Handling it differently

July 18, 2005

What’s new in highway materials in Europe? Does Europe employ superior materials in highway construction, materials unknown in the U.S? Do the Europeans have new test methods and specifications that could improve transportation construction here in the U.S.? Or do they have approval processes or contracting methods that might be adopted in the U.S.?

What’s new in highway materials in Europe? Does Europe employ superior materials in highway construction, materials unknown in the U.S? Do the Europeans have new test methods and specifications that could improve transportation construction here in the U.S.? Or do they have approval processes or contracting methods that might be adopted in the U.S.?

Those questions and the need to constantly improve our transportation systems resulted in a scanning trip to four European countries: England, Denmark, Germany and the Netherlands. We found much of what we already knew, few new materials, but more than a few eye-opening surprises.

The International Technology Scanning Program, lead by FHWA and AASHTO, sends teams of experts to a variety of countries worldwide to investigate innovative technologies, management practices, organizational structure, program delivery and financing. Our Superior Materials scan, composed of three FHWA members (Keith Herbold, scan co-chair, Laurin Lineman and Max Grogg), four AASHTO members (Lon Ingram, scan co-chair, Kansas DOT; Jimmy Brumfield, Mississippi DOT; Mark Felag, Rhode Island DOT; and this author, Tom Baker, Washington State DOT) and two consultants (Robert Rasmussen, report facilitator and Ted Ferragut, implementation specialist).

The first surprise from the scan tour was that there were no surprises in superior materials—no magic material bullets. Given global communication, international trade and the constant sharing of information this could have been expected. Worldwide competition drives the private sector to rapidly adopt and put new materials to use.

Rather than materials, the key findings of the scan tour were in new construction techniques, new testing methods, different acceptance processes, an interesting move toward European Union standardization and innovative research programs.

Construction techniques

Twin-Layer Asphalt—The noise-reducing abilities of porous asphalts are well known, but there are difficulties with using them on lower-speed facilities. At high speeds, the traffic draws sand and dirt out of the pores, effectively resulting in a “self-cleaning” surface. At lower speeds, typical of many city streets, this self-cleaning action does not occur.

A twin-layer paving system uses a larger stone porous matrix in a lower lift, covered by a porous mix with a smaller aggregate for the wearing course. The wearing surface clogs first and then can be cleaned by vactoring, keeping the lower lift open and free draining.

Low-Temperature Asphalt Mixes

Germany uses a variety of polymers and mineral admixtures to modify hot-mix asphalt (HMA) for placing at lower temperatures than conventional HMA. Low-temperature paving results in lower emissions and saves energy.

New testing methods

Torque Bond Test—We assume that HMA pavement, made of many layers, acts as a unified whole, much like plywood. But our “glue,” tack coat, is only assumed to work—we don’t have a performance test to check the bond between HMA paving layers. The Highways Agency in the United Kingdom developed a test to evaluate the in-place bond between HMA layers. This simple performance test cores the pavement to below the layer interface, attaches a metal rod to the core and then applies a torque through a torque wrench attached to the metal rod. The force required for failure relates to the performance of the bond, as does the location of the failure. For a well-bonded material, failure occurs within the underlying material and not at the bonded interface.

Accelerated Pavement Stripe Wear Tester (also known as “The Wheel”)—Due to the expense and logistics associated with field testing of lane marking (striping), Germany has developed a laboratory facility for accelerated lane-marking evaluation. This facility is capable of evaluating tape, temporary paint and permanent paint markings. Since the facility began testing in 1989, nearly 2,000 materials have been tested. This specification can be found in CEN 13197.

Pulse (Active) Thermography—Composite laminate strengthening of bridges for earthquake restraint is now common.

The Building Research Establishment (BRE) in the United Kingdom demonstrated a new field technique to determine the bond effectiveness of composite laminate repairs. This technique employs an active heat source that applies a heat pulse to the composite laminate and the thermal signature clearly delineates bonded and unbonded areas.

Materials acceptance processes

Materials acceptance in the U.S. relies primarily on method specifications along with a growing trend toward performance specifications. State departments of transportation commonly test materials to set specification to determine acceptance. Throughout the countries we visited we found strong use of performance specifications, warranties and independent materials evaluation.

Unique entities, for which there are no clear counterparts in the U.S., such as BRE and Transport Research Laboratory of the United Kingdom; Danish Road Institute; Dienst Weg-en Waterbouwkunde; and the Information and Technology Centre for Transport and Infrastructure of the Netherlands, evaluate materials for highway projects. These organizations, fiercely independent, well respected and trusted within the highway community, work between government and industry. They commonly have large boards of directors but no stockholders. They exist to test and evaluate materials, beholden neither to government nor to industry.

