Gina Ahlstrom, Federal Highway Administration
Alkali-silica reactivity (ASR) is a deleterious reaction that can occur in concrete mixtures when alkalis in the cement and other pozzolanic materials react with siliceous aggregates and expand when exposed to moisture. The Federal Highway Administration (FHWA) has initiated an ASR Development and Deployment Program in response to the SAFETEA-LU legislation. A comprehensive program, which is focused on preventing and mitigating ASR, has been developed to address states’ needs and provide them with tools to address ASR in bridges, pavements, and other highway structures such as median barriers or retaining walls. This article outlines the various tasks of the ASR Development and Deployment Program.
Task Area 1: Understanding the ASR Mechanism Process for Mitigation
Applied research will be conducted to quantify competing chemical reaction rates between various constituents in the concrete mix and the environment. The goal of this research is to develop a model that can predict a mix design that is resistant to ASR.
Task Area 2: Develop Testing and Evaluation Protocol
Protocols have been developed for engineers and transportation practitioners to provide a step-by-step process on the current best practices of ASR prevention and mitigation. The protocols are titled “Determining the Reactivity of Concrete Aggregates and Selecting Appropriate Measures for Preventing Deleterious Expansion in New Concrete Construction” and “Diagnosis and Prognosis of Alkali-Silica Reaction (ASR) in Transportation Structures.”
Currently available rapid test procedures have varying levels of confidence and most have limitations. Research will be conducted to identify recent worldwide advances in rapid test methods, identify the most viable and effective test methods, determine their limitations, assess the required test period, and refine or modify these methods. If a rapid laboratory test method that is reliable and can predict the long-term performance of a concrete mix design in a short period of time is not available, a new one may need to be developed.
Task Area 3: Selection, Implementation, and Maintenance of Field Application and Demonstration Projects
Funding is available to states through the ASR Development and Deployment Program for projects focused on applying methods and techniques for ASR prevention and mitigation. Technical assistance for the planning, design, and construction of field projects will be provided. Instrumentation of projects for data collection and analysis will also be provided. Data will be collected, appropriate laboratory testing will be performed, data will be analyzed, and conclusions will be developed on the efficacy of the prevention or mitigation strategy. A goal within the program is to begin field trial implementation by the fall of 2008.
In addition, research will focus on controlled laboratory experiments to seek new or emerging technologies that may be viable and cost effective for ASR mitigation. The mitigation of ASR will be different for bridges and pavements and will take into account the various challenges with mitigating ASR in our transportation structures.
Task Area 4: Assist States in Inventorying Existing Structures for ASR
SAFETEA-LU legislation specifically requires that a system for tracking ASR-affected structures be developed. An evaluation of the current practices that states are using to survey and track ASR-affected bridges, pavements, and other highway structures will be performed. A general plan for including ASR indicators in state bridge inspection programs and pavement survey/pavement management systems will be developed. In addition, it is anticipated that an ASR severity rating system will be developed to assist states in prioritizing mitigation techniques, rehabilitation, or reconstruction.
It is important to distinguish between ASR and other deterioration mechanisms so that the appropriate rehabilitation method is implemented. State engineers have raised concerns with the current methods available for the field detection of ASR. Research will be performed to develop a simple reliable non-destructive field test method that can determine the presence of ASR and predict the total expansion and the rate of expansion.
Task Area 5: Deployment and Technology Transfer of Findings
It is extremely important that information is transmitted in a timely and effective manner to state engineers. The development of an ASR Reference Center is underway. This Center will be housed on FHWA’s website and will contain valuable resources related to ASR. Some of the resources to be included in this Reference Center are research reports; list of reference documents; list of local, national, and international specifications; links to other ASR related websites; and summaries of past field trials for ASR mitigation.
An ASR newsletter called “Reactive Solutions” has been developed. This quarterly newsletter is designed to provide information to state engineers regarding national activities related to ASR, present an environment in which states can learn from each other, and offer a forum for answering questions related to ASR.
Further Information
You can view past issues of the ASR newsletter at http://www.fhwa.dot.gov/pavement/concrete/asr.cfm where you can also find out more information about FHWA’s ASR Development and Deployment Program. If you would like to be added to the distribution list, email [email protected]. If you are interested in participation in a field trial or would like additional information on ASR, please contact Gina Ahlstrom at [email protected].