Biodeterioration and Chemical Corrosion of Concrete in the Marine Environment: Too Complex for Prediction

Abstract

Concrete is the most utilized construction material worldwide. In the marine environment, it is subject to chemical degradation through reactions with chloride (the most important ion), and sulfate and magnesium ions in seawater, and to biodeterioration resulting from biological (initially microbiological) activities, principally acid production. These two types of corrosions are reviewed and the failure of attempts to predict the degree of deterioration resulting from each is noted. Chemical (abiotic) corrosion is greatest in the splash zone of coastal constructions, while phenomenological evidence suggests that biodeterioration is greatest in tidal zones. There have been no comparative experiments to determine the rates and types of microbial biofilm formation in these zones. Both chemical and microbiological concrete deteriorations are complex and have not been successfully modeled. The interaction between abiotic corrosion and biofilm formation is considered. EPS can maintain surface hydration, potentially reducing abiotic corrosion. The early marine biofilm contains relatively specific bacterial colonizers, including cyanobacteria and proteobacteria; these change over time, producing a generic concrete biofilm, but the adhesion of microorganisms to concrete in the oceans has been little investigated. The colonization of artificial reefs is briefly discussed. Concrete appears to be a relatively prescriptive substrate, with modifications necessary to increase colonization for the required goal of increasing biological diversity.

Keywords: biofilm; colonization; degradation; extracellular polymeric materials (EPS); intertidal and splash zones; microorganisms; subtidal.

Figure 1

Concrete docks for artisanal fishing boats in Campeche, southern Mexico. Note that areas reached only by the marine spray appear devoid of (visible) microbial colonization, whereas intermittently submerged surfaces are covered by black biofilms. Permanently submerged areas are heavily covered by phototrophic communities. San Francisco de Campeche, Campeche, Mexico.

Figure 2

Intertidal concrete structures such as the base of this fisherman’s house, built over a rocky shore, exhibit a heterogeneous coverage of microorganisms. Lerma village, Campeche, Mexico.

Figure 3

Biofilms covering concrete surfaces often exhibit a black phenotype, indicating the likely presence of scytonemin-producing cyanobacteria as a functional adaptation for water stress and excessive insolation. San Francisco de Campeche city, Campeche, Mexico.