Digital Image Processing for Precise Evaluation of Crack Repair in Concrete using Bio-Inspired Strategies

Abstract

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 for concrete repairs. This study investigated the adequacy of Microbially induced calcite precipitate for mortar crack repair by using a non-ureolytic (avoid production of ammonia) alkaliphilic bacterial strain (high pH of cementitious matrix) with calcium source. Biological metabolic activity of Bacillus pumilus with Calcium lactate were used for crack repair. As Bacillus pumilus was first time reported for concrete repair, so germination and growth characteristics were evaluated in control microbiology laboratory before application. The healing potency by bacterially mediated calcium carbonate was precisely investigated by Digital image processing using 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 was evaluated through water permeability, water tightness, ultra-sonic measurement and compressive strength recovery of. Sample treated with bacterial treatments exhibited enhance permeability and water tightness comparable to any other conventional treatments. The bacterial repaired mortar samples shown enhanced values of ultra-sonic measurement and recovered compressive strength equivalent to conventional repair. The enhanced durability of bacterially repaired mortar sample is due to presence of dense precipitated of CaCO3 by metabolic activity of bacteria. Micro-structural evaluation was done for CaCO3 confirmation from collected precipitate inside healed crack by biological repair. Raman spectroscopy of precipitates revealed presence of CaCO3 single peak corresponding to the Ag internal mode at 1085 cm-1 from v1 symmetric stretching of carbonate ion. X-Ray diffraction analysis of precipitate exhibit intense peaks of CaCO3 at 2-theta (2θ) orientation of 29.45 ͦ . Micrographs obtained from Scanning electron Microscopy (SEM) shown dense CaCO3 crystal where composition of crystals was confirmed by Spot Energy dispersive X-ray (Spot-EDX). Thermogravimetric analysis results of bacterial healing precipitate shown significant weight loss between 600°C and 750°C, confirming presence of CaCO3. All these Micro-structural, chemical and physical analysis confirmed enhanced durability of bacterially treated mortar specimen is due to CaCO3 deposition inside crack.