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

Abstract

During their metabolism, the microorganisms can produce acids able to induce the degradation of cement. Two acidifying but alkalophilic fungal strains have been isolated from a soil sample. One is an Aspergillus strain which produces gluconic and oxalic acids. These acids induce (after eleven months of contact) a dissolution of portlandite (with a low leaching of calcium), an increase in the cement porosity (+ 11.4 %), a loss of the bending strength (— 78 %). The second strain, a Mycelia sterila produces gluconic and malic acids, responsible (during the same period) for a very important dissolution of portlandice (with a leaching of calcium : 4.2 % of the initial content), an increase in the porosity (+ 11 % also), and a loss of the bending strength less important than in the other case (— 62 %). The direct contact of mycelia with the cement does not increase the effects of the acids. A low pH and a high temperature favour the acids production.