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128 Influence of bacteria on performance of air entrained concrete Niloofar parastegari n parastegari@cv iut ac ir January 14 2017 Department of Civil Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor Dr Davood Mostofinejad Prof Email address dmostofi@cc iut ac irAbstractConcrete is one of the most important construction materials due to availability high compressive strength andpasty state before setting However having high compressive strength is not enough for durability low tensilestrength of concrete will cause cracks on its surface Water and aggressive gases penetrate through cracks intothe concrete and lead to corrosion of the reinforcement To protect the concrete against cracks chemicalmethods epoxy or cement sand mortar as well as biotechnological methods calcium carbonate sedimentproduced by the bacteria are used In addition to being compatible with concrete biotechnological methodsare proved to be eco friendly Furthermore adding bacteria to the concrete during the construction repairs thecracks in the depth and at early ages The researchers have concluded that concrete and cement hydration is harmful to bacteria so bacteria must beprotected against dry environment and alkaline concrete One way of protection is to add air bubbles in theconcrete Bacteria is shielded in air bubbles where it can continue its activities The air bubbles also provideoxygen for feeding bacteria Therefore different percentages of air 5 8 and without intentionalproduction of air is used in this study Using six different mixing methods half of them containing Sporoscarcina pasteurii bacteria we investigatecompressive strength and electrical resistance 108 standard cylindrical specimens water absorption 36 cubicspecimens with dimensions of 70 mm steel corrosion 36 cubic specimens of 70mm with rebar the depth ofcarbonation 36 cubic specimens of 100mm survival in cycles of freezing and thawing 36 cubic specimenswith width and height of 100mm and length of 350mm impermeability 18 cubic specimens with length andwidth of 200mm and height of 120mm and accelerated chloride penetration 36 standard cylindricalspecimens of concrete We set concrete with three different percentages of air 5 8 and withoutintentional production of air using Sporoscarcina pasteurii bacteria the construction of half of them After thecuring period we performed surface restoration on some of the specimens randomly selected The results showed that calcium carbonate sentiment produced by bacteria fills the pores in concrete reduceswater absorption corrosion of rebar and depth of carbonation Furthermore it reduces weight changes insuccessive cycles of freezing and thawing Produced sediments restricted the free movement of ions in thepores of the concrete reduced chloride ion penetration and increased the electrical resistance Also calcium rich environment curing environment containing minerals improves bacteria s performance This results inincreased compressive strength and electrical resistance and reduced water absorption carbonation depth andpermeability to water under pressure Surface restoration generates a thin layer of calcium carbonate on the surface of concrete and limits thepermeability resulting in reduced penetration of chloride ions into the concrete interior which results in anincrease in its electrical resistance Presence of air bubbles in addition to bacteria decreases water absorption carbonation depth and chloridepenetration and dramatically increases electrical resistance In fact bacterial cells shielded by air bubbles fromalkaline concrete and dry environment show better performance Key wordsAir entrained concrete Bacteria curing condition Surface treatment Time

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