U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
|Accelerating Infrastructure Innovations|
Publication Number: FHWA-HRT-07-016
Date: August 2007
The Federal Highway Administration (FHWA) has released an updated resource for transportation practitioners that provides guidance on using hydraulic cement concrete (HCC) petrography. Petrographic Methods of Examining Hardened Concrete: A Petrographic Manual (Pub. No. FHWA-HRT-04-150), complete with procedures, instructions, and photographs, is designed to aid practitioners who lack formal petrographic training. Petrographic analysis uses microscopic techniques to study concrete condition and quality, as well as distress, deterioration, and failure. "The manual highlights methods that have proven to be the most useful in the field and in the laboratory," says Richard Meininger of FHWA's Office of Infrastructure Research and Development.
The manual discusses the petrography of HCC, chemical reactions of rocks and minerals in HCC, and the identification of common rocks and minerals necessary for a complete description of HCC. The targeted audience includes petrographers, geologists, engineers, chemists, consultants, and university researchers. "The manual will be helpful in doing forensic work and troubleshooting problems related to concrete deterioration, as well as examining mineral aggregates or recycled aggregates," says Meininger. For example, if concrete shows cracking soon after construction, a petrographic analysis can help determine the nature of the cracking and its possible cause. Currently many of the practitioners performing concrete petrography work are geologists with formal training in optical mineralogy and petrography. Because the petrographic examination of HCC is more qualitative than quantitative, it can be difficult to train new practitioners who lack the field experience in examining HCC and identifying the various features that may indicate the quality of the material. The manual aims to close this gap.
Developed in 1992 by petrographer Hollis N. Walker of the Virginia Transportation Research Council (VTRC), the original manual has served as an important guide to the field of concrete petrology. D. Stephen Lane, senior research scientist at the VTRC, has led the effort to update the publication to reflect recent advances in techniques and work in the field. Additions include chapters on the use of the scanning electron microscope to examine concrete and concrete-making materials and the identification and classification of rocks and minerals in aggregates. Another useful addition is a chapter on alkali-aggregate reactions, which outlines the process for investigating a case of concrete deterioration and illustrates the features that provide evidence of alkali-silica or alkali-carbonate reactions.
With the new chapter on alkali-aggregate reactions, the updated manual will serve as a vital tool for FHWA's alkali-silica reactivity (ASR) program, which is aimed at preventing and mitigating ASR in concrete pavements and structures (see April 2007 Focus). "The Petrographic Manual will help achieve one of the objectives in the inventory of structures affected by ASR by confirming that the deterioration mechanism is actually ASR and not some other type of deterioration, and will also help in recognizing situations where other deterioration mechanisms may be occurring in conjunction with ASR," says Meininger. "In some cases, the question may be asked: 'Which deterioration occurred first, and was it a causal factor in subsequent deterioration?'"
The manual is available online at www.fhwa.dot.gov/pavement/pccp/pubs/04150. For more information, contact Richard Meininger at FHWA, 202-493-3191 (email: firstname.lastname@example.org).
Above: Senior Research Scientist D. Stephen Lane in the Virginia Transportation Research Council's Petrography Laboratory in Charlottesville, VA.
Left: Partially automated linear traverse equipment for determining air-void parameters.