Crack healing in reactive MgO-slag system via bacteria induced carbonate precipitation

• Main Author: Zheng, Yanying
• Other Authors: Qian Shunzhi
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Civil engineering
• Online Access: https://hdl.handle.net/10356/150719
• Institution: Nanyang Technological University

In the Concrete industry, the most widely used binding ingredient for concrete, portland cement (PC), is accountable for around 8% of global anthropogenic carbon dioxide (CO2) emissions. Reactive magnesium oxide (MgO) cement has been regarded as a promising alternative binding material for concrete production. It gains strength through carbonation curing, which results in lesser net CO2 emissions as compared to PC. Ground granulated blast-furnace slag (GGBS), which is a type of supplementary cementitious materials (SCM), has also been employed in MgO mixes to reduce carbon footprint. Prevalence of cracks in concrete is a common issue and to prevent the expansion of them, proper and immediate treatment should be done. Traditional fixing methods such as cement grouting and maintenance are challenging and costly. Hence, it is more advisable and economical to prevent the formation of early age small cracks to larger width. To overcome these situations, self-healing concrete techniques via microbial approach are adopted. Biologic and self-healing concrete has become a promising solution, and regarded as cost effective and environmentally friendly possibly due to it being pollution free and natural for concrete repair. In this study, crack healing in reactive MgO-slag system was investigated via bacteria induced carbonate precipitation. Self-healing regimes such as alternating bacteria medium soaking and carbon dioxide curing cycles and alternating water and carbon dioxide cycles were adopted in this project. To characterise the healing effect, crack width measurement, resonant frequency test, sorptivity test and tensile test were conducted. It was found that bacteria had the ability to precipitate carbonates, which filled small cracks, stiffened the concrete, and reduced the permeability of damaged concrete.