Field Survey of Delayed Ettringite Formation-Related Damage in Concrete Bridges in the State of Maryland

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Title: Field Survey of Delayed Ettringite Formation-Related Damage in Concrete Bridges in the State of Maryland

Author(s): R.A. Livingston, C. Ormsby, A.M. Amde, M.S. Ceary, N. McMorris, and P.G. Finnerty

Publication: Special Publication

Volume: 234

Issue:

Appears on pages(s): 251-268

Keywords: alkali-silica reaction (ASR); concrete; ettringite; impact echo; Pontis; potassium autoradiography; SEM

Date: 3/22/2006

Abstract:
In order to evaluate the distribution of damage related to delayed ettringite formation (DEF) in Maryland bridges, a pilot field study was carried out using both destructive and nondestructive test methods. A sampling design was developed based on the Maryland Bridge Inventory. This was screened for bridges with ratings of 4 or 5 and the term “wet map cracks” in the inspection reports. A sample of 16 bridges was selected to give a uniform geographical distribution across the Maryland State Bridge districts. At each bridge several cores were drilled for subsequent examination of fracture surfaces by Scanning Electron Microscope (SEM) with energy dispersive X-ray fluorescence. At every bridge, ettringite was detected, but alkali-silica reaction (ASR) gel was detected only very rarely. In more heavily damaged locations, the occurrence of ettringite crystals was more frequent, appearing in the rims around aggregates as well as in voids. Also, the morphology of the ettringite crystals appeared to be more lamellar than acicular. The implications are that: DEF is widespread geographically, map cracking is not diagnostic only for ASR, and the onset of DEF may be associated with a change in ettringite crystal morphology.