both asphalt binders and graded aggregates with or without other additives and modifiers. These mixtures are designed and constructed to minimize permanent deformation in the pavement (rutting), cracking caused by repeated loads (fatigue), cracking caused by changes in temperatures (thermal cracking), cracking caused by subgrade and base course volume changes, and cracking from existing pavements (reflection cracking). Asphalt mixtures harden with age in service and are sensitive to the presence of moisture or water.

Asphalt mixture properties change dramatically with test temperature and rate of loading. Thus, materials should ideally be characterized over a temperature range and loading rate that simulates the asphalt mixture in service. Test temperatures should range from approximately −20°F to 185°F. Loading rates experienced in the field range from static (creep type behavior) to 0.01-s load duration for high speed traffic. The ability of test load equipment and instrumentation to operate within this range is questionable. Thus, time–temperature superposition principles are often used and “master curves” are prepared from test data for asphalt mixtures as well as asphalt binders.

Recycling or reuse of existing pavement materials for pavement rehabilitation, reconstruction, and maintenance has been employed extensively for over 70 years. The various forms of pavement recycling are shown in Figure 7. The most common form of recycling is hot central plant recycling, with nearly 80 million tons of RAP used on an annual basis. All forms of pavement recycling became popular in the mid 1970s because of the increase in crude oil prices and the concern for the availability of binders for road construction purposes. Significant national research and implementation efforts advanced by the state departments of transportation and the Federal Highway Administration resulted in recycling technology development and deployment. As a result, substantial savings in pavement construction, rehabilitation, and maintenance have resulted from recycling asphalt pavement materials.

The use of pavement preventive maintenance materials dates back almost 100 years, but the use of fog seals, chip seals, slurry seals, and microsurfaces became more widespread as preventive maintenance tools in the 1980s because of Federal Highway Administration leadership. One state department of transportation currently spends over $300 million for chip seal annually. Slurry seals were introduced for roadway maintenance operations in the 1950s and have experienced mixed results. Rebranding of an improved slurry seal product in the 1980s resulted in the more widespread use of microsurfaces. This slurry product utilizes polymers, improved asphalt emulsions, and chemical accelerators to shorten the cure time of the product.

Optimization of the type and timing of rehabilitation and maintenance operations has saved significant amounts of money associated with providing safe and efficient transportation on the nation’s highways. Maintenance management and pavement management systems, first developed in the 1960s, have become increasing more sophisticated and can provide forecasts of funding needs through optimization techniques. Quality management systems have been developed since the 1970s and are in widespread use today. These systems govern the sampling, testing, and inspection of pavement construction.

The early maintenance management systems provided methods to identify and track expenditures for various maintenance operations on a roadway segment. Maintenance methods were defined in terms of equipment, personnel, and materials needs, as well as costs and productivity rates. These systems are used to establish work programs for maintenance crews.

The early pavement management systems were based largely on visual condition surveys of pavement surfaces that defined the type, extent, and severity of distress. Pavement management systems were developed for both network- and project-level decision makers starting in the early 1970s. Decision trees provided a link between pavement distress and rehabilitation and maintenance needs. Pavement performance deterioration curves were utilized together with optimization programs to determine financial needs to rehabilitate and maintain a roadway network over prescribed time periods. Most state departments of transportation utilize asset management programs to help direct highway expenditures for rehabilitation and maintenance on an annual basis.

The Federal Highway Administration has recently required the development of state Transportation Asset Management Programs (TAMP). Typical data collection efforts for these systems include bridge condition surveys and pavement condition surveys. Tools used for pavement condition surveys include visual condition surveys performed by human raters, condition surveys performed by video and transcribed into pavement condition, ride quality determination, pavement deflection to evaluate pavement load carrying capability, and friction measurements.

Quality management programs are central to achieving long lasting quality asphalt bound mixtures in pavement structures. Significant advances in quality management were made at the AASHO Road Test and some states used these principles to implement advanced quality control specifications based on statistics for both sampling and analysis of test results. West Virginia was a leading state in this effort in the 1960s.

Other states developed quality management systems based on statistical principles in the 1980s and 1990s. Many of these specifications utilized quality control and quality assurance types of specifications that assigned the responsibility for mixture design and some testing used for payment purposes (quality control) to the contractor. Some of these efforts accompanied the implementation of the SHRP research products.

