Factors affecting crack repairing capacity of bacteria-based self-healing concrete

• Bacteria-based self-healing concrete was developed.
• Bacteria induced precipitations at cracks were analyzed by SEM and XRD.
• The crack self-healing effect under different conditions were studied.
• The image characterization method was used for crack-healing quantification.

Bacteria-based self-healing concrete is a relatively new technique, therefore it is important to gather more results in simulate real conditions before applied on a bigger scale. In the present study, bacteria-based self-healing concrete was developed by adding the microbial self-healing agent which has the potential to improve self-healing capacity mainly by bacteria induced mineral precipitations. The precipitations formed at the cracks surface of the cement paste specimens were analyzed with Scanning Electron Microscope (SEM) equipped with an Energy Dispersive X-ray Spectrometer (EDS), and then examined by X-ray Diffraction (XRD). Moreover, the influence of crack width, curing ways and cracking age on the crack self-healing of cement paste with microbial self-healing agent was researched by the characterization methods of area repair rate and anti-seepage repair rate. The results showed that the microbial self-healing agent could be used to achieve the goal of concrete crack self-healing. The precipitations formed at the cracks surface were calcite, which appeared lamellar close packing morphology. However, the capacity of concrete crack self-healing depended on many factors. The crack was more and more difficult to be repaired with the increase of average crack width and the repair ability of microbial repair agent was limited for specimens with crack width up to 0.8 mm. Water curing was shown to be the best way for bacteria-based self-healing concrete. In addition, the crack healing ratio of specimens dropped significantly along with the extension of cracking age. When the cracking age was more than 60 days, the crack healing ratio was very small. The results above suggested that the optimal conditions were needed for the practical application of microbial self-healing agent.