الفهرس 
CHAPTER (1) INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Reinforcement corrosion and the concrete strength reduction are critical problems that resulted from crack creation in concrete. Very expensive and hazardous technologies based on chemical materials have been provided for repairing the cracks. Recently, crack repair using bio-catalysis precipitating bacteria has been developed as a viable and ecofriendly alternative technique.
The main target of this study is to select and identify bacterial isolates with high urease activity to use in filling the cracks by the precipitation of CaCO3, and improve the characteristics of the concrete using two endospores forming and alkali-tolerant bacterial isolates that are designated as B1 and B2.
In our study, the isolates were identified using 16s rRNA gene sequencing with high similarities to Bacillus Wiedmannii (B1) and Bacillus Paramycoides (B2), and then submitted to GenBank NCBI database and had accession numbers (MZ434881 & MZ430955). Bacteria were incorporated both directly and by immobilization on two carriers such as light weight aggregate (LWA) and encapsulation for introduction into concrete mixture. The bacterial spores were added to the concrete mixture with a concentration 1.3 × 107 cells/cm3 by their immobilization on wood ash units.
The mixtures design and testing program was conducted in accordance with ECP and ASTM standards. Twenty-one mixtures containing different type, and carries of bacterial spores were designed. The compression and self-healing were carried out for hardened concretes at different curing times of 7, 14, and 28 days. 40x40x160 mm beam molds were used for mortar specimens, and 100 mm cubic, 100x100x500 mm beam, 100x200 mm cylinder, 1400x250x120 mm beam, and 150x300 mm cylinder molds were used for concrete specimens.
The all-fresh concrete mixtures were prepared to achieve standard workability (slump). The compression, flexural, indirect splitting tensile strength tests were carried out for hardened concretes at 28 days. Twelve beams were examined to evaluate the effect of the bacterial spores in concrete mixture on the shear and flexural strengths of reinforced concrete beams, and the crack healing efficiency.
Both bacterial species completely heal cracks in fully destructed concrete. The calcite filling of cracks and CaCO3 crystals that were screened using a scanning electron microscope may explain the crack healing and the enhancement in concrete strength. The results indicated an improvement in the compressive, indirect splitting tensile, shear, moment strength, and elastic modulus. Complete healing was observed in reinforcement concrete beams. In our study, it is the first time to discuss the effect of bacterial concrete on shear, and moment strength.