Quantifying microbially induced deterioration of concrete: initial studies

Microbially induced concrete corrosion damages concrete structures, especially sewage collection systems, throughout the world, costing municipalities millions of dollars worldwide. The overall theory explaining microbial deterioration of concrete is quite well developed in the literature. There is, however, very little information of a quantitative nature that can be used to model the process. This manuscript presents a review of the current literature, shares the initial results of studies designed to quantify and model the process, and makes some suggestions of further areas of research needed to advance modeling of the process. Initial results have revealed that widely varying numbers of acidophilic sulfur-oxidizing microorganisms (ASOM) and neutrophilic sulfur-oxidizing microorganisms (NSOM) are present in the sewage inoculum. Numbers as high as 106 MPN/100ml and as low as non-detectable have been found in sewage. A small number, 0.12 (MPN/cm2)/(MPN/100 ml) ASOM and 0.04 (MPN/cm2)/(MPN/100 ml) NSOM are able to attach to initially weathered concrete and then even smaller numbers of these, 1% ASOM and 3% NSOM, survive to colonize and further reduce the pH of the concrete. These set up the microbial succession required for the full development of the concrete deterioration process. More data quantifying the environmental conditions that effect the numbers of SOM in sewage and their survival on concrete is required before an accurate model of the entire deterioration process can be developed.