An applied mineralogical investigation of concrete degradation in a major concrete road bridge

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Authors:MacLeod, G.; Hall, A. J.; Fallick, A. E.
Author Affiliations:Primary:
Univ. Glasgow, Dep. Geol. and Appl. Geol., Glasgow, United Kingdom
Other:
Scott. Univ. Res. and React. Cent., United Kingdom
Volume Title:Mineralogical Magazine
Source:Mineralogical Magazine, 54 Part 4(377), p.637-644. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0026-461X
Publication Date:1990
Note:In English. 17 refs.; illus. incl. 1 table, sect.
Summary:A core of concrete taken from a major road bridge in the Strathclyde Region, Scotland, has been subjected to an applied mineralogical investigation, which involved stable isotope analysis, petrography, X-ray diffraction and scanning electron microscopy. The structure is actively undergoing severe degradation due to mineral growth which is related to chemical reactions between the concrete and pore fluid. The physical growth of minerals causes disfigurement and structural weakening. Pyrite and pyrrhotine hosted by dolerite aggregate appear to have been oxidized, providing sulphate for the deposition of ettringite and minor gypsum, in spheroidal cavities within the cement paste. The rainwater which passes through the structure mobilising sulphate from original gypsum in the paste and oxidizing the iron sulphides is also involved in the further leaching of elements from the cement paste and in the deposition of calcite. The isotopic values of calcites forming a crust on the concrete and a stalactite under the bridge are similar with δ13C= -19 ppm PDB and δ18 ppm= +16 ppm SMOW. We suggest that atmospheric carbon dioxide was the carbon source. The carbon isotopic fractionation of -12 ppm from atmospheric carbon dioxide of δ13C= -7 ppm, (O'Neil and Barnes, 1971) can best be explained as due to a kinetic fractionation related to the hyper-basicity of the pore water. The equilibrium formation temperature of about 45°C calculated from the oxygen isotope values and assuming a δ18O value of meteoric water of -8 ppm SMOW, is considered unreasonable. The exceptionally low δ18O values are attributed mainly to reaction kinetics and the calcite inheriting its oxygen, two-thirds from atmospheric carbon dioxide and one third from the meteoric formation water (O'Neil and Barnes, 1971). A δ18O value of atmospheric carbon dioxide of +41 ppm SMOW and a δ18O value of meteoric water of -8 ppm SMOW, lead to a calculated δ18O value for the calcites of +10 ppm SMOW. The calcites analysed have a value of +16 ppm and this may be due to partial re-equilibration towards a calculated value of +21 ppm for calcite in equilibrium with the meteoric water at 20°C.
Subjects:Bridges; Concrete; Construction materials; Degradation; Engineering geology; Laboratory studies; Mineral composition; Europe; Great Britain; Scotland; United Kingdom; Western Europe; Materials, properties; Strathclyde
Abstract Numbers:91M/1561
Record ID:1992002296
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland
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