The Thaumasite Form of Sulfate Attack in Concretes Containing a Source of Carbonate Ions--a Microstructural Overview

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Title: The Thaumasite Form of Sulfate Attack in Concretes Containing a Source of Carbonate Ions--a Microstructural Overview

Author(s): N. J. Crammond and M. A. Halliwell

Publication: Special Publication

Volume: 154

Issue:

Appears on pages(s): 357-380

Keywords: calcite; carbonates; concretes; dolomite; foundations;

Date: 5/1/1995

Abstract:
Over the last 50 years, many researchers have investigated the subject of sulfate attack of concrete and special cements have been formulated to combat the problem. However, recent site investigative work and laboratory- based studies carried out by the Building Research Establishment have shown that a particular form of sulfate attack can proceed even in some concretes which were specifically designed to provide good sulfate resistance. In this type of attack, the main mechanism of deterioration is the breakdown of the calcium silicate hydrate phases in the hardened cement paste in the presence of an available supply of sulfate and carbonate ions to produce the mineral thaumasite (CaSiO3CaSO4CaCO315H2O). A microstructural overview incorporating three examples of the thaumasite form of sulfate attack is presented in this paper. The combination of optical and electron microscopy has proved to be a very powerful technique for examining the processes of deterioration in carefully selected site samples