Bio-Inspired Self-Healing Cementitious Mortar Using Bacillus Subtilis Immobilized On Nano/Micro Additives

Abstract

High strength, durability and low cost make concrete one of the most used construction material in the world. In the service life span of cementitious composites, the generation of cracks is inevitable. These micro level cracks hamper the durability while their transformation into macro level causes problems of structural integrity and capacity reduction. For maintaining serviceability of the structures repair/maintenance has to be undertaken which is usually costly, difficult and environmentally unfriendly. Therefore, the inclusion of nano/micro sized self-healing materials may be beneficial not only in terms of automatic cracks healing but improved durability, cost effectiveness and eco-friendly. Self-healing concrete repairs/mends the crack by utilizing compounds, resins and microorganisms added to concrete in the mixing stage. Bio-inspired self-healing cementitious composites has the capability of repairing cracks by producing chemical products from the microorganisms and precursor compound incorporated during mixing phase. The incorporated bacteria remain dormant in the matrix until cracking occurs and water seeps in the cracks. The ingress water activates the bacteria, which utilize the precursor compound to fill cracks hence inhibiting strength loss and increasing durability of concrete structures. In the present research, Bacillus subtilis bacteria were grown and incorporated in mortar specimens using various nano and micro sized carrier particles of iron oxide, limestone and siliceous sand. The resulting cement composites were analyzed for their crack healing capabilities and also for mechanical characteristics, microstructure and phase configuration. The results indicated that the iron oxide particles as carrier material are more efficient in crack healing throughout the life span of cement mortar composites whereas limestone and siliceous sand particles produced promising results at initial age (3 and 7 days) and later age (28 days), VI respectively. All the incorporation techniques exhibited an enhanced compressive strength as compared to control.