Evaluation of Microencapsulation Techniques for MICP Bacterial Spores Applied in Self-Healing Concrete

Abstract

Concrete cracks must be repaired promptly in order to prevent structural damage and to prolong the structural life of the building (or other such construction). Biological self-healing concrete is a recent alternative technology involving the biochemical reaction of microbial induced calcium carbonate precipitation (MICP). This study determined the most appropriate technique to encapsulate spores of Bacillus sphaericus LMG 22257 with sodium alginate so as to protect the bacterial spores during the concrete mixing and hardening period. Three techniques (extrusion, spray drying and freeze drying) to encapsulate the bacterial spores with sodium alginate were evaluated. The freeze-drying process provided the highest bacterial spore survival rate (100%), while the extruded and spray-dried processes had a lower spore survival rate of 93.8% and 79.9%, respectively. To investigate the viability of microencapsulated spores after being mixed with mortar, the decomposed urea analysis was conducted. The results revealed that the freeze-dried spores also showed the highest level of urea decomposition (metabolic activity assay used as a surrogate marker of spore germination and vegetative cell viability). Thus, the self-healing performance of concrete mixed with freeze-dried spores was evaluated. The results showed that the crack healing ratio observed from the mortar specimens with freeze-dried microencapsulated spores were significantly higher than those without bacteria. This study revealed that freeze drying has a high potential as a microencapsulation technique for application to self-healing concrete technology.

Microbe‐Mediated Extracellular and Intracellular Mineralization: Environmental, Industrial, and Biotechnological Applications

“…[ 296 ] Current research focuses on the use of microencapsulation techniques for protecting bacteria and bacteria spores that are incorporated in concretes designed for self‐healing over lengthy periods. [ 297,298 ]…”

On the Applicability of a Precursor Derived from Organic Waste Streams for Bacteria-Based Self-Healing Concrete

“…Cracks closure reduce the ingress of water and harmful agents (i.e., chlorides) and, therefore, it is expected to improve the durability of concrete. Several methodologies have been proposed in the current literature to improve the self-healing capacity of concrete, such as incorporating fibers (Li et al, 1998;Yang et al, 2009), superabsorbent polymers (Kim and Schlangen, 2011;Snoeck et al, 2016) and encapsulated healing agents (Van Tittelboom et al, 2011;Wiktor and Jonkers, 2011;Wang et al, 2014a;Wang et al, 2014b;Mors and Jonkers, 2017a;Mors and Jonkers, 2017b;Palin et al, 2017;Wang et al, 2018;Pungrasmi et al, 2019;Xu et al, 2019). One of the first studies on the applicability of the latter technology was conducted by Mors and Jonkers (Mors and Jonkers 2017a;Mors and Jonkers 2017b) who studied the effect of calcium lactate derivate as microencapsulated healing precursor during the last decade.…”

“…As a result, the maximum crack width that their system could heal after 100 days of incubation (i.e., 20°C, RH>95% and water submersion) was 650 µm. Pungrasmi et al 2019 investigated the effects of 2% w/w of capsules composed of sodium alginate and bacterial spores (Bacillus sphaericus LGMG 22257) added in Portland cement (CEM I) mortar. After 7 days of healing incubation (i.e., wet/dry cycles of water), their system demonstrated a SHC equal to 95% for cracks 200-300 µm wide, while their control plain mortar mixture had 73%.…”

Microencapsulation of tris(dimethylaminomethyl)phenol using polystyrene shell for self-healing materials

“…Inherent brittleness and faultiness of polymeric composites make them apt to form microcracks, propagating to failure 2 . Recently, smart materials [3][4][5] inspired from the biological systems were developed to repair inside damage whenever and wherever it occurs during the lifetime of polymeric composites, which would provide a method to significantly extend the service life and reliability of polymeric structural composites [6][7][8][9][10][11] . To realize this purpose, a series of strategies have been exploited such as embedded healing microcapsule and its curing agent 12,13 , embedded dual-microcapsule including healing agent and hardener [14][15][16] , embedded vascular network containing healing agent [17][18][19][20][21] , and so on [22][23][24] .…”