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IJSTR >> Volume 9 - Issue 2, February 2020 Edition



International Journal of Scientific & Technology Research  
International Journal of Scientific & Technology Research

Website: http://www.ijstr.org

ISSN 2277-8616



Self-Healing Development AND Performance Assessment OF Bio Cementitious Concrete

[Full Text]

 

AUTHOR(S)

Joe-Sam Nkuah, Manish Kaushal and Sandeep Singla.

 

KEYWORDS

Bacillus subtilis, Bio mineralization, Calcium carbonate precipitate, Healing agents, Self-healing, Strength regain, and Precursor compound.

 

ABSTRACT

A bio cementitious concrete is basically a construction material (concrete) which has been incorporated with bacteria and precursor compound as healing agent that awaken and seal cracks when they emerge. The bacteria act as a catalyst, and transform the precursor compound to limestone and this technique is based on bio mineralization of bacteria. In this research, an extensive work was undertaken to investigate self-healing development and performance assessment of bio cementitious concrete, and this was carried off by integrating Bacillus Subtilis into engineered cementitious composites (ECC), normal mortar, and concrete alongside with calcium lactate, urea and yeast extract as nutrient source for the bacteria. After carrying out all the tests of culturing, growing and checking pH and temperature resistivity of the bacteria. The bacterial cell solution was integrated into the concrete matrix by adopting, immobilization of bacterial cell in pumice solution, encapsulation of stiffen bacteria sand and immobilization of bacterial cell into porous expansive clay particles as techniques for adding and protecting the bacterial cell inside the concrete. During the mixing and specimen preparation stage, three bacterial cell solutions of concentrations (104,106,108)cells/ml were prepared and mixed with M25 mortar and normal concrete by using mix ratios 1:1:2 , 1:1.32:2.5 with water/cement ratio of 0.5. Again the bacterial cell solution was mixed with M40 ECC of water/binder ratio of 0.33 and sand/ binder ratio of 1: 0.84.The bacteria reacted with the concrete elements to form calcium carbonate precipitate (CaCO3) or limestone which successfully sealed the created cracks. Performance assessment was done on the specimens and the following results were obtained; at a concentration of 104cell/ml of bacterial cells, the compressive strength of concrete begins to increase to an optimum value at 106cell/ml and declines at 108cell/ml. The specimens of stiffen sand capsules, pumice immobilized bacterial cell and loaded clay particle at 2% replacement by coarse aggregates weight increased the compressive strength of concrete by 35.20%, 31.59% and 0.20% respectively at the end of 28 curing days. Cracked Stiffen sand capsules and pumice immobilized bacterial cell ECC specimen regained flexural strength of 23.6% and 32.22% at the end of 56 self-healing days. Sorptivity at end of 56 days for self-healed stiffen sand capsules, pumice immobilized bacterial cell and loaded clay particle concrete specimens were reduced by 70.1%, 70% and 81.9% respectively. The bacterial incorporated concrete specimens with crack width of 0.015 mm, 0.018 mm and 0.02 mm respectively were completely sealed by CaCO3 precipitate at the end of 56 self-healing days. The new material formed at crack areas was CaCO3 according to the X-Ray Diffraction spectra obtained. Based on these factors, it is concluded that the bio cementitious concrete showed excellent performance assessments in terms of compressive strength, sorptivity reduction, flexural strength, crack repair and crack recovery strength at the end of 56 self-healing day.

 

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