Browsing by Author "Nikraz, Hamid"

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    Corrosion of Low Calcium Fly Ash Geopolymer Concrete: a Preliminary Study
    (2013-06-04) Olivia, Monita; Nikraz, Hamid
    A study of the durability of geopolymer concrete is a step forward in ensuring this material’s technical viability. Geopolymer concrete from low calcium fly ash was reported to have a good resistance in aggressive environments, such as acid and sulfate. This research presents a preliminary study of the corrosion resistance of low calcium fly ash geopolymer concrete. The resistance of geopolymer concrete against damage caused by corrosion of steel reinforcement has been investigated using an accelerated impressed voltage setup in 4% sodium chloride solution. The chloride resistance, water absorption and sorptivity of the concrete were also determined. An SEM investigation of geopolymer microstructure was also presented. The results of the test indicated that the geopolymer concrete has a good resistance to corrosion in a chloride solution environment.
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    Corrosion Performance of Embedded Steel in Fly Ash Geopolymer Concrete by Impressed Voltage Method
    (2013-06-04) Olivia, Monita; Nikraz, Hamid
    The present paper covers a study of the corrosion performance of embedded steel in fly ash geopolymer concrete by an accelerated corrosion test set up. Concrete specimens were exposed to a constant impressed voltage of 5V and 30V. Two optimized fly ash geopolymer concrete mixtures were compared with a control mix (OPC concrete) at an equivalent strength grade. Alkalinity reduction by phenolphthalein spray, chloride penetration by AgNO3 spray and half cell potential measurement were also investigated. The accelerated corrosion test was carried out for 28 days. Results indicate that the geopolymer concrete displayed a smaller recorded current and higher electrical resistance than the corresponding control mix. Small cracks were observed in the fly ash geopolymer samples. It can be concluded that the fly ash geopolymer concrete had good corrosion performance and yielded longer time to failure than the OPC concrete.
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    Durability of Low Calcium Fly Ash Geopolymer Concrete in Chloride Solution
    (2013-06-04) Olivia, Monita; Nikraz, Hamid
    This paper describes a durability study of low calcium fly ash geopolymer concrete under an accelerated wetting drying testing. The main parameters were aggregate content, alkaline/fly ash ratio, ratio of sodium silicate/sodium hydroxide and curing conditions. The accelerated test method was carried out by subjecting the geopolymer concrete to repeated cycles of chloride solution immersion and oven drying. The specimens were immersed in 6.54% chloride solution for 24 hours and were heated at 800C for 24 hours. Physical properties such as a change in mass and compressive strength were monitored. The results indicate that the geopolymer concrete has a good resistance on the accelerated wetting drying cycles. The compressive strength of the exposed concrete increased about 16-33% after the wet-dry cycl
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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.
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    Strength and water penetrability of fly ash geopolymer concrete
    (2013-06-04) Olivia, Monita; Nikraz, Hamid
    This paper presents a study on the strength development, water absorption and water permeability of low calcium fly ash geopolymer concrete. Geopolymer mixtures with variations of water/binder ratio, aggregate/binder ratio, aggregate grading, and alkaline/fly ash ratio were investigated. OPC (Ordinary Portland Cement) concrete with the same strength level was used as a control mix. Strength was measured by compressive strength, while water penetrability was evaluated by water absorption and water permeability. In addition, the AVPV (Apparent Volume of Permeable Voids) was measured. The results show that the strength of fly ash geopolymer