[01] Saad Issa Sarsam, Department of Civil Engineering, College of Engineering, University of Baghdad, Baghdad, Iraq. [02] Mohamed Fadhel Suliman, Department of Highways and Transportation, University of Al-Mustansiria, Baghdad, Iraq.

Bacterial concrete is considered as an innovative environmentally friendly method of construction. In this work, control and bacterial concrete specimens (cube, cylinder, and prism) have been prepared and cured in the laboratory for 28 days. A soil bacterium named Bacillus subtilis was cultured in the laboratory, the concentration of bacteria cells of B. subtilits in normal saline (NaCl, 9 g/l) suspension was 106 cell/ml. Such bacteria were added to the mixing water. Specimens have experienced the pulse velocity determination, then were divided into two sets. The first set was subjected to alter freezing-thawing cycles, while the second set was subjected to alter wetting-drying cycles. It was observed that the pulse velocity of bacterial concrete after 60 alter cycles of (freezing and thawing) is higher than that of control concrete (without bacteria) for cubes, cylinders and prisms by (18.4, 3.4 and 8.8)% respectively. While, the pulse velocity of bacterial concrete after 60 cycles of (wetting and drying) exhibit higher values than that of control concrete (without bacteria) for cube, cylinder and prism specimens by (17.4, 3.5 and 5.28)% respectively. Specimens were then assessed using the scanning electron microscope SEM. It was observed that the crack is filled by the CaCO₃ precipitation calcite crystals produced by Bacillus Subtilis. A layer of white precipitates all over the surface of the specimen with bacteria can be noticed indicating that the calcium carbonate crystals were very well developed near the surface of the crack.

Bacterial Concrete, Non-Destructive Test, Durability, Freezing, Thawing, Scanning Electron Microscope, Wetting

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