Repair of mortar cracks using Bacillus pumilus based bio-suspension assessed by machine learning algorithm for image processing

Abstract

Shortcomings and contagious effect to the environment by existing concrete repairs have drawn interest to alternative solutions for concrete repair. In this study, Bio-suspension was prepared to repair pre-existing cracks on the mortar surface. Bio-suspension of a rarely explored alkaliphilic, spore-forming bacterial strain Bacillus pumilus is reported for the first time for repair. The biological metabolic activity of Bacillus pumilus is capable of calcite precipitation in a high alkaline environment of cementitious matrix. Samples repaired by both bio-suspension and conventional treatments were investigated against water permeability, ultra-sonic pulse velocity, crack sealing, and compressive strength. The machine-learning algorithm of image processing was used for acquiring crack features of pre-existing mortar surface cracks and the healing potency. OTSU method of thresholding was used in image processing. The results indicated that precipitated calcite by prepared bio-suspension successfully healed crack up to 1.55 mm. Alongside crack sealing, formulated bio-suspension showed 3 order lower value of water permeability in comparison to untreated cracked samples. Further, a significant increase in the value of ultra-sonic transmission and improved compressive strength of repaired samples is attained. The results obtained with bio-suspension were equivalent to conventional epoxy-based repair. Further, microstructural analysis of precipitates of bio-repair by SEM-EDX, XRD, RAMAN, and TGA confirmed the adequate presence of calcite crystal due to metabolic activity of introduced Bacillus pumilus inside the cracks.