MICROSCOPY AND COMPUTED MICRO-TOMOGRAPHY FOR EVALUATION OF MICROBIAL SELF-HEALING IN CONCRETE
Author(s): Wang, J., Tittelboom, K. van and De Belie, N.
Paper category: Conference
Book title: XIII International Conference on Durability of Building Materials and Components - XIII DBMC
Editor(s): Marco Quattrone, Vanderley M. John
Print ISBN: none
Publication year: 2015
Total Pages: 8
Abstract: Autonomous self-healing of materials, implies that the material is adapted in such a way that damage is repaired automatically. To obtain self-healing in concrete, several smart mechanisms can be introduced, such as activators or fibres to stimulate autogenous healing, encapsulated (pre)polymers or bacteria. The technology of microbial self-healing makes use of bacteria that promote the precipitation of calcium carbonate when they make contact with the appropriate nutrients and water. In order to survive the high alkalinity in the concrete matrix and the reducing pore sizes due to the ongoing cement hydration, bacterial cells or spores are applied, protected by a carrier material or encapsulation system. Crack formation in the concrete acts hereby as a trigger to break the capsules and activate the bacteria. The precipitated bacterial calcium carbonate will fill the crack and restore the water tightness of the concrete element.
The most obvious technique to evaluate the self-healing efficiency is a visual examination of the crack filling. Optical microscopy allows to evaluate crack filling at the concrete surface, whereas computed micro-tomography also allows to visualize the complete crack internally in a non-destructive way. The current study gives an overview of crack healing ratios and maximum healed crack widths for various microbial based self-healing strategies. Incorporation of Bacillus sphaericus cells, protected by diatomaceous earth, allowed healing of 0.17 mm wide cracks in mortar specimens in 40 days time. B. sphaericus spores, protected by melamine based microcapsules, were able to heal cracks of almost 1 mm in three weeks time. Encapsulation of spores in hydrogels resulted in healing of 0.5 mm cracks within one week. Computed micro-tomography enabled quantification of the amount of deposited calcium carbonate. Also crack filling by polymeric carrier materials for bacteria, such as polyurethane, could be evaluated with this technique.
Online publication: 2015
Publication Type: full_text
Public price (Euros): 0.00