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Publication Number: FHWA-HRT-05-052
Date: September 2005
For generations, concrete has been the workhorse for long life, dependable pavements. By generally performing well for many years beyond their original design life, concrete pavements have provided a substantial return on taxpayers' investments.
For most of the 20th century, the same materials-aggregate, portland cement, and water-were used in concrete for pavements, with only minor refinements. It was a fairly forgiving, high-tolerance formula. Mixes made with portland cement and high-quality aggregates allowed some variations in subgrade quality, construction practices, and other variables without sacrificing pavement performance. For generations, too, the emphasis was on constructing new pavement miles, and the industry had the luxury of keeping traffic off new concrete pavements for several days, even weeks, while the concrete developed its internal maturity and design strength.
Over the past 15 years, however, the concrete pavement industry has experienced more changes than in the preceding 80 years, and these changes are turning the process of building concrete pavements on end. Some of the ongoing environmental, social, and economic trends affecting the industry are that:
In this environment, the old system for constructing concrete pavements no longer works. In recent years, pavement failures unheard of 25 years ago have occurred. The industry has tried to stay ahead of the trends, but improvements in concrete pavement construction have been incremental, inconsistently implemented, and sometimes only marginally successful. In the coming decades, changes such as those described above will only increase, as will the consequent challenges for the concrete pavement community.
To achieve concrete pavement's full potential in the 21st century, the industry should respond to these trends soon with dramatic, even revolutionary, improvements. The improvements cannot be piecemeal. They should be the result of a carefully developed and aggressively implemented strategic plan for research and technology transfer. The CP Road Map is that plan.
The following sections describe in more detail the trends listed above. Changes occurring in the concrete industry are interrelated, exacerbating the resulting challenges.
Perhaps the most significant change in recent years is in concrete pavement mixtures. Mixtures are becoming more and more complex and are no longer so forgiving.
Many factors have led to the use of new materials in concrete. For example, to make fast-track or other special-use mixes, chemical additives are included commonly now in mix designs. Fly ash and slag also are being added to mixtures to replace some of the portland cement and enhance certain concrete mix characteristics, like reduced alkali-aggregate reaction and increased resistance to attack by sulfates in soil and water.
Ironically, though, new materials or additives that solve one problem can cause other, unforeseen problems, often related to materials incompatibility. The host of aggregate, cement, and mineral and chemical admixture sources from which to choose makes it difficult to develop mix designs that perform consistently; concrete can fail with only moderate variations in materials from supplier to supplier. There is no longer any room for error. In addition, complex mixtures that perform satisfactorily under lab conditions can be less predictable under actual field conditions.
The industry needs improved, reliable quality control systems for ensuring predictable, reproducible performance of today's complex mixes, pavement after pavement after pavement.
Pavement users (including funding providers) require a certain level of pavement functionality and performance. Motorists are demanding quieter and smoother pavements that improve the driving experience and do not adversely affect the communities they abut. Pavement surfaces should be perfected to eliminate joint noise and tire whining, while continuing to provide a safe level of friction and reduced tire hydroplaning and spraying when wet.
Transportation agencies, concrete pavement engineers, materials providers, and contractors need new tools and strategies for better understanding and controlling pavement surface characteristics such as smoothness, friction, noise, spray and drainage, rolling resistance, and visibility. Traffic noise, too, is a growing problem in urban areas. The industry must understand concrete pavement's role in this phenomenon and provide balanced solutions.
In addition, motorists have no patience for long road closures or work zone delays. The speed of completing construction, repair, and rehabilitation work has become a critical issue, with mottos like “fast-track construction” and “get in, get out, and stay out” becoming common industry themes. Needed solutions include better use of available material on the roadway and quicker and timelier inspections.
In the past 15 years or so, with most of the highway system built and in service, the industry's emphasis has changed from constructing new pavements to repairing and rehabilitating existing ones. According to a recent study by The Road Information Program, pavements on 25 percent of the Nation's major metropolitan roads-interstates, freeways, and other principal arterial routes-are in poor condition.(1) In the next few years, more than 25,000 miles of the Nation's highways will require serious attention. Up to 75 percent of pavements already identified as needing improvement are light-service pavements.
To remain competitive, the concrete pavement industry should be able to deliver affordable alternatives for a variety of road repair, maintenance, and rehabilitation needs. What truly is needed is the next generation of a mix of fixes: a menu of viable, cost effective concrete pavement solutions that provide concrete's durability and strength for the short or very long term.
The industry is already experimenting with different types of concrete overlays-bonded, unbonded, and whitetopping-each distinguished by the type of existing pavement it covers. Because of cost, time required for construction, and misconceptions about overlays, however, these alternatives nationally have had only minimal impact. The industry needs new overlay design approaches, lower cost strategies, and faster construction methods.
