Crack healing in cementitious mortars using enzyme-induced carbonate precipitation: Quantification based on fracture response

This paper evaluates a nonmicrobial means of carbonate precipitation to heal cracks in concrete. Enzyme-induced carbonate precipitation (EICP) that relies on plant-derived urease enzyme is used to catalyze the reaction between calcium chloride and urea to precipitate calcium carbonate. The faster rate of carbonate precipitation and the absence of microbes makes this method attractive for surface applications for crack healing of concrete. Notched mortar beams in which precracking is induced are subjected to EICP solutions with different CaCl₂ concentrations and a fixed molar ratio of urea:CaCl₂ of 1.2. X-ray diffraction and thermal analysis of samples collected from the vicinity of the notch clearly demonstrate the presence of calcium carbonate in the cracks. A flexural strength enhancement of approximately 33% is observed for mortars treated with an EICP solution made using 0.5 M CaCl₂ compared with the mortars that are just moist cured, and the fracture toughness doubled. The strength and fracture parameters (fracture toughness and critical crack tip opening displacement) scale well with the carbonate content. Digital image correlation (DIC) is used to quantify the reduction in crack extension after the beams are treated with the EICP solution.