The governments and industry agree on specification, usually performance based, and the manufacturers submit their materials to these independent labs for evaluation. Those that pass are considered “fit for purpose.” Common steps within most of the evaluation and certification processes are:

  1. The process begins with the manufacturer collecting and documenting data on material properties, behavior and performance. The manufacturer has no incentive to shortcut this step, since the remaining steps require additional investment, thus they want to prove to themselves that the material will not fail.
  2. The vendor approaches the independent evaluating organization, presenting the existing data and entering into a contract for testing.
  3. If the material falls into a new category, it may require a preliminary assessment of functional requirements for that category—what properties should be tested to ensure the stated performance. This sometimes involves formation of a committee of experts in the respective field.
  4. The material is tested according to the specifications. If it passes, it is certified.

European Union Standardization

The European Union (EU), through its various commissions, boards and associations, promotes trade and commerce across borders, and the transportation and highway construction fields are no exception. By effectively eliminating barriers to free trade, there is now pressure for manufacturers and owners to move together towards standardized functional specifications rather than conventional prescriptive specifications. The Comité Européen de Normalisation (European Standardization Organization), or CEN, focuses on standard materials and specifications, while the European Organization for Technical Approval deals with unique and unusual materials, construction techniques and specifications. Within the CEN there are quality classifications for varying thresholds and tolerances on the materials test results, allowing governments to select the desired level of quality for any given application. The quality level is an EU member choice; the materials and test standards are EU standards.

While the CEN standardization process is moving forward, it is not without difficultly. As part of the harmonization process, each member country must debate the various details of their previously independent specifications. A further consideration is the differences that arise in definitions and language (the official language for the specifications is English, although French and German versions also will be approved for use). Standardization brings new markets, but at the price of removing (sometimes) artificial protections of existing markets. The development of the CEN specifications can be viewed as a “reverse AASHTO.” While AASHTO has produced guide specifications that can be optionally adopted (and/or modified), the EU process is in the process of combining their current specifications into a common binding spec.

Innovative research programs

The Netherlands “Roads to the Future” project introduced a novel approach to explore long-range solutions to meet future highway demands. A contest was held with a number of predefined highway functional requirements (e.g., noise reduction or lane-closure paving windows). To meet these demands, manufacturers were invited to offer solutions, no matter how unconventional. The tremendous response by the manufacturing community surprised the highway agency, which selected a small number of proposals for further evaluation on a predefined test section. Four different techniques resulted, including options with precast HMA surfaces that were laid down off of rolls (like carpeting). These pavements could be manufactured under controlled conditions, placed on the highway and then removed and returned to the manufacturing plant for controlled rehabilitation.

Done as they’re told

The Netherlands highway agency set a performance level on emptying garbage cans at highway rest stops. At any given time, when inspected, garbage cans could be no more than half full. The agency figured this requirement would encourage frequent emptying of the garbage cans at the highway rest stops—not so. Instead, the private contractor sent one crewmember around in a small pickup truck and had them remove just enough garbage to reduce the garbage can to half-full-performance-based specification met. This resulted in extending the time between total emptying of the garbage cans, saving money for the contractor. Only once a week or more would the big trucks come and haul away all the garbage in the cans. The unintended consequence? Garbage would sit in the cans for extended periods of time, resulting in voluminous quantities of “stink,” especially in the summer months.

The American way

The key to scan tours is implementing what you learn. Implementation is not simply translating the lessons directly to the U.S., as noted by Jan van der Zwan of the Netherlands when he said, “Understand what we do, but don’t copy it. Unless, of course, you are the Netherlands.” The lessons learned must be translated into our culture, particularly our highway construction culture.

A full implementation plan is under way. The Torque Bond Test is being shared and studied by several groups, including the State Pavement Technology Consortium, a pooled-fund effort by Caltrans, Minnesota DOT, Texas DOT and Washington State DOT. FHWA and AASHTO funded a feasibility study, currently underway, to more fully investigate the Accelerate Pavement Marking System Tester. A team is headed to Spain to meet with the Spanish government and with AETEC, constructors and operators of the Spanish Accelerated Pavement Marking Tester. Proposals are shaping up for trying a “Roads to the Future”-type research project in the U.S. Pulse thermography is under investigation in Washington State. The fruits of the “boot camp/summer camp” scan tour are on the way.

About The Author: Baker is a state materials engineer for the Washington State DOT, Olympia, Wash.

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