Degradation modelling of concrete submitted to sulfuric acid attack

Bio-deterioration of concrete, which is very common in sewer system and waste water treatment plant, results in significant structure degradation. Normally, the process can be described by the two following steps: Biochemical reactions producing biogenic aggressive species (H₂SO₄ is one of the most significant biogenic acid in sewer pipes), and chemical reactions between biogenic aggressive species and cement hydration products which is responsible for concrete degradation. A reactive transport model is proposed to simulate the chemical degradation process of cementitious materials in contact with H₂SO₄ solution. The dissolution of portlandite (CH) and calcium silicate hydrates (C–S–H) and the precipitation of gypsum (p) are described by mass action law and threshold of ion activity products. To take into account the continuous decrease of the Ca/Si ratio during the dissolution of C–S–H a generalization of the mass action law is applied. A simplified damage model is introduced to characterize the degradation of concrete due to the swelling of gypsum. Some experiments reported in literature are simulated. The numerical results and the experimental observations are compared and discussed.