A sustainable solution for crack maintenance in geopolymers is necessary if they are to be the future of modern green construction. This study aims to develop self-healing biogeopolymers that could potentially rival bioconcrete. First, a suitable healing agent was selected from Bacillus subtilis, Bacillus sphaericus, and Bacillus megaterium by directly adding their spores in the geopolymers and subsequently exposing them to a precipitation medium for 14 days. Scanning electron microscope with energy-dispersive X-ray (SEM-EDX) analysis revealed the formation of mineral phases for B. subtilis and B. sphaericus. Next, the effect of biochar-immobilization and co-culturing (B. sphaericus and B. thuringiensis) on the healing efficiencies of the geopolymers were tested and optimized by measuring their ultrasonic pulse velocities weekly over a 28-day healing period. The results show that using co-cultured bacteria significantly improved the observed efficiencies, while biochar-immobilization had a weak effect, but yielded an optimum response between 0.3–0.4 g/mL. The maximum crack width sealed was 0.65 mm. Through SEM-EDX and FTIR analyses, the precipitates in the cracks were identified to be mainly CaCO3. With that, there is potential in developing self-healing biogeopolymers using biochar-immobilized spores of bacterial cultures.
The study investigated the effect of storage conditions on the stability of electrolyzed seawater (ESW)’s physicochemical properties (pH, oxidation-reduction potential (ORP), and free chlorine (FC) concentration), and bactericidal efficiency on the fecal coliform Escherichia coli for 30 days. Preliminary experiments were conducted to determine the optimal current and electrolysis time. Two batches of 2750 mL filtered seawater were electrolyzed using 50 mm × 192 mm platinum–titanium mesh electrodes at a current of 1.5 A for 20 min. One hundred milliliters of electrolyzed solution was transferred into each amber glass and high-density polyethylene (HDPE) bottles. The bottles were stored in a dark area at ambient temperature. The results showed an increase in pH and a decrease in ORP and FC concentration through time. Hypochlorous acid remained as the dominant component since the pH levels of the solutions remained below 7.5. FC decay was investigated using Chick’s Law. It was determined that the decay in HDPE bottles (k = −0.066 day−1) was faster compared to amber glass bottles (k = −0.046 day−1). Nonetheless, HDPE bottles could still be used as an alternative container for 30 days only due to observed instability beyond 30 days. ESW remained effective since no surviving population of E. coli was observed throughout the experimentation.
Electrolysis of seawater has the ability to produce free chlorine (FC), sodium hypochlorite (NaClO), hypochlorous acid (HOCl) and other oxidants which enable it to kill pathogens making it a viable disinfectant. However, the stability of this disinfectant is somewhat unpredictable during storage. This study determined the effects of storage time on the stability of electrolyzed seawater (ESW) in terms of its physicochemical properties, specifically pH, oxidation-reduction potential (ORP), and free chlorine concentration (FCC) for 83 days and evaluated its disinfection performance on Pseudomonas aeruginosa. The effect of dilution in the disinfection was also investigated at ESW to water ratio of 1:0, 1:1, and 3:6. Pre-filtered seawater was electrolyzed at 1.5 A for 20 minutes using platinum-coated titanium mesh electrodes. The ESW was transferred to opaque high-density polyethylene (HDPE) bottles stored at ambient temperature without direct exposure to sunlight. The physicochemical properties of ESW at different storage times were determined, and its disinfection capability against P. aeruginosa was evaluated. This study has made use of two trials for the physicochemical test due to two different batches of seawater were taken. pH was found to increase over time, having a range of 6.32 to 7.705. The ORP and FCC, on the other hand, decreased over time. In accordance with the literature found, the pH ranges show that hypochlorous acid is the main driver of disinfection. Complete disinfection of ESW at 3:6 dilution was observed until 48 days of storage, while the 1:0 dilution was until 83 days and 1:1 dilution was until 51 days. FC decay (k=-0.1449 day−1 and k=-0.0544 day−1) was determined using Chick’s Law. Even at different dilution levels, ESW still proved its bactericidal efficacy in this research.
A sustainable solution for crack maintenance in geopolymers is necessary if they are to be the future of modern green construction. This study thus aimed to develop self-healing biogeopolymers that could potentially rival bioconcrete. First, a suitable healing agent was selected from Bacillus subtilis, B. sphaericus, and B. megaterium by directly adding their spores in the geopolymers and subsequently exposing them to a large amount of nutrients for 14 days. SEM-EDX analysis revealed the formation of biominerals for B. subtilis and B. sphaericus. Next, the effect of biochar-immobilization and co-culturing (B. sphaericus and B. thuringiensis) on the healing efficiencies of the geopolymers were tested and optimized by measuring their ultrasonic pulse velocities weekly over a 28-day healing period. The results show that using co-cultured bacteria significantly improved the observed efficiencies, while biochar-immobilization had a weak effect but yielded an optimum response between 0.3-0.4 g/mL. The maximum crack width sealed was 0.65 mm. Through SEM-EDX and FTIR analyses, the biominerals precipitated in the cracks were identified to be mainly CaCO3. Furthermore, image analysis of the XCT scans of some of the healed geopolymers confirmed that their pulse velocities were indeed improving due to the filling of their internal spaces with biominerals. With that, there is potential in developing self-healing biogeopolymers using biochar-immobilized spores of bacterial cultures.
A sustainable solution for crack maintenance in geopolymers is necessary if they are to be the future of modern green construction. This study thus aimed to develop self-healing biogeopolymers that could potentially rival bioconcrete. First, a suitable healing agent was selected from Bacillus subtilis, B. sphaericus, and B. megaterium by directly adding their spores in the geopolymers and subsequently exposing them to a large amount of nutrients for 14 days. SEM-EDX analysis revealed the formation of biominerals for B. subtilis and B. sphaericus. Next, the effect of biochar-immobilization and co-culturing (B. sphaericus and B. thuringiensis) on the healing efficiencies of the geopolymers were tested and optimized by measuring their ultrasonic pulse velocities weekly over a 28-day healing period. The results show that using co-cultured bacteria significantly improved the observed efficiencies, while biochar-immobilization had a weak effect but yielded an optimum response between 0.3-0.4 g/mL. The maximum crack width sealed was 0.65 mm. Through SEM-EDX and FTIR analyses, the biominerals precipitated in the cracks were identified to be mainly CaCO3. Furthermore, image analysis of the XCT scans of some of the healed geopolymers confirmed that their pulse velocities were indeed improving due to the filling of their internal spaces with biominerals. With that, there is potential in developing self-healing biogeopolymers using biochar-immobilized spores of bacterial cultures.
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