Concrete: Ready For The Road Ahead

Sept. 28, 2010

Rising oil prices, the war in the Middle East, recession worries, and the future political leadership of this nation continue to dominate the headlines all around us, so much so that it seems like there's little time or space for other important news to be reported.

Rising oil prices, the war in the Middle East, recession worries, and the future political leadership of this nation continue to dominate the headlines all around us, so much so that it seems like there's little time or space for other important news to be reported.

But there's another story that needs to be told. It's the story of our nation's surface transportation infrastructure, which is facing the three-fold challenges of capacity, condition and cost. Oil and fuel prices have a direct impact on construction costs, which underscore the importance of using durable paving materials that are less prone to these challenges.

The condition of our nation's surface transportation network is getting worse, and with programs whose funding levels are below what's needed to meet even the most critical needs, there seems to be few options available to restoring the network to proper condition. Meanwhile, congestion is plaguing our nation's highways, airports, streets and roads, as a growing population and increased traffic place more demands on our system. In turn, this necessitates more rehabilitation and expansion, which requires more funding.

We think there's a better way than the status quo. Breaking free of the current crisis will require a fresh look at the way things are done, including better alternatives to the cycle of frequent maintenance, repairs and replacement associated with asphalt pavements. The life cycle cost advantages of concrete pavement are well known, but with rising oil prices, concrete is competitive on first costs, too.

But there's more. The American Concrete Pavement Association is working on a number of important initiatives aimed at improving quality, reducing costs and generally making concrete pavements even more beneficial to agencies across the nation.

Guiding the Mixture Design, Proportioning Process

One example is in the form of the ACPA helping contractors develop better mixtures. Over the years, there has been a shift in the responsibility for designing and proportioning concrete mixtures, so increasingly contractors are expected to take on this responsibility.

Minimizing variability will improve quality, and so the concrete pavement and cement industries — in collaboration with the Federal Highway Administration and the National Concrete Pavement Technology Center (CP Tech Center) — are authoring a step-by-step manual to guide concrete paving contractors through every step of the mixture design and proportioning process.

ACPA and the Portland Cement Association, working with the CP Tech Center, are writing the guide, which will be reviewed and guided by a contingent of practitioners from across the country. The collaborative effort is one significant step closer to completion: The contents have been outlined, authors have been named, and the panel of reviewers has been established.

The publication, "Design and Proportioning of Concrete Paving Mixtures," is a comprehensive range of information that covers key characteristics and effects of the interactions among cementitious materials, aggregates, mixing water, and chemical admixtures.

The Next Generation Concrete Surface

The Association has invested time and resources in the area of pavement surface characteristics, which are not only the key to a safe, smooth driving surface, but are also important in urban areas where tire/pavement noise is a concern.

ACPA's Next Generation Concrete Surface (NGCS) is just one of the key deliverables from a three-year research initiative focused on concrete pavement surface characteristics and tire/pavement noise.

NGCS continues to show promising results, based on recent testing conducted more than six months after the projects were originally constructed. The new surface validates proof-testing research conducted at Purdue University and confirms that blade width and spacing are not the controlling factors in noise generation. The determining factor is the resulting profile or smoothness of the fins. Equally important, NGCS test results represent the concrete paving industry's progress in achieving quieter concrete pavement surfaces. To date, two sites have been tested: In Minnesota, two 500-foot lanes on Interstate 94,part of MnROAD's test area, just northeast of St. Paul; and, in Illinois, a single, 1,200-foot travel lane on Interstate 355 in suburban Chicago.

Initial test results last fall revealed the NGCS tested at 100.1 dBA in Minnesota and 100.5 dBA in Chicago. Testing earlier this month showed an adjusted noise level of 100.7 dBA on the sections in Minnesota, a decrease of almost four decibels, which likely is associated with the fin breakage (a desired and expected effect). Chicago readings showed readings were in about the same range — 100.7 dBA in the fall and 100.9 earlier this month.

The 100-dBA reading is very competitive with most quiet pavements of all surface types available today.

Improving Pavement Design

ACPA is also directly involved in efforts to take some of the guesswork and subjectivity out of pavement design.

The Mechanistic-Empirical Pavement Design Guide (M-E PDG) is just one example of how ACPA is directly involved in improving pavement design. The M-E PDG is a state-of-the-practice tool that automates and standardizes the process of pavement analysis and design. It represents a drastic departure from the empirically based procedure currently in use by most agencies in both the level of required inputs and the mode of calculation.

It also integrates pavement design, materials selection, construction, and pavement management systems, according to the Federal Highway Administration.

It offers an easier, more objective way for designers and others to estimate pavement performance and potential distresses. In the near future, officials also anticipate the ability to customize the program with their specific traffic, materials and environmental conditions.

ACPA is conducting extensive trial runs of the M-E PDG, which was recently approved for implementation by the American Association of State Highway and Transportation Officials.

ACPA is recognized as one of the first stakeholder organizations to take this step to help users better understand and implement the M-E PDG as a tool for designing and optimizing concrete pavements.

Anticipated Products from ACPA's Trial Runs Are:
  • A sensitivity analysis of features accounted for in the design guide. These will identify the key variables that the concrete pavement industry should pay attention to and influence during construction. This analysis also will help the concrete pavement industry identify how the recommended design will affect construction practices.
  • Graphs (based on the trial runs) to show users how specific conditions will affect pavement thickness. The graphs will represent a catalog of features, which is an attempt to put the guide's recommendations into easy-to-understand terms.

This effort, as well as the work by a large number of other stakeholders, is expected to lead to greater acceptance and broader implementation of this useful and practical design tool.

In addition to the M-E PDG, ACPA also has developed a useful tool that can be used in highway, street and road design. StreetPave uses thickness design technology and engineering analyses to produce optimized concrete pavement thicknesses for municipal, county and state highways, streets and road facilities.

It includes an asphalt cross-section design process (based on the Asphalt Institute method) to create an equivalent asphalt design for the load-carrying capacity requirement. A "Life Cycle Cost Analysis" module allows you to perform a detailed cost/benefit analysis and make informed decisions on your pavement design project.

Reaching People When, Where It Matters Most

ACPA has expanded its reach with education and training programs that include both traditional, classroom-style training as well as web-based training that deliver information about a wide range of topics related to concrete pavement design, construction and rehabilitation.

In the first five months of this year alone, ACPA has provided training to more than 1,000 people representing agencies, consulting firms, contractors, and others. Equally important, the low cost, varied options and other aspects of the training make participation easy, convenient and affordable.

These are just a few examples that represent ACPA's current activities. ACPA is also addressing timely topics such as sustainability, pavement optimization, innovative contracting, jointing practices, and a number of other important issues to agencies, contractors, consultants, and the transportation-construction community overall.

Although economic and geopolitical issues may dominate the headlines today, the American Concrete Pavement Association is sharply focused on averting a crisis with our surface transportation infrastructure. As some have said, the condition of our nation's infrastructure threatens to reduce the United States to third-world status.

For our part, we will continue to improve our products and processes to provide the best value, in both the short and long term. We urge anyone with an interest in concrete pavements to get involved and stay involved with ACPA, not only to influence the direction and scope of programs, but also to take advantage of opportunities that lie ahead.