The mix of fixes could also include, for example, two-lift construction, in which a thin overlay of superior concrete mixture is placed on a thick layer of lower quality concrete; stop-gap rehabilitation projects; and staged improvements, in which short-term pavements are later used as subbase when their design life is over. Some solutions could focus on improving pavement foundations so that thinner pavements can provide the same level of service as traditional, thicker pavements.
Different mix designs for different solutions exacerbate quality control challenges related to materials compatibility and fast-track construction environments.
The level of funding available for pavement repair and rehabilitation is not keeping pace with needs. In 2004, State and local funding for road and bridge improvements was down 18 percent from 2002 levels, and restraints on domestic budgets are not likely to end anytime soon. This directly relates to the need for a full array of concrete pavement products to provide an affordable mix of fixes that allows agencies to properly distribute limited funds.
Static or reduced public agency funding is spurring the transfer of roles and responsibilities from State and local transportation agencies to the construction industry. This transfer includes a shift from method specifications to end-result, or performance, specifications. Mix designs, quality control, end-result testing, warranties, design-build, etc., require more expertise from the contractor than ever before. Contractors and agencies alike need better tools for monitoring, controlling, and ensuring desired pavement performance.
These tools include software for integrating mix designs with structural designs and construction inspections. They include software for conducting high-speed analyses and prediction of mix performance during the critical 72-hour period when concrete operations have such a significant impact on overall pavement performance. They include new equipment and testing methodologies that will help control the product during construction, reducing variability. It is difficult to reduce costs while maintaining predictable service. The industry needs better methods and tools for identifying and addressing cost issues, testing different designs, conducting life cycle cost analyses, and using marginal materials.
Pavements also should meet ever-more demanding environmental challenges. For example, rainwater runoff issues are driving the need to develop porous pavements for specific applications, like parking lots and curb and gutter. In cold climates where snow is an issue, the salt brine placed on pavements to improve safety actually may cause premature damage to the concrete.
Quality building materials are harder to come by, and new sources are not being brought online, increasing the use of marginal materials. The cement industry, under pressure to reduce harmful byproducts of portland cement manufacture, is increasing its use of supplementary cementitious materials, including recycled materials like fly ash (captured from exhaust gases of coal-burning electricity generating plants) and slag (tapped from the waste that floats to the top of iron blast furnaces).
As described earlier, using these new or marginal materials requires advancements in mix design, new construction methods that incorporate marginal mix designs, and, especially, quality control systems to ensure that satisfactory performance can be reproduced reliably.
Pavements are the backbone of the Nation's transportation system and are essential to its economic well-being. Virtually all of the goods produced and sold in this country travel on the Nation's highways. From 1970 to 1998, the average daily highway traffic volume increased 130 percent, while average daily loading increased 580 percent.
By 2020, the U.S. population is predicted to grow by 50 million people. Vehicle travel is expected to increase by about 42 percent and heavy truck travel by 49 percent, putting even greater stress on the Nation's roadways. Without additional lane capacity, and with projected increases in truck traffic, a lane-mile of pavement built in 2015 will have to carry 70 percent more trucks than a lane-mile built in 1995.
Clearly, concrete pavements can carry heavy-duty truck traffic, but even this area has room for advancement. For example, the industry needs improved foundation designs that allow for better assignment of loads through the slab and better drainage mechanisms.
As congestion increases, access to facilities for constructing, maintaining, and rehabilitating pavements will become more difficult. Automobiles, trucks, the pavement, and neighborhoods abutting the pavement will all have to coexist. This will have a dramatic impact on pavement programs, including initial pavement selection, speed of construction, rehabilitation and maintenance strategies, and budgets. Developing concrete pavement systems to address these needs is a critical challenge.
The bottom line is that one size no longer fits all. The concrete pavement industry must reinvent itself and develop a generation of pavement solutions for the 21st century.
What exactly would this new generation of solutions look like? How would they be developed? With AASHTO, ACPA, FHWA, PCA, State agencies, universities, and other organizations working relatively independently on specific challenges, how can stakeholders agree on the answers, establish common priorities, reduce duplication of effort, and make the solutions a reality?
To answer these questions, FHWA needs a unique long-term research plan with the following characteristics:
The following chapters describe how such a plan was developed, provide an overview of the resulting CP Road Map, and outline an innovative research management plan for conducting the research.
Topics: research, infrastructure, pavements and materials
Keywords: research, infrastructure, pavements and materials, Concrete pavement, concrete mix design, pavement construction, pavement design, pavement performance, pavement smoothness, equipment automation
TRT Terms: research, facilities, transportation, highway facilities, roads, parts of roads, pavements