Behavior of Bacterial Concrete under Freezing and Thawing Cycles
Mohamed Fadhel Suliman1, Saad Issa Sarsam2*
1MSc. Student, Department of Highways and Transportation, University of Al-Mustansiria Baghdad, Iraq.
2Professor, Department of Civil Engineering, College of Engineering, University of Baghdad, Iraq.
Cracking exhibit a durability problem since the ingress of moisture and harmful chemicals such as sulphates and chlorides into the concrete through the cracks can cause premature matrix degradation and corrosion of embedded steel reinforcement, which may result in the decrement of strength and life. In this work, assessment of the durability of control and bacterial concrete was adopted by subjected the casted cubes, prisms and cylinder specimens to cycles of freezing and thawing. Concrete specimens of various type (cube of 100x100x100 mm, cylinder of 100 mm diameter and 200 mm height, and prism of 100x100x500 mm) sizes have been prepared in the laboratory, then separated to two sets (with and without bacteria). A soil bacterium named Bacillus subtilis was cultured in the laboratory, the concentration of bacteria cell of B. subtilits in normal saline (NaCl, 9 g/l) suspension was 106 cell/ml. Data was analyzed to assess its impact on the strength properties (compression, tensile and flexural strength). It was noticed that the precipitation of calcite by continuous hydration of cement helps in production of calcium carbonate precipitation with the help of bacteria. It was observed that the bacterial concrete at end of cycles of freezing and thawing (60 cycles) exhibits higher compressive, splitting tensile and flexural strength of 25.8%, 22.7% and 22% respectively than that of control concrete. It was concluded that implementation of the bacteria in the concrete mixture is beneficial to overcome the impact of freezing-thawing cracking and can be considered as sustainable and environment friendly solution for durability and resistance to frost weather.
Key words: Bacteria, Durability, Concrete, Freezing and Thawing, Strength properties.