Novel bacteria-based self-healing concrete (single capsule approach)

• Main Author: Siti Umairah Abd Rahman
• Other Authors: En-Hua Yang
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Civil engineering
• Online Access: https://hdl.handle.net/10356/158783
• Institution: Nanyang Technological University

Cracking in concrete poses a serious threat to the structural integrity of the structure. The existing manual repair methods are labour-intensive, costly and inconvenient hence the emphasis for a more sustainable method to manage the cracks. Microbial self-healing agents are an increasingly sought-after alternative to enable self-healing of the cracks. The high alkalinity in concrete presents a challenge for the survival of the bacteria, thus encapsulation is needed to protect it. Out of the myriad of encapsulation methods, Reactive Magnesia Cement (RMC) which is a low alkalinity cementitious material is a highly regarded candidate for this encapsulation. Nutrients are needed to supplement the bacteria for self-healing, primarily Yeast Extract (Ye) and Calcium Lactate (CaL). When added to the matrix, nutrients pose a threat to its mechanical performance. Therefore, this Final Year Report investigates the feasibility of using RMC, that has undergone accelerated carbonation, as the encapsulation material for both the bacteria (Bacillus Cohnii) and nutrients in a Single Capsule (RMC-B-N) to achieve self-healing without compromising the mechanical properties of the matrix. Crack width measurements, water permeability test and ultrasonic pulse velocity (UPV) test were conducted to establish the self-healing feasibility. Compressive strength test, flowability test and setting time test were done to assess the influence on the fresh and hardened properties of the matrix. Also, SEM and XRD tests were conducted to observe the microstructure and morphology of the capsule. A gradient density characteristic of the capsule is observed, with its dense surface covered with Hydrated Magnesium Carbonates (HMCs) and its porous core region of brucite. Key results from the addition of RMC-B-N capsule reported complete crack healing for cracks between 200μm to 400μm and significant healing for bigger cracks of 500μm. Also, a 9.5% increase in compressive strength was observed. Additionally, a novel idea of a PC-based encapsulation of Nutrients (PC-N), whilst maintaining the RMC based encapsulation for the bacteria (RMC-B) was explored. This project found that the compressive strength upon addition of PC-N and RMC-B was greatly reduced, which reasons the need for RMC under accelerated carbonation to create the gradient characteristic of the capsule for better encapsulation.