Biodeterioration of Concrete Sewer Pipes: State of the Art and Research Needs

Biodeterioration of concrete sewers is a common problem that results in concrete disintegration and significant damage. Two stages are normally identifiable in the process: an initiation stage, during which the concrete pore water pH is reduced from an initial value of over 12 to a value of about 9 by ingress of hydrogen sulfide gas and carbon dioxide (carbonation) and subsequent reaction with the hydrated cement paste; and a second stage, active biodeterioration, during which microorganisms excrete sulfuric acid that attacks the hydrated cement paste (HCP). Various national codes and standards provide some guidance to mitigate this problem. Sulfur-oxidizing microorganisms growing on the sewer walls have been isolated as the main culprit, but other phenomena come into play before biodeterioration occurs. Steady-state biodeterioration rates of 3 mm/year have been proposed in the literature. A detailed literature review was conducted to evaluate the various aspects of concrete biodeterioration and determine further research needs. This state-of-the-art report summarizes the deterioration mechanisms involved in biodeterioration of concrete sewers and the work necessary to complete the modeling of this phenomenon. A conceptual model of the processes is presented. (C) 2011 American Society of Civil Engineers.