Advanced High-Performance Materials for Highway Applications: A Report on the State of Technology

Chapter 1, Introduction

This report presents a review of the availability of advanced construction materials that show promise for routine pavement construction and rehabilitation on the Federal-Aid Highway System. The Federal-Aid Highway System includes over 200,000 mi (321,869 km) of interstate and primary highway system in all 50 States, the District of Columbia, and U.S. territories. The highway pavements on this system consist of asphalt pavements (also referred to as asphalt concrete [AC] or flexible pavement) and concrete pavements (also referred to as portland cement concrete [PCC] or rigid pavements). The pavement type denotes the material used for the surface layer, the wearing course of the pavement. Each pavement type is built up of layers, starting with the existing subgrade with each successive layer utilizing better quality material.

The most costly layers and the layers that are designed and constructed to be the most durable layers are the surface layers - consisting of AC or PCC.

The generic composition of typical AC is as follows:

• Asphalt binder - 6 to 8 percent by volume.
• Aggregate (graded) - 85 to 90 percent by volume.
• Filler material - 2 to 3 percent by volume.
• Air - 2 to 4 percent by volume.

One lane-mile (1.6 lane-kilometers) of AC pavement construction can require about 2,400 T (2,177 t) of AC for a surface layer that is 6 in. (150 mm) thick.

The generic composition of typical PCC is as follows:

• Cementitious materials (portland cement, fly ash, slag) - 10 to 14 percent by volume.
• Aggregate (coarse, intermediate, fine) - 62 to 68 percent by volume.
• Water - 14 to 18 percent by volume.
• Air - 4 to 8 percent by volume.
• Admixtures - very small amounts.

One lane-mile of PCC pavement can require about 4,800 T (4,354 t) of concrete for a surface layer that is 12 in. (300 mm) thick. Also, 1 lane-mile of continuously reinforced concrete pavement (CRCP) can require about 100 to 120 T (91 to 109 t) of steel. In U.S. northern and coastal areas, the steel in CRCPs and the steel used at joints in jointed concrete pavement need to be protected to minimize the potential for corrosion that can lead to early failures of CRCPs and jointed pavements.

As indicated, every year large amounts of aggregate materials and manufactured materials are needed to support highway construction and rehabilitation in the United States. However, the poor availability of good-quality aggregates in many parts of the country and the increasing financial and societal costs to produce the needed manufactured materials are creating a concern for planners and engineers. It is, therefore, important that new and improved sources of highway construction materials be developed that will result in improved performance of the highway system, be cost-effective, and incorporate sustainable technologies. Sustainability consideration in highway construction and rehabilitation is of recent origin. However, its impact on the well-being of the Nation's highway infrastructure cannot be underestimated, as discussed next.

Sustainability and Availability of Sound Materials - A National Concern

In many parts of the United States, supply of acceptable quality aggregates is very limited and aggregates are imported from neighboring States, Canada, or Mexico. In addition, the production of portland cement is very energy intensive and also accounts for high carbon dioxide (CO₂) emissions. Expectations for the future are that restrictions will be placed on cement production and the cost of cement production will rise to meet environmental regulations. Similarly, the availability of asphaltic binders is dependent on the supply of oil and oil industry efforts to maximize use of oil refining by-products. As a result, it is expected that the cost of asphalt binders of highway pavement grade will remain high, and the supply is expected to be inadequate to meet U.S. demand.

Cost of construction materials continues to increase every year. In addition, use of marginal materials results in early development of pavement distress, requiring more frequent repairs and rehabilitation and associated lane closures and traffic congestion in high-volume traffic areas. Traffic congestion also increases the potential for construction-zone accidents and increased levels of environmental pollution related to automobile emissions. Therefore, there is a strong desire in the United States to optimize the use of materials currently used for highway pavement construction and to seek advanced materials that are cheaper, better performing, and less damaging to the environment.

Needs for Advanced High-Performance Materials

The needs for seeking advanced highway construction materials include:

• Reduced costs - get more lane-miles constructed or rehabilitated for a given constrained budget.
• Conservation of resources - support national efforts to create sustainable solutions to minimize impact of construction on the environment.
• Reduced ecological footprint.
• Extended service life.
• Optimized use of locally available materials.
• Achieving environmental benefits - reduced carbon footprint, reduced congestion-related emissions.
• Reduced work zone - related traffic delays and safety concerns - use materials that reduce the potential for early failures.

