- Magnel Laboratory for Concrete Research, Department of Structural Engineering, Ghent University
- Title of PhD dissertation:
- Self-healing Concrete by Means of Immobilized Carbonate Precipitating Bacteria
- Promoter: Prof. dr. ir. Nele De Belie, Magnel Laboratory for Concrete Research, Department of Structural Engineering
- Co-promoter: Prof. dr. ir. Willy Verstraete, Laboratory for Microbial Ecology and Technology, Department of Biochemical and Microbial Technology
- Self-healing concrete is regarded as a promising solution to reduce the high maintenance and repair cost of concrete infrastructure. Due to the limited autogenous healing capacity of concrete itself, additives are needed to enhance the self-healing properties. These healing agents are pre-added into the concrete during mixing or casting and are expected to play their role (heal cracks) when cracking occurs. This PhD work aims to explore a microbial-based self-healing strategy for concrete, which has the distinct features of environmental friendliness, long-term viability and low cost. Carbonate precipitating bacteria were added into mortar specimens to in-situ heal concrete cracks when cracking occurred. Bacillus sphaericus, an alkaline spore-forming ureolytic strain, was selected as the microbial source due to its high carbonate production capacity, alkaline adaptability and long-term viability. Four types of carriers were investigated in this study. In view of the self-healing efficiency and the possibility for practical use, the most promising carriers are microcapsules and superabsorbent polymers. Overall, this doctoral research demonstrated the feasibility of using immobilized carbonate precipitating bacteria for self-healing concrete. The novel carriers used opens the perspective to bring self-healing concrete into practice.
- Date of defense: March 4, 2013
- Laboratory of Microbial Ecology and Technology, Department of Biochemical and Microbial Technology, Ghent University
- Title of PhD dissertation:
- Housing Methane-Oxidizing Bacteria on building materials for air bioremediation and bioprecipitation
- Promoter: Prof. Dr. Ir. Nico Boon, Laboratory for Microbial Ecology and Technology, Department of Biochemical and Microbial Technology
- Co-promoter: Dr. ir. Adrian Ho, Department of Microbial Ecology, Netherlands Institute of Ecology (NIOO-KNAW)
- Methane is one of the most important greenhouse gasses after carbon dioxide and its concentration in the atmosphere has increased exponentially for the past century. High methane emission can be found in places such as cities and animal barns. Methane-Oxidizing Bacteria (MOB) is a unique group of bacteria capable of oxidizing methane. Building material is a potential niche to immobilize the bacteria to remediate methane in places with a high methane emission The PhD work aims to explore the capacity of MOB to remediate methane in places with high methane emission. Concomitantly, the bacterial capacity to protect the building material by means of calcium carbonate surface biodeposition was also investigated. Based on kinetic studies, Methylocystis parvus OBBP was selected as the tested strain as it exhibited high activity to remove atmospheric methane at concentration level similar to animal barns when immobilized on building materials. Both in lab scale and field test, the bacteria could remove methane in a biofilter setup using Autoclaved Aerated Concrete (AAC) as the carrier materials. Additionally, M. parvus could induce calcium carbonate precipitation on AAC surface and as a result lowered water penetration rate as a concrete dissolution factor to the material. This in turn would conserve the material. Overall, the doctoral research has demonstrated the capacity of MOB to remediate methane and protect building material when immobilized on the material. In view of the capacity to induce calcium carbonate precipitation, a more sustainable microbial process is given compared to the currently applied urea hydrolysis pathway.
- Proposed date of defense: March 31, 2015
- Laboratory of Mechanics of Materials and Constructions (MeMC), Free University of Brussels (VUB)
- Title of PhD dissertation:
- Experimental assessment of fracture and autonomous healing of concrete and polymer systems
- Promoter: Prof.Dr.ir. Danny Van Hemelrijck, Laboratory of Mechanics of Materials and Constructions (MeMC), Free University of Brussels (VUB)
- Co-promoter: Prof.Dr.ir. Dimitrios Aggelis, Laboratory of Mechanics of Materials and Constructions (MeMC), Free University of Brussels (VUB)
- The use of materials which have autonomous self-healing capabilities will extend the operational life of structural components with at least 20 years and as such contribute towards building more sustainable world. In the present study, concrete and polymer systems were provided with self-healing capabilities by embedding small capsules containing healing agents. When cracking occurs these capsules will break and the healing agent will leak into the crack opening and consequently seal and restore the mechanical performance of the material. Until present simplified fracture tests (like TDCB tests) are used to evaluate the healing performance. However, detailed analysis proofed that these tests yielded controversial data which prevented accurate comparison of the obtained healing phenomena. This research critically reviews and investigates in depth other potential test configurations. New test setups in combination with advanced optical and acoustic methods like Digital Image Correlation, Acoustic Emission, Ultrasound Sensing and Microscopy were used to monitor and assess the healing efficiency as well as the circumstances under which damage and subsequent healing occurs. Classical fracture theories were applied to characterise crack nucleation, growth, closure and crack reopening upon reloading. For the first time, the contribution of embedded capsules on the material toughness is quantified. Additionally, new parameters were defined for computing healing efficiency. The thesis dealing with the first generation of healing polymer and concrete systems aims to pave the way towards future self-healing real-life applications.
- Date of public defense: March 19, 2015.