Studies on the biodeterioration of concrete by marine algae

Abstract

A variety of materials are used in construction activities and among them, concrete is used very extensively due to inherent advantages. It is proven that various environmental factors impact the long-term performance of a construction material. While the deterioration of concrete due to a variety of causes have been extensively investigated and documented, ?biodeterioration? of construction materials, in general, and the various processes associated with it, have been rather scarcely investigated. In this study, biodeterioration of concrete by marine algae has been experimentally investigated. Two grades of concrete (M20 and M25), two exposure conditions (laboratory and field) were considered for marine algal colonization. Based on a field survey undertaken, three predominant species of marine algae Enteromorpha clathrata (Roth), Ulva fasciata (Delile) and Chaetomorpha antennina (Bory; Kutzing), were identified. The algae were colonized for periods upto 18 months and samples were drawn from the laboratory and field exposure conditions periodically and subjected to (i) sophisticated analytical methods of investigations (SEM, EDAX, XRD, TGA, FTIR, GC-MS); (ii) phycochemical investigations and (iii) macro-level studies (visual examination; non-destructive test-ultrasonic pulse velocity and rebound hammer; compressive strength test). Based on the extensive data obtained through laboratory, field and analytical studies, it is concluded that (i) calcium is utilized for the metabolic activity of marine algae; (ii) various ?fatty acids? released due to the metabolic activity of algae undergo ?oxidative cleavage? and result in a variety of ?dicarboxylic acids? like ?oxalic acid?, ?malonic acid? etc., which chemically react with the strength - imparting complex calcium compounds of concrete and result in end products which lack mechanical strength; (iii) there is deterioration in the quality of concrete, beyond 15 months of exposure, and that about 40-45% of their compressive strength is completely lost at 18 months.