A binary concrete crack self-healing system containing oxygen-releasing tablet and bacteria and its Ca2+-precipitation performance

Abstract

A strategy to supply molecular oxygen for microbial calcium precipitation was developed for the first time. Firstly, a controlled oxygen-releasing tablet (ORT) containing CaO and lactic acid with a suitable ratio of 9:1 was developed. It can provide a stable oxygen supply and maintain pH in the range of 9.5-11.0 for 45 days while contacting with water. In the presence of oxygen, a self-healing bacterium H4 spores germinated more effectively and maintained high metabolic activity. Furthermore, H4 vegetative cells induced 50 % more calcium precipitation than that obtained without oxygen supply. Finally, a binary self-healing system containing bacterial spores and ORT was established. The calcium precipitation experiments showed that H4 in the binary self-healing system precipitated 27.5 mM calcium with oxygen supply after 32 days and dissolved oxygen (DO) concentration of the solution decreased from 15 to 4 mg l, while only 6.9 mM calcium precipitation was obtained without oxygen supply. This work can disclose the effect of oxygen on microbial calcium precipitation and further lay a foundation for the establishment of ternary self-healing system containing bacteria, ORT, and nutrients, which will be promising for the self-healing of cracks deep inside the concrete structure.

A Comprehensive Review of the Study and Development of Microcapsule Based Self-Resilience Systems for Concrete Structures at Shenzhen University

“…To deal with the problem mentioned above, a pioneer attempt at Shenzhen University has been made to develop a strategy to supply oxygen for the microbial calcium precipitation performance [39]. Firstly, a suitable peroxide was screened to develop an oxygen-releasing tablet (ORT) that can provide a stable oxygen supply.…”

“…Furthermore, a binary self-healing system which contains bacteria and ORT was established and the overall calcium-precipitating activity of the system was investigated. Details can be found in the reference [39]. …”

“…The calcium precipitation of the binary self-healing system was evaluated in bacteria medium solution, and the result was shown in Figure 17 [39]. …”

“…Furthermore, it can be noticed that the DO of the control (MCC/H4) was very low, which might account for the lower calcium precipitation by the bacteria in the absence of oxygen supply (Figure 17c). From Figure 17b, it can be found that involvement of the bacteria alleviated the fluctuation of pH during calcium precipitation [39]. …”

“…MCC and CPL1 represent the microcrystalline cellulose and oxygen release compound with the ratio of CaO 2 and lactic acid being 9:1, respectively: ( a ) DO and ( b ) pH; Calcium precipitation performance of binary microbial self-healing system. MCC and CPL1 represent the microcrystalline cellulose and oxygen release compound with the ratio of CaO 2 and lactic acid being 9:1, respectively: ( c ) Insoluble Ca 2+ and ( d ) soluble Ca 2+ [39]. …”