The following is an excerpt From a Concrete Expert Witness Petrographic Investigation Report:

 

The investigation was reconnaissance in nature and involved

the completion of microscopical examinations in reflected

and transmitted light. A thorough analysis of the concrete via

petrographic methods requires the extraction of concrete core

samples or other samples representative of the concrete in

the field, and their examination via procedures described in

ASTM C 856 [Image 1 at right].

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The samples were visually inspected and photographed in

their as-received condition. The analysis consisted of a

reconnaissance examination of the materials in reflected and

transmitted light. No surfaces were prepared by lapping,

grinding, or thin section preparation, to expedite the analysis.

As-received and fresh fracture surfaces were examined via a

stereomicroscope with 3-180x magnification capability. Grain mounts were prepared using immersion oils with known refractive indices and then examined with a petrographic microscope with 50-500x magnification capability.

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The aggregate sample was opaline shale. Figure 2 shows examples of the rock. Opaline shale has the potential for high reactivity in terms of ASR.
The popout from the sealed concrete surface contained an abundance of ASR gel. A fragment of opaline shale was observed at the base of the popout. The popout detached across laminations in the shale. Figure 3 shows examples of the popout and evidence of ASR.
The popout from the hard-trowel finished surface also contained ASR gel. A fragment of opaline shale was observed at the base of the popout. The popout detached along a lamination in the shale. Figure 4 shows examples of the popout and evidence of ASR.
Based on the observations and findings described above, all of the samples presented evidence of the presence of reactive components. The popouts are most likely due to ASR.

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