Evaluation of cement degradation induced by the metabolic products of two fungal strains

Summary During their metabolism, microorganisms can produce acids able to bring about the degradation of cement. Two acid-producing alkalophilic fungal strains have been isolated from soil, a strain ofAspergillus niger which produces gluconic and oxalic acid and ofMycelia sterila which produces gluconic and malic acid. After eleven months of contact the acids produced byAspergillus dissolved portlandite with a low leaching of calcium, increased the cement porosity by 11.4%, and reduced the bending strength by 78%. The second strain is responsible for a significant dissolution of portlandite with a leaching of calcium of 4.2% of the initial content, an increase of the porosity of 11%, and a loss of the bending strength of 62%. Direct contact of mycelia with the cement surface is not necessary for effective dissolution to take place. Low pH and a high temperature favor the the production of acids.