Historical Evolution of Highway Construction Materials

Today, the U.S. Federal-Aid Highway System consists of the original Interstate Highway System and the U.S. Primary Highway System, totaling over 200,000 mi (321,869 km). The pavements along this system have undergone one or more cycles of rehabilitation or reconstruction. The U.S. Federal-Aid Highway System is one of the best highway systems in the world and provides for efficient movement of people, goods, and services very cost-effectively. However, due to the ever-increasing traffic and environmental damage, thousands of miles of the system require rehabilitation or reconstruction every year. In recent years, over $30 billion has been spent annually for the reconstruction, rehabilitation, and maintenance of the Federal-Aid Highway System. Traffic volumes have increased significantly in most metropolitan areas with some urban highways carrying in excess of 200,000 vehicles per day.

The high volumes of traffic, limited availability of funds for highway improvement, diminishing raw materials, and concerns related to the environmental impact of construction and of poorly performing highways necessitate an urgent evaluation of technologies to improve the performance of Federal-Aid Highway System pavements by ensuring that pavements are longer lasting, smoother, safer, and environmentally friendly.

The currently used materials for pavement construction can be classified as follows:

1. Natural (Raw) Materials.
   1. Aggregates.
   2. Lake asphalt.
   3. Natural resins.
2. Manufactured (Processed) Materials.
   1. Metallic materials (steel, aluminum, zinc).
   2. Ceramic-based materials (portland cement, natural pozzolans).
   3. Visco-elastic materials (AC).
   4. Industrial by-product materials (fly ash, slag, silica fume).
   5. Other waste products (crumb rubber).
   6. Chemical admixtures for concrete.
   7. Fillers for AC.
   8. Epoxies and polymers.
   9. Fibers and fiber-reinforced polymers.
   10. Synthetic aggregates - typically, lightweight and slag aggregates.
3. Composite Manufactured Materials
   1. PCC.
   2. AC.
   3. Coated or clad steels.

This white paper reviews the availability of advanced construction materials for highway application to improve or replace the above-listed, conventionally used construction materials. These advanced construction materials can be categorized as follows:

1. New/Innovative materials to replace current materials.
2. New/Innovative materials that are less expensive.
3. New/Innovative materials that result in longer service life.
4. New/Innovative materials that result in sustainable solutions.
5. New/Innovative materials that improve the properties of marginal materials.
6. Waste and recycled materials that are optimized for use.

The criteria for including specific advanced construction materials in this white paper include the following:

1. The materials were recently introduced (have been less than 5 years in the marketplace) and are not widely used.
2. The materials are under development.

The advanced materials identified include the following:

1. Cementitious Materials.
   1. Performance-specified cements.
   2. Next-generation sustainable cements.
   3. Eco-friendly cements.
   4. Energetically modified cement.
2. Concrete Materials.
   1. Engineered cement composites (ECCs).
   2. Titanium dioxide - modified concrete.
   3. Pervious concrete.
   4. Self-consolidating concrete.
   5. Sulfur concrete.
   6. Autoclaved aerated concrete.
   7. Geopolymer concrete.
   8. Hydrophobic concrete.
   9. Ductile concrete.
3. Asphalt Binder Materials.
   1. Sulfur-extended asphalt.
   2. Bio-derived asphalt binders.
   3. High modified asphalt binders.
4. AC Materials.
   1. Warm asphalt mixtures.
   2. Perpetual asphalt pavement systems.
   3. Porous asphalt pavement.
   4. Recycled asphalt shingles.
5. Metallic and Polymer Materials.
   1. Vitreous ceramic coatings for reinforcing steel.
   2. Fiber-reinforced polymer bars for CRCPs.
   3. Fiber-reinforced polymer dowel bars.
   4. Zinc-clad dowel bars.
   5. Microcomposite steel for dowels and tie bars.
6. Aggregate Materials.
   1. Synthetic aggregates.
   2. Manufactured aggregate using captured CO₂.
   3. Materials that allow internal concrete curing.
7. Other Materials.
   1. Ultra-thin bonded wearing course.
   2. Advanced curing material.
   3. Workability-retaining admixture.
   4. Concrete surface sealers.

Summary

In the United States, there has been continuous interest and effort in developing improved highway construction materials. Until recently, the development of improved materials was focused at improving specific properties of locally available materials by using additives (admixtures, extenders, modifiers). There was no strong impetus to seriously consider replacing conventional construction materials with new materials. However, it has now been recognized that the age of limitless construction materials and the use of conventional materials in their present form is fast coming to an end, and new technologies need to be developed to continue to support the rehabilitation and reconstruction of pavements along the Nation's highway system. Today, concerns about limited availability and sustainability are driving the search for new and advanced materials for highway construction.

More Information

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Contact

Sam Tyson
Office of Asset Management, Pavement, and Construction
202-366-1326
E-mail Sam