Browsing by Author "Javaherdashti, Reza"

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    The influence of micro algae on corrosion of steel in fly ash geopolymer concrete: a preliminary study
    (2013-06-04) Olivia, Monita; Moheimani, Navid; Javaherdashti, Reza; Nikraz, Hamid; Borowitzka, Michael
    Chloride is not the only main cause of corrosion of reinforced concrete structures in seawater environment. Microorganisms, such as bacteria and microalgae, in the seawater can induce microbiologically influenced corrosion (MIC) that leads to degradation of the concrete structures by formation of biofilm on the metallic surface. In this preliminary study, the impact of microalgae on the corrosion of steel reinforced bars in fly ash geopolymer concrete was studied. Corrosion potential, algae cells number, and pH measurement were carried out for fly ash geopolymer concrete and a control mix (Ordinary Portland Cement) samples. The results indicate that the corrosion potential of fly ash geopolymer concrete was influenced by the cathodic reaction during photosynthesis activities. The geopolymer concrete in algae-inoculated medium was found to be more tolerant to algal growth than the control mix (OPC concrete). There was a positive correlation between algae cell densities and the potential reading of the geopolymer
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    On the impact of algae on accelerating the biodeterioration/biocorrosion of reinforced concrete: a mechanistic review
    (2013-06-04) Javaherdashti, Reza; Nikraz, Hamid; Borowitzka, Michael; Moheimani, Navid; Olivia, Monita
    In this paper, the complexities involved in both microbiologically influenced corrosion and deterioration of reinforced concrete structures by algae are explained. In this regards, the five possible corrosion/deterioration mechanisms that may be expected are addressed and described. These mechanisms are as follows: • Absorption of some chemicals necessary for the algae from within the cement paste of the concrete: this mechanism can finally result in drying out the concrete and developing cracks as a result of formation of internal cavities and voids. • Biofilm formation and increasing the likelihood of attracting more micro-/macroorganisms that can either deteriorate the concrete itself or the reinforcement steel inside , or both. An example as such can be development of an environment favorable for the acid-producing sulphur oxidizing bacteria that through generating very acidic conditions are capable of doing harm to both metallic and non-metallic phases of the reinforced concrete. • Development of electrochemical cells such as differential aeration cells due to the photosynthetic driven oxygen production and consumption features of algae. In On the Impact of Algae on Accelerating the Biodeterioration/Biocorrosion of Reinforced Concrete: A Mechanistic Review 395 this way, it is likely that spots of varying oxygen partial pressures will be created, tus facilitating the corrosion of the steel inside. • Production of acids that can be detrimental to the mechanical integrity of both concrete and steel reinforcement. • Production of alkaline conditions that upon varying and fluctuating due to the chemistry of the system, can protect the concrete but do damage to the steel phase via mechanisms such as caustic embrittlement. The aim of this review paper is to gather all possible mechanisms that may be involved in explaining the contribution of algae to the bio-corrosion/bio-deterioration of reinforced concrete.