The doctor examines the affected parts of skin and asks about the symptoms. They may take a skin sample to rule out other similar skin conditions. That involves scraping off a small amount of skin and treating it with a chemical agent to identify fungal spores under a microscope. The results are often available the next day. In rare cases, a fungal culture will be grown in a laboratory in order to determine the exact strain of fungus. That takes around three weeks.
Moreover, a binary self-healing system containing CaO2 (a kind of ORC) and spore has been developed in our previous study [7]. ORC is selected and utilized to enhance the calcium precipitation deep inside the concrete crack where O2 is not available. In the presence of oxygen, spores are proved to germinate more effectively and maintain high metabolic activity, resulting in 3 times induced calcium precipitation more than that obtained without oxygen supply [7]. However, considering that the presence of ORC leads to alteration of environmental situations like dissolved oxygen (DO) and pH, different influential factors on the improvement of microbial calcium precipitation in the presence of ORC need to be further optimized, such as spore concentration, CaO2 dosage, carbon source and nitrogen source.
Spore 15 1 Patch With Crack
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.
Self-healing concrete is the ability of concrete to repair its small cracks autonomously and has recently become of interest in civil engineering. Several processes are proposed for the concept of self-healing concrete technologies, and are grouped as (1) natural, (2) chemical and (3) biological processes3. However, biological self-healing concrete is regarded as an environmentally friendly and economical technology, with the potential for diverse engineering applications, such as to remove heavy metals and radionuclides4, CO2 sequestration5, microbial enhanced oil recovery6 and restoration of construction materials, such as soil, limestone and concrete7,8,9.
The relevant bacterial spores and other required agents (nutrients and precipitation precursor) are added into the concrete during the mixing process. When cracking of the concrete occurs the embedded spores in the cracked zone would be activated by the moisture and O2 exposure, leading to their enhanced metabolism with the precipitation of CaCO3 to heal the cracks13. However, direct incorporation of bacteria into the concrete, dramatically reduces the microbial metabolic activity14, and so microencapsulation is essential to enhance the bacterial viability in the extreme conditions for a longer period of time. In this approach, the bacterial spore is encapsulated in a protective carrier, like a polymer or microcapsule15 that can resist the high pH and humidity limitations of concrete, including the mechanical forces during the concrete preparation processes16. On the other hand, they should easily break open when cracks appear so as to release the spores to germinate and subsequently precipitate CaCO3 to heal the cracks17.
In practice, microencapsulation technologies have mostly been applied for medical treatment, pharmacy applications, food industry and agricultural fertilizer. However, this technology can likely be used for the MICP of bacterial spores in concrete to ensure their viability and metabolic activity during long term usage in concrete. Previous studies have only focused on the crack healing efficiency, while the viability of the bacteria remains unknown. The objective of this study was to determine a suitable microencapsulation technique to preserve the bacterial spores of Bacillus sphaericus LMG 22257 incorporated in self-healing concrete. The experimental work consisted of comparing the performance of three techniques to encapsulate the bacterial spores (extrusion, spray drying and freeze drying) in terms of the spore survival rate and encapsulation yield (EY). The viability of the bacteria after the mortar preparation process was evaluated by their urease activity. The results of this study indicate the most appropriate microencapsulation technique for self-healing concrete.
To ensure that most of cells become spores after the heat-shock step and spore germination process, microscopic examination and endospore gram staining were evaluated. The number of spores were compared before and after these inducing steps. Malachite green staining, a specific stain of endospores, clearly confirmed that sporulation occurred. The proportion of red rod-shaped bacterial cells that contained a green space (spore) within the terminal region of the cell indicated that an average of 90% of the cells were present as spores.
To investigate the viability of microencapsulated bacterial spores after mixing with mortar, the level of urea hydrolysis (urease activity) was measured. This indirect spectrophotometric measurement at A422 was used to reveal the number of viable (germinated) spores based upon the direct release of urease by viable bacteria that then catalyzes the hydrolysis of urea. Thus, the hydrolyzed urea refers to the bacterial spore ureolytic activity. If the amount of hydrolyzed urea is high, it indicated more metabolically viable cells and hence that the microencapsulated bacterial spores can survive and remain viable after being mixed in the mortar specimens. The hydrolyzed urea increases depending on time. During the first phase (lag phase), the bacterial spores adjust to the environment, undergoing metabolic changes and storing nutrients prior to subsequently germinating as a vegetative cell or cell active form. The ureolytic activity during this initial phase is quite low. When the bacterial cells enter the exponential or log phase, when the cells were dividing, the cells are metabolically active and synthesize and secrete urease, thereby the ureolytic activity was high then the hydrolyzed urea increased.
The biological self-healing process of concrete is mainly mediated by the microbial precipitation of CaCO3, and so measurement of the repaired part of the crack can indicate the self-healing efficiency. The main purpose of this work is to evaluate the performance of microencapsulated bacterial spores on the self-healing of concrete by crack filling, which was assessed by the visualization of the crack area before and after healing. The 50-mm3 mortar samples were prepared as in the viability test. The samples were prepared with the addition of 2% (w/w of the cement weight) of freeze dried capsules, nutrient and calcium ion source. After 28 d curing, cracks were induced in the mortar samples by subjecting them to a monotonic compression test. All mortar samples were incubated in a wet-dry cycle in water for 7 d. In this research, a wet-dry cycle incubation was used to simulate the moisture changes in concrete structure due to rain or water. During the wet period, the specimens could absorb enough water, which can remain some moisture in the intercellular matrix during the dry period. When the specimens were exposed in the air, more oxygen becomes available for the bacteria. A wet-dry cycle can accelerate the diffusion of the nutrients from the intercellular matrix to the surficial crack zone without excessive leaking to the bulk solution. This process can also keep the specimens with enough water for bacterial activities during the dry period.
The progress of the crack healing process was followed by the images of the crack area taken at each indicated time interval. The healing ratio of the initial and final crack area in the images were determined by the image processing. Examples of crack areas are shown in Fig. 5, where it was obviously indicated that the crack can be gradually healed with the increase of time. The crack width measurement are also summarised in Table 2. The crack area of the mortar specimen without microencapsulated bacterial spores gave a healing ratio of 72.7%, which was less than that with the encapsulated bacterial spores (95.4%). Thus, bacterial spores encapsulated by sodium alginate via freeze drying can enhance the crack healing efficiency by their biochemical activity and so can possibly be used as a microencapsulation technique for MICP spores for application in concrete technology.
The viability of bacteria is the most crucial issue in applying MICP for self-healing concrete technology. Microencapsulation of bacterial spores with a protective carrier offers a solution to the problem of an otherwise low cell viability in a concrete environment. In this study, the potential microencapsulation techniques were comparatively studied. The three techniques to prepare sodium alginate encapsulated bacterial spores (extrusion, spray drying and freeze drying) had the potential to protect and preserve bacteria in the concrete mixing and hardening environments. Freeze drying provided the highest spore survival rate and viability, which is because the freeze-dried capsules were less influenced by the encapsulation process and had a low rupture rate during the concrete mixing and hardening stage. In addition, freeze-dried capsules still performed their biological activity to induce CaCO3 precipitation for the self-healing of concrete. Therefore, freeze drying can possibly be used as a microencapsulation process for MICP spore applications in concrete technology. The key discussions from the study can be pointed out as follows. 2ff7e9595c
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