Self-Healing Concrete by Biological Substrate

Abstract

At present, the commonly used repair materials for concrete cracks mainly include epoxy systems and acrylic resins, which are all environmentally unfriendly materials, and the difference in drying shrinkage and thermal expansion often causes delamination or cracking between the original concrete matrix and the repair material. This study aimed to explore the feasibility of using microbial techniques to repair concrete cracks. The bacteria used were environmentally friendly Bacillus pasteurii. In particular, the use of lightweight aggregates as bacterial carriers in concrete can increase the chance of bacterial survival. Once the external environment meets the growth conditions of the bacteria, the vitality of the strain can be restored. Such a system can greatly improve the feasibility and success rate of bacterial mineralization in concrete. The test project included the microscopic testing of concrete crack repair, mainly to understand the crack repair effect of lightweight aggregate concrete with implanted bacterial strains, and an XRD test to confirm that the repair material was produced by the bacteria. The results show that the implanted bacterial strains can undergo Microbiologically Induced Calcium Carbonate Precipitation (MICP) and can effectively fill the cracks caused by external concrete forces by calcium carbonate deposition. According to the results on the crack profile and crack thickness, the calcium carbonate precipitate produced by the action of Bacillus pasteurii is formed by the interface between the aggregate and the cement paste, and it spreads over the entire fracture surface and then accumulates to a certain thickness to form a crack repairing effect. The analysis results of the XRD test also clearly confirm that the white crystal formed in the concrete crack is calcium carbonate. From the above test results, it is indeed feasible to use Bacillus pasteurii in the self-healing of concrete cracks.

Keywords: Bacillus pasteurii bacteria; crack repair; self-healing concrete.

Figure 1

Appearance of lightweight expanded shale aggregates.

Figure 2

Lightweight aggregate containing biological species: (a) soaked once; (b) soaked twice.

Figure 3

Curing situation of specimens: (a) control group and experimental group I; (b) experimental group II.

Figure 4

Unheated Bacillus pasteurii images: (a) SEI (upper detector image, 20,000 times magnification); (b) SEI (3000 times magnification); (c) LEI (lower detector image, 20,000 times magnification); (d) LEI (3000 times magnification).

Figure 5

Heated Bacillus pasteurii images: (a) SEI (20,000 times magnification); (b) SEI (3000 times magnification); (c) LEI (20,000 times magnification); (d) LEI (3000 times magnification).

Figure 6

Unheated Bacillus pasteurii image (stained).

Figure 7

Heated Bacillus pasteurii image (stained).

Figure 8

Confirmation of activity after sporulation of the strain (replanting of bacterial solution).

Figure 9

Confirmation of activity after sporulation of the strain (replanting of aggregate containing biological species).

Figure 10

Confirmation of activity after sporulation of the strain (urease reaction).

Figure 11

Mold of the beam specimen.

Figure 12

Pre-cracking of the concrete cylindrical specimen by the splitting method.

Figure 13

Images of the pre-cracked concrete cylindrical specimen (Control group): (a) Day 1; (b) Day 28; (c) Day 56; (d) Day 91.

Figure 14

Images of the pre-cracked concrete cylindrical specimen (Experimental group I): (a) Day 1; (b) Day 28; (c) Day 56; (d) Day 91.

Figure 15

Images of the pre-cracked concrete cylindrical specimen (Experimental group II): (a) Day 1; (b) Day 28; (c) Day 56; (d) Day 91.

Figure 16

Pre-cracking of the beam specimen by the bending method.

Figure 17

Images of the pre-cracked concrete beam specimen with small cracks (Experimental group II): (a) Day 1; (b) Day 3; (c) Day 7; (d) Day 14; (e) Day 21; (f) Day 28; (g) Day 56; (h) Day 91.

Figure 18

Images of the pre-cracked concrete beam specimen with large cracks (Experimental group II): (a) Day 1; (b) Day 3; (c) Day 7; (d) Day 14; (e) Day 21; (f) Day 28; (g) Day 56; (h) Day 91.

Figure 19

Comparison of cross-section observations between the control group and experimental group II: (a) control group; (b) experimental group II.

Figure 20

Sectional observation of experimental group II under a portable microscope: (a) 100 times magnification; (b) 200 times magnification.

Figure 21

Surface crack of the concrete specimen.

Figure 22

Crack repair of the concrete specimen.

Figure 23

Thickness observation of the vertical section crack repair under a portable microscope (100 times magnification).

Figure 24

XRD test results of crack repair powder (experimental group I): (a) result at the sample center; (b) result at the sample surface.

Figure 25

XRD test results of the crack repair powder (experimental group II): (a) result at the sample center; (b) result at the sample surface.