<p>In order to find suitable bacteria as concrete healing agents, we
examined a total of 50 bacterial isolates from an alkaline soil sample. These
isolates were subsequently tested for sporulation rates, ability to induce
calcium carbonate precipitation, tolerance to alkaline conditions, as well as
their capacity to heal cracks in mortar samples. Of the 50, two bacterial isolates showed promising results across all these test
categories. These isolates were identified as <i>Bacillus horneckiae</i> and <i>B.
kochii</i>. Both were able to grow on LB agar at a pH of 10, within 5 days had
sporulation rates over 90% on the AR2A agar plates, and precipitated calcium
carbonate on B4 agar plates. </p>
<p>Both <i>B. horneckiae </i>and<i> B. kochii</i> had
preferences for high alkaline environments. The OD 540nm readings of these two
bacteria in pH 9 and 10 LB broths were significantly higher than the readings
of their counterparts in pH 8 LB broth after 48 h of incubation. The growth of <i>B.
horneckiae </i>and<i> B. kochii</i> in different concentrations of YE broths
were tested. These two bacteria both had worse growth in 0.5 and 1% YE broths
than in 2% YE broth. The spores of <i>B. horneckiae </i>and<i> B. kochii</i>
were also tested for germinations in the same test environments. Results showed
that either high pH or low nutrient levels did not have many impacts on spore
germinations of these two bacteria. </p>
<p>Calcium carbonate precipitation from these two bacteria were quantified. <i>Bacillus
horneckiae </i>and<i> B. kochii </i>reduced approximately 980 and 650 ppm of
free<i> </i>Ca<sup>2+</sup> ion respectively from a 1/10 LB broth containing
2500ppm of Ca<sup>2+</sup> within 7 d and precipitated CaCO<sub>3</sub>.</p>
<p>The mean viable counts of <i>B. horneckiae </i>and<i> B. kochii</i>
decreased 1.2 and 1.5 orders of magnitude respectively in the first 24 h, dropped additional 0.6 and 0.4 orders of
magnitude between day 1 and 14, and then, remained
constant between day 14 and 28 after being mixed in mortar samples. Healing
abilities were tested by incorporating bacterial spores in mortar samples.
Cracks up to 0.25 mm were healed in mortar samples containing <i>B. horneckiae </i>or
<i>B. kochii </i>spores<i>.</i> All the results suggested that both the
bacterial isolates, <i>B</i>.<i> horneckiae </i>and<i> B. kochii</i>, may be
used as bacterial healing agents in self-healing concretes.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/13380062 |
| Date | 16 December 2020 |
| Creators | Yen Hao Chiao (8306043) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/SCREENING_FOR_ALKALINE_RESISTANT_SPORE_FORMING_BACTERIA_AS_CONCRETE_HEALING_AGENTS/13380062 |
Page generated in 0.0015 seconds