Location
University of Leeds, UK
Event Website
https://engineering.leeds.ac.uk/icdcs2018
Keywords
ASR, ACR, Fine-grained dolomitic limestone, Cryptocrystalline quartz, PLM, SEM-EDS
Abstract
The root cause of distress in two different concrete structures made from carbonate coarse aggregates that fit the textural and compositional criteria cited for ACR was found to be caused by ASR, not ACR. Stereo-optical examination and transmitted polarized light microscopy (PLM) analysis showed that the concretes contain some dark gray, fine-grained argillaceous dolomitic coarse aggregates in which secondary white deposit filling the cracks extending from these aggregates into the paste (as well as lining air voids) is ASR gel. Back scattered electron (BSE) imaging with EDS spectra and x-ray elemental mappings, clearly confirm that the white secondary deposits consist of ASR gel. BSE images with EDS spectra and X-ray maps of different samples for each element within areas occupied by the gel showed typical ASR gel. High magnification PLM examination showed the presence of cryptocrystalline to microcrystalline quartz in pockets in the matrix of the rock. The presence of Si-rich phases as finely divided interstitial cryptocrystalline silica minerals intermixed with the matrix and locally in pockets in the matrix of the rocks is confirmed by X-ray mapping, and these silica minerals are the source of silica for ASR. The uniform Mg concentration as reflected by the scan across the dolomite rhombs indicates no sign of dedolomitization, and there was no evidence of brucite formation. While the aggregates have the classic texture often cited for ACR, there is no evidence of the deterioration of the dolomite rhombs or migration of Mg into the rims/peripheries of the dolomite rhombs. Instead, in these cases there is compelling evidence that the concrete distress was caused by ASR and not ACR.
Streaming Media
Included in
Civil Engineering Commons, Engineering Science and Materials Commons, Materials Science and Engineering Commons
Alkali Reactive Carbonate Rocks: Is it Alkali Silica Reaction (ASR) or Alkali Carbonate Reaction (ACR)?
University of Leeds, UK
The root cause of distress in two different concrete structures made from carbonate coarse aggregates that fit the textural and compositional criteria cited for ACR was found to be caused by ASR, not ACR. Stereo-optical examination and transmitted polarized light microscopy (PLM) analysis showed that the concretes contain some dark gray, fine-grained argillaceous dolomitic coarse aggregates in which secondary white deposit filling the cracks extending from these aggregates into the paste (as well as lining air voids) is ASR gel. Back scattered electron (BSE) imaging with EDS spectra and x-ray elemental mappings, clearly confirm that the white secondary deposits consist of ASR gel. BSE images with EDS spectra and X-ray maps of different samples for each element within areas occupied by the gel showed typical ASR gel. High magnification PLM examination showed the presence of cryptocrystalline to microcrystalline quartz in pockets in the matrix of the rock. The presence of Si-rich phases as finely divided interstitial cryptocrystalline silica minerals intermixed with the matrix and locally in pockets in the matrix of the rocks is confirmed by X-ray mapping, and these silica minerals are the source of silica for ASR. The uniform Mg concentration as reflected by the scan across the dolomite rhombs indicates no sign of dedolomitization, and there was no evidence of brucite formation. While the aggregates have the classic texture often cited for ACR, there is no evidence of the deterioration of the dolomite rhombs or migration of Mg into the rims/peripheries of the dolomite rhombs. Instead, in these cases there is compelling evidence that the concrete distress was caused by ASR and not ACR.
https://docs.lib.purdue.edu/icdcs/2018/icc/26
