Fhwa Program Combats Asr

Preventing and mitigating alkali-silica reactivity (ASR) in portland cement concrete pavements and structures is the focus of a four-year, $10 million

Preventing and mitigating alkali-silica reactivity (ASR) in portland cement concrete pavements and structures is the focus of a four-year, $10 million Federal Highway Administration (FHWA) initiative, established and funded by the 2005 Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU). This new highway concrete technology program is designed to increase concrete pavement and structure durability and performance, as well as reduce life-cycle costs through the prevention and mitigation of ASR, says Gina Ahlstrom of FHWA’s Office of Pavement Technology.

ASR occurs when silica in some aggregates and alkalis in concrete combine with water to form a gel-like substance. As the gel absorbs water and expands, it causes cracking in the concrete. Over time, the cracks promote other modes of distress, such as freeze/thaw damage or corrosion, leading to permanent damage and even structural failure.

A Benchmarking Workshop was convened in Chicago by FHWA to gather stakeholder input on the new ASR program. The 74 attendees Û representing academia, industry, state departments of transportation, FHWA, and other federal agencies Û discussed the current state of the practice and areas where further development and deployment of ASR prevention, identification, and mitigation techniques are necessary. Participants noted, for example, that field identification of the condition is difficult and awareness of its pervasiveness is lacking, since ASR detection typically is not included in standard pavement or bridge inspection protocols. Thus, inspectors require an easy-to-use, fast, and reliable field test to identify ASR.

Also cited was the need for a fast and reliable testing method to identify potential for ASR in concrete mixes proposed for transportation structures. Workshop participants strongly emphasized the importance of increasing awareness of ASR among agencies and contractors, as well as improving the decision-making process to prevent its occurrence in new construction.

The workshop provided a good opportunity to bring stakeholders together and put both the state of the problem regarding ASR and the state of the science for prevention and mitigation on the table, says workshop participant Lizanne Davis of FMC Corp. The new ASR program will jump start education and awareness of the problem, get new technologies into the field, and offer the opportunity to extend the life cycle of concrete pavements and structures.

Adds participant Cecil Jones of the North Carolina Department of Transportation, The workshop was instrumental in bringing the right group of people together to talk about ASR for the sake of a new program offering the opportunity to build on previous work done by the Strategic Highway Research initiative. Implementation will be crucial in moving the program forward.

Measures related to issues highlighted at the benchmarking workshop are central to the new ASR program. Rapid test and evaluation protocols, using materials such as lithium and fly ash in concrete mix designs, will be developed for the use of transportation agencies in selecting procedures to prevent ASR in new structures and pavements. Also high on the program agenda is developing ASR-mitigation techniques for existing pavements and structures, as well as determining methods to evaluate the condition of ASR-afflicted concrete. Work now underway is expected to provide protocols in 2008. Moreover, the program will develop a system for tracking bridges and highway pavements affected by ASR. Technology transfer efforts will include compiling informational materials, such as training and technical documents, and launching an ASR Web site to display program data and findings.

Additionally, taking technologies into the field is a program priority. To that end, funding will be provided to states interested in field trials or demonstration projects for pavements, bridges, or other highway structures such as median barriers or retaining walls. Projects can employ technologies for either ASR prevention in new concrete or its mitigation in existing structures.

An ASR Stakeholder Technical Working Group (ASR TWG) has been formed to monitor program implementation and provide technical assistance. TWG members, representing state transportation bodies, academia, industry, and various federal agencies, held their first meeting in April.

More ASR program information or details regarding the hosting of a state field evaluation or demonstration project can be obtained by contacting FHWA’s Gina Ahlstrom at 202/366-4612 (email: [email protected]). Serving as FHWA contact for the program’s applied research component is Paul Virmani at 202/493-3052 (email: [email protected]). The final ASR Benchmarking Workshop report is available online at www.fhwa.dot.gov/pavement/concrete/asr.cfm.

This report was adapted from an article in Focus, April 2007, published by the U.S. Department of Transportation, Federal Highway Administration.