Alkali silica reaction (ASR) is a pervasive problem in concrete pavement structures in nearly all 50 states in the US. ASR occurs when siliceous aggregate reacts with cement alkali hydroxides within the concrete matrix pores. The reaction creates a gel substance, alkali silica gel, along the aggregate perimeter and within aggregate cracks. The gel absorbs water, expands, and creates tensile stresses within the concrete matrix. The tensile stresses initially are manifested as surface cracking, map cracking, however over time cause large pavement expansion.
As stated in the FHWA Facts Book (March 2013) there are three requirements for the damaging ASR reaction to occur; these are:
1. A sufficient quantity of reactive silica (within aggregates)
2. A sufficient concentration of alkali (primarily from Portland cement)
3. Sufficient moisture
Elimination of any one of these requirements will prevent the occurrence of damaging alkali-silica reaction. Prevention and mitigation of damaging ASR is based upon eliminating or reducing one or more of these three requirements.
New concrete mix requirements for new airfield construction are already specified in Item P-501 of AC 150/5370-104) and UFGS 32 13 11. Risk of ASR is minimized through stringent aggregate testing, limiting the allowed alkalis in the cement, and using supplementary cementitious materials (SCMs) or other additives.
However, many older civilian airfields constructed prior to AC 150/5370-10F (2011) requirements are experiencing large slab expansion resulting in cracking due to ASR. The purpose of this synthesis is to identify the current state of the practice to mitigate ASR-affected pavements at airports.
ASR has been identified at airports worldwide. Practices to retard ASR progression after it has been identified are limited. Approaches range from using sealants to prevent water intrusion all the way to remove and replace. Identification of ASR in pavements has often been described as a death sentence for those pavements.
Airports are looking for measures to take that can mitigate or slow the deleterious effects of ASR and prolong the useful life of the affected pavements. Review of current practices used for mitigating ASR affected airfield pavement sections along with new practices being developed for ASR mitigation would be useful to airports. The report will compile current and emerging ASR mitigation practices, as well as case examples of various mitigation practices for ASR-affected pavements.
The principal investigator will conduct a literature review. The consultant will also develop a list of airports with experience mitigating ASR-damaged pavements. The identified airports should be interviewed to determine the extent of damage, any mitigation performed, the effectiveness of the mitigation, and the approximate unit cost. (Note: A cost-benefit analysis is not required or expected.)
A concise report will be written that summarizes the results of the literature review and interviews. The report will include current practices from the airports studied and emerging practices from the literature review, as well as gaps in knowledge and recommended research.
Partial Information Sources
• Federal Highway Administration (FHWA-HIF-14-004) research report, Methods for Preventing ASR in New Construction: Results of Field Exposure sites, published in 2013.
• IPRF Reports pertaining to ASR (02-5.1, 03-2, 03-9, 03-10, 04-8, 05-7)
• ACRP Synthesis Report 6: Impact of Airport Pavement Deicing Products on Aircraft and Airfield Infrastructure
• Reports of Bi-Annual FHWA ASR Workshops
Mujeeb Basha, Metropolitan Washington Airport Authority
Alessandra Bianchini, U.S. Army Engineer and Development Center
David Brill, Federal Aviation Administration
Greg Cline, Federal Aviation Administration
Nelson Gibson, Transportation Research Board
Ernie Heymsfield, University of Arkansas
Vivek Khana, KSA Engineers, Inc.
Gary Mitchell, American Concrete Pavement Association
Tyson Rupnow, Louisiana Department of Transportation
First meeting: May 17, 2017, Washington, DC
Teleconference: June 9, 2017
Second meeting: November 13, 2017, Washington, DC