The quest to develop or identify rapid test methods for quality control and quality assurance has been undertaken by the asphalt paving industry several times. Two national efforts to develop tests have been relatively ineffective. Rapid test method development remain a high priority need of the industry.

Test methods to measure the quality of paving mixtures need to measure parameters that are related to pavement performance. Specification tests need to be performance related or performance based.

The establishment of mathematical relationships or models among pavement material properties, layer thickness, traffic loads, and pavement performance are fundamental to the establishment of pavement thickness design and mixture design methods. Several full-scale test roads have been constructed over the years in the United States to establish these relationships. The test roads include the Road Test One placed in Maryland in the early 1950s to study portland cement concrete pavements, the Western Association of State Highway Officials (WASHO) test road constructed in Idaho in the early 1950s, the AASHO Road Test constructed and operated in the late 1950s and early 1960s for both asphalt and portland cement bound pavements in Illinois, MnRoad constructed in Minnesota in the early 1990s for both portland cement concrete and asphalt bound pavements, WesTrack constructed in Nevada in the early 1990s for asphalt bound pavements and the National Center for Asphalt Technology (NCAT) Test Track constructed in Alabama in the 2000s for asphalt bound pavements. MnRoad and the NCAT Test Track remain in service today. The test roads identified were tested under controlled traffic conditions with standard trucks operating at highway speeds. Other test roads in the United States and throughout the world have been placed on in-service highways without controlled traffic.

Road Test One, the WASHO Road Test, the AASHO Road Test, and MnRoad had major elements of their design and operations aimed at establishing relationships between pavement layer thickness and pavement performance. WesTrack, the NCAT Test Track, and MnRoad were and are being operated to establish relationships between mixture properties and pavement performance.

Other forms of accelerated pavement testing have been used throughout the world. Large-scale equipment has been developed to traffic small pavement test sections placed under field construction conditions. This equipment has been utilized in several countries including France, Spain, China, Japan, and the United States. The Heavy Vehicle Simulator (HVS) and the Accelerated Load Facility (ALF) are two examples of this type of equipment. Typical tires and wheel loads are applied under relatively slow traffic loading conditions. The loading devices can be located outside with or without environmental control capability or indoors.

Small-scale accelerated load equipment has also been developed for field and bench-top laboratory environments. These devices include the Hamburg wheel tracking device, the APA and the model mobile load simulator (MMLS 3).

During the 1970s a significant improvement in construction equipment associated with pavement construction, rehabilitation, preservation, and maintenance occurred. The Clean Air Act of 1970 stimulated the use of bag house and wet washer systems on HMA plants to improve air quality. The bag house is now the primary tool used to meet air quality standards in the developed countries.

Drum mix plants for HMA production were introduced in 1972 by Boeing in the state of Washington. Drum mix plants were used at low temperatures for the production of emulsion asphalt mixtures before this date. Initial production with drum mix plants occurred at somewhat reduced temperatures and with relatively high moisture contents. The development of drum mix plants by most major manufacturers involved the development of not only the concept of heating, drying, and mixing in one drum but also the inclusion of large quantities of RAP. Drum mix plants are “continuous” plants that do not stop production from batch to batch.

Drum mix plants are used today to produce relatively large quantities of HMA at elevated temperatures. Over half of all HMA plant are drum mix plants as compared with “batch plants.” Batch plants remain in use today primarily in urban areas where several different mixture types may need to be produced in a relatively short period of time.

To take advantage of the high production of drum mix plants, mixture storage silos were developed and attached to these plants. These storage silos allowed mixture to be produced at high production rates, stored, and loaded into trucks at a different rate.

One of the most useful items of equipment for pavement rehabilitation and recycling is the cold milling machine. The first cold milling machine was developed in 1974 and demonstrated to a Federal Highway Administration Expert Task Group meeting on recycling in Las Vegas. This equipment allowed for the economic removal of asphalt mixtures from the roadway and quickly became a “must have” tool for roadway rehabilitation.

The 1970s witnessed a significant development in equipment for both cold in-place and hot in-place recycling equipment. Improved pulverization equipment, portable crushing, and mixing equipment was developed during this period for CIR. Improved heating, mixing, laydown, and air quality control equipment was developed for hot in-place recycling during the 1970s and early 1980s.

Vibratory compactors were developed in the late 1970s and became commonly used for asphalt paving in the 1980s. These compactors or rollers allowed for more efficient compaction of asphalt paving mixtures. In addition, the roller widths became greater, which contributed to improved efficiency of the compaction operation.

The materials transfer device was developed in 1989 and affected the market in the 1990s. These devices allow for storage of the asphalt mixture (about 25 tons) at the laydown site, remixing, which reduces aggregate segregation and promotes temperature uniformity, as well nonstop movement of the paving machine, which improves smoothness of the riding surface.

The PG asphalt binder specification developed during the SHRP research program and the improvements made primarily through activities of the Federal Highway Administration Asphalt Binder Expert Task Group and its related research significantly improved specifications as compared with the penetration and viscosity-based specifications. Asphalt binder properties are determined over a wider temperature range and under both short-term and long-term aging conditions.

Continued technology development is needed to improve the characterization of polymer modified binders, determine the presence of various additives and modifiers, and improve the ability of test methods to predict short-term and long-term age hardening of asphalt binders in service in a variety of climates and mixtures. Chemical characterization of asphalt binders remains elusive and may not be possible because of their complex chemical nature. Research continues under NCHRP Project 9-60 as well as other federal and state funded projects.

Manufacture of asphalt binders will continue to change. Economics will continue to drive refiners and terminal operators to use a variety of materials and techniques to manufacture the asphalt binder. Although the asphalt binders produced will meet the existing specification, they may not have the properties that will perform under a variety of field production and exposure conditions.

Materials are needed to modify the aged asphalt binders contained in RAP and RAS. Both physical and chemical properties of the aged binders need to be modified by these materials.

Nanotechnology shows some promise to help solve asphalt binders’ challenges including aging and water sensitivity. New materials that alter the loading rate sensitivity of binders and the fracture properties of asphalt binders and the asphalt binder–aggregate interface are needed. Bio-based additives to binders are also being evaluated as rejuvenators.

Most asphalt mixtures designed today do not utilize a fundamental materials property test. Compacted air voids and controls on the rheological properties of the asphalt binders and physical properties of the aggregates are the primary mixture design controls. The gyratory compactor developed in the SHRP program is utilized as the primary sample fabrication tool today. The number of gyrations needed to simulate various traffic levels in different climates is not well defined.

Laboratory wheel track, rutting tests, and various forms of cracking resistance tests are sometimes used by public agencies for mixture design. Asphalt mixture water sensitivity tests are commonly used today.

Improved fundamental property tests are needed for asphalt mixtures. These tests should be performance related and include parameters that will control rutting and cracking (fatigue, low temperature, volume change, and reflection) under various moisture and aging exposure conditions. Sample preparation for these tests is key. As discussed previously, the mixture property tests should be suitable for the following: mixture design, pavement thickness design, and quality assurance.

Economical asphalt bound materials are needed to convert unsurfaced roadways to surfaced roadways and to provide a “hard” surface for low traffic volume roadways. Most of the miles of roadway in the United States are under the jurisdiction of local governments and their needs should be addressed.

Hot central plant recycling has become common practice in almost all states. Cold in-place and hot in-place recycling is utilized by some but not all states. Significant improvements have been made in recycling since the 1970s.

Improved asphalt binder modifiers are needed that will allow for recycling higher percentages of RAP and RAS in hot central plant operations. The improved modifier needs to resist age hardening in service and alter the chemical properties of the aged binders in the recycled material.

Cold in-place and cold central plant recycling equipment improvements have been significant over the last few decades. Research is underway and will need to continue to develop improved mixture design, structural design parameters, water sensitivity, and methods for curing and conditioning laboratory prepared samples to duplicate field curing conditions.

Hot in-place recycling techniques are utilized in some areas of North America, Japan, and Europe. Heat transfer physics limits these operations to generally treating about 2 in. or less of the old pavement. Improvements in heating technology, air quality control, and field performance studies will help develop the industry.

Pavement management systems, maintenance management systems, and quality assurance systems are all key to providing improved asphalt bound pavements. Pavement and maintenance management systems are mature and useful to those involved in scheduling maintenance operations in the short-term and tracking the condition of a public agency’s pavements. The use of the information contained in these systems by decision makers and planners for allocating financial resources at the annual, 4-year, and 10-year budgeting horizons needs improvement. Integration of these “big data” systems with construction, materials, and other public agency data systems is needed.

Rapid pavement evaluation equipment capable of operating at highway speeds and collecting continuous data needs further refinements. Advances in devices that use electromagnetic waves to determine pavement thickness, condition, surface texture, and drainage continue (ground penetrating radar and LiDAR for example).

Rapid quality control and quality assurance test methods are needed. The industry has largely been unsuccessful in developing meaningful, rapid test methods that can be utilized for equipment production process control and construction quality control. Hand-held instruments that evaluate and classify RAP and provide recommendations for the type and quantity of rejuvenator would be particularly useful.

Significant improvement in construction equipment has been made over the last several decades as discussed previously. Key equipment changes include the drum mix asphalt mixture production plant, air quality control equipment, cold milling machine, vibratory roller, and material transfer device.

The operational principles of the paving machine have remained unchanged for over 70 years. Asphalt mixture production batch plants have remained relatively unchanged for over 70 years as well.

Improvements in plants and equipment are constantly being undertaken by industry. Asphalt mixture plant production automation, intelligent compaction, automated machine guidance, GPS-based profile milling and laydown of pavement layers, e-ticketing, and information technology integrations of plant and field records for quality assurance purposes are examples of a few advancements that are underway.

Automated process control and quality control testing equipment that will sample and test materials rapidly will improve the quality of construction. Automated aggregate sampling and gradation testing equipment is an example of needed equipment that has been developed but has been difficult to deploy in the industry. Additional developmental efforts are needed in this and other equipment.

Accelerated construction techniques need to be developed. Construction is highly visible to the public, it affects the safety of the construction workforce and the driving public, and it affects the economy in which the construction project sits. The goal of accelerated construction is to reduce construction project time by as much as 70%. This is a large effort involving a workforce skilled in several disciplines including contracting methods, traffic management, work zone safety, materials, construction operations, economics, and construction equipment. The European development of “pavement on a roll” is an advanced example of some of the techniques that can be developed.

A significant number of construction projects are let each year to widening existing multilane and two-lane highways. New construction equipment and techniques are needed to remove and replace materials at an accelerated rate. Materials removal and replacement operations are conducted in the median areas as well as the outside edges of pavements.

Most state departments of transportation have reduced workforce numbers and have lost experience to retirements during the last decade. Developing the next generation workforce is necessary. Improved methods to transfer technology to the next generation are needed. Leadership is available to make this never-ending transition.

Small improvements in pavement performance of asphalt pavements will result in substantial dollar savings to citizens. Although small individual projects mostly performed at universities provide value, large, reasonably focused projects are needed to make significant contributions. Developing one test that may or may not be related to performance at a university is not the answer to improving the industry in a significant way. Relating measured test parameters to performance is a key to improving quality and life of pavements. Large projects involving accelerated field testing, and long-term pavement performance monitoring projects that are integrated with the research will be required. The SHRP Long-Term Pavement Performance (LTPP) project is an example of this type of effort in the United States. Pavement performance studies have been a key part of the asphalt pavement research effort in many areas of the world including Canada, Europe, China, South Korea, Brazil, Australia, and South Africa, to mention a few countries. These projects should be, in part, directed to provide for a resilient and hardened pavement infrastructure.

Local government needs should be recognized in research. Local governments also need to provide financial support. Research and development efforts led by industry have produced significant improvements in pavements. Typically, industry led technology research and implementation efforts are deployed without a reasonably complete understanding of the benefits and disbenefits. Public supported research is often needed to “refine” the product or process.

Public supported research is often slow to reach the market or enter the implementation stage. Understanding how to best move the research to market is important to the future of the paving industry. Universities should play a significant role in future research, development, and deployment efforts. The evaluation systems for faculty at universities needs to be altered to reward professors for their “contributions to society” not just securing the latest high technology, nationally competitive research project.

With fewer dollars and a limited public agency workforce available to construct, reconstruct, rehabilitate, and maintain the highways, design and building of the pavements must be smarter, time in the work zones must be shorter, and the pavements constructed must last longer. The process must be “smarter, faster, and provide a longer life pavement.” A mantra for accelerated construction of “get-in, stay-in, and get-out and stay-out” has application to this industry.