ACID MAIN DRAINAGE AS A FACTOR OF MICROBIAL INVOLVED CORROSION OF CONCRETE SAMPLES

9th International Multidisciplinary Scientific GeoConference - SGEM2009, www.sgem.org, SGEM2009 Conference Proceedings/ ISBN 10: 954-91818-1-2, June 14-19, 2009, Vol. 2, 439-446 pp

ABSTRACT

Mine activity and acid mine drainage formation is one of the biggest environmental
problems related not only to environment components influence (soil, biosphere, plants
and surface water) but also to man-made materials as concrete degradation because of
its chemical composition and microorganisms’ content. Corrosion associated with
microorganisms has been recognized for over 50 years and yet the study of microbial
involved corrosion is relatively new. Generally, microbial involved corrosion is caused
by the excretion of metabolic intermediates and/or end-products as well as exoenzymes.
Bacteria, cyanobacteria, algae, lichens and fungi, together with protozoa, are all
classified as microorganisms.

The paper is primarily concerned with concrete specimens’ microbial involved
corrosion study under laboratory conditions. In the experiment, sulphate-reducing
bacteria (SRB) genera Desulfovibrio sp. and sulphur-oxidising bacteria
Acidithiobacillus thiooxidans were used. Sulphur oxidizing bacteria Acidithiobacillus
thiooxidans were isolated from the mixed culture obtained from the mine water (the
shaft Pech, the locality Smolnik, Eastern Slovakia). The role of bacteria mentioned
above has been linked to the generation of biogenic sulphuric acid resulting in corrosion
process by dissolution of calcium containing minerals from the concrete matrices.

Microbial involved corrosion of concrete samples proceeded in laboratory reactor by
simultaneous effect of Desulfovibrio desulfuricans as sulphate-reducing bacteria (SRB)
and Acidithiobacillus thiooxidans during 90 days at constant temperature of 25 oC. The
concrete samples were inserted into two media installed in reactor: distilled water as
reference medium and acid mine drainage as real condition approach.

The leachates pH values changes of corroded samples were observed. The penetration
of the corrosion was manifested by structural changes of concrete samples.
Experimental studies confirmed that visible changes of concrete samples surface were
observed. The disruption and the concrete surface changes under sulphuric acid effect
were investigated by scanning electron microscopy (SEM).

Keywords: microbial involved corrosion, SEM, sulphate-reducing bacteria, Acidithiobacillus thiooxidans