THE DETERMINATION OF THE MOST COMMON CRYSTALLINE ALKALI SILICA REACTION-PRODUCT

Some decades ago, the 'invasion' of European concrete by the alkali-silica reaction (ASR) took a hold in Denmark. Since then, almost every country has had one or more structures damaged by this spectacular kind of concrete corrosion. Till now, little attention has been given to the mineralogy of the crystalline reaction products of the ASR. But in a Belgian petrographic study of the first bridge that had to be demolished because of the damaging effect of an ASR, a detailed research programme was set up. The most common crystalline ASR product could be recognized and isolated. By means of a scanning electron microscope and a semi-quantitative analysing system, an indication of the identity of this globular rosette-like mineral could be found. Combining new data with research results from Canada, Australia and South Africa, a theory could be developed. The globular rosette phase is possibly a still unknown mineral from the rhodesite group.