Abstract
Identification of thaumasite (CaSiO 3·CaO 3·CaSO 4·15H 2O) in concrete undergoing external sulfate attack by X-ray powder diffraction or by microscopic techniques is difficult due to its crystallographic and morphological similarity with ettringite. Widefield Raman chemical imaging via liquid crystal tunable filter (LCTF) technology has been used in a preliminary study to determine the presence of thaumasite in association with ettringite (3CaO·Al 2O 3·3CaSO 4·32H 2O) and gypsum (CaSO 4·2H 2O). Raman chemical imaging combines Raman spectroscopy with optical microscopy and digital imaging to provide images with molecular-based contrast. Thaumasite has three major peaks at 658, 990, 1076 cm −1 and three minor peaks at 417, 453, 479 cm −1. Ettringite has major peaks at 990, 1088 cm −1. Gypsum has a major peak at 1009 cm −1 and minor peaks at 417, 496, 621, 673, 1137 cm −1. When these minerals are presented together, Raman chemical imaging provides an excellent way to determine their molecular composition and spatial distribution within the sample.
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