16. A Case Study: Bacterial Surface Treatment of Normal and Lightweight Concrete

Bacterial surface treatments for concrete have become increasingly popular due to their strong potential to improve the durability of concrete structures for practical usage. Compared to bacteria inoculated into the cement matrix, it is easier to provide the proper environment for bacteria when the bacteria are applied onto the surface of the concrete. Moreover, the bacterial surface treatment method has a number of advantages in comparison with conventional surface treatment methods using polymer-based coating materials, including water repellents or pore-blockers. Three advantages are as follows: (1) a similar thermal expansion property between the microbially precipitated calcium carbonate and the concrete surface, (2) environmentally friendly characteristics, and (3) the potential for self-healing. A surface treatment, especially for lightweight concrete, is very important to ensure good durability, as the durability of lightweight concrete is generally lower than that of normal concrete. In the present chapter, a previous work of the authors, a study of the bacterial surface treatment of normal and lightweight concrete (Kim et al. 2013) is reviewed and summarized. The surfaces of normal and lightweight concrete specimens were treated with a liquid medium containing bacteria. Macro- and micrographic assessments were done to analyze the shapes and distribution of the calcium carbonate crystals. The capillary water absorption of the concrete specimens was measured to evaluate the effects of the bacterial precipitation of calcium carbonate on the moisture transport properties, as these properties were thought to affect the durability of the concrete.