Digital image processing for precise evaluation of concrete crack repair using bio-inspired strategies

Abstract

• Bacillus pumilus was analyzed in retrofitting of mortar for the very first time. • Digital image processing is employed in monitoring crack healing. • Bio-Consortia significantly reduced the permeability of repaired mortar specimens. • Microbial repair is the potential and sustainable alternative to conventional repairs. Inadequacy of surface coatings and deleterious action to the environment by epoxy-based solution for surface treatment have received the attention for more sustainable techniques of concrete repair. This paper investigated the adequacy of Microbially induced calcite precipitate for mortar crack repair by using a non-ureolytic (avoid the production of ammonia), alkaliphilic bacterial strain with calcium source. The biological metabolic activity of Bacillus pumilus with Calcium lactate was used for crack repair. As Bacillus pumilus was first time reported for concrete repair, germination and growth characteristics were evaluated in the control microbiology laboratory before application to repair. The healing potency by bacterially mediated calcium carbonate was precisely investigated by Digital image processing using the OTSU method of thresholding. Crack healing of 99 – 100 % was achieved by biological repair for mortar samples having average crack width varying from 0.29 to 1.55 mm. The efficacy of crack repair by both bacterial repair and conventional treatments were evaluated through water permeability, water tightness, ultra-sonic measurement, and compressive strength recovery. The samples treated with bacterial treatments exhibited enhanced permeability and water tightness comparable to any other conventional treatments. The bacterial repaired mortar samples showed enhanced values of ultra-sonic measurement and recovered compressive strength equivalent to conventional repair. The enhanced durability of bacterially repaired mortar samples is due to the presence of dense precipitated CaCO 3 by the metabolic activity of bacteria. Further, forensic evaluation confirmed the formation of CaCO 3 in bio-precipitate as a result of metabolic activity triggered by inoculated bacterial consortia.