Clay mineral characterization through the methylene blue test: comparison with other experimental techniques and applications of the method

Abstract

This article illustrates an experimental study of clay mineral characterization conducted with the aid of the methylene blue "stain" test, which yields a semiquantitative evaluation of the activity of a geomaterial based on the type and quantity of clay minerals contained in it. The properties of clay minerals are described briefly, with special regard to their swelling behaviour in the presence of water. The testing method is described with reference to the procedures and interpretation criteria specified in the Association française de Normalization (AFNOR) and American Society for Testing and Materials (ASTM) standards. The results are then presented of a testing campaign conducted to assess the applicability of the methylene blue test for the characterization of geomaterials through a comparison with other testing methods. Additional tests were performed on stratigraphic sequences to identify the levels containing higher proportions of active clay minerals, based on their tendency to swell on coming into contact with water. This characterization technique was applied to marly–arenaceous formations of the Langhe region (Piedmont, Italy), where planar sliding instability phenomena have often been observed following abundant rainfall, and marly–arenaceous formations of Monferrato (another region in southeast Piedmont, Italy), where studies of a geological–structural nature have often revealed traces of postsedimentary tectonic phenomena.Key words: methylene blue stain test, marl, clay mineral, swelling phenomenon, planar sliding instability.