A Novel Microbially Induced Self-Healing Cement/Concrete for Underwater Concrete Offshore Structures

Abstract

Techniques for offshore structure concrete remediation have received minimal consideration in the oil and gas industry in spite of its potential. Emerging "bio-concrete" to plug micro-cracks have shown concrete results in various lab experimentations. Recently, MICP technology has garnered world-wide attention and popularity for various multi-disciplinary applications where smart synthesis of calcium carbonate minerals generate at ambient conditions contributing to bio-cemented self-healing agents by mixing bacteria into the cement slurry. Concrete fails to self-heal and repair cracks greater than 0.2 micron. The technique comprises of mixing the preparatory material with operative quantities of urease producing spores and a calcium ions under standard conditions of hydrolyzed urea. Scientists found that microbes extensively multiply when nutrients comprising of cheap carbon sources like molasses/glycerol is added to the mixture. Live microbes propagate via cracks channels and micro-voids and smartly cement the cracks by calcifying the matrix structure. Bacteria can then act as a autogenous self- healing agent. The precipitating bacterial strains generate urease enzyme which metabolically precipitate calcium minerals in the neighboring environment as calcium carbonate. The degradation of urea via bacterial metabolism locally rises the surrounding pH allowing the carbonate microbial calcification. These precipitates can autogenously plug the cracks and improve concrete robustness. The calcifying bacteria can be secluded from cement matrix or various natural sources. The purified spores can cultivate for limited time periods and then supplemented to the concrete matrix for application. The spores remained viable after prolonged periods. After short curing times, the healing capability of micro-cracks, durability, and tensile strength showed significant improvement. This novel approach of crack plugging is highlighted to save substantial costs associated with crack restoration and repair of underwater concrete offshore structures and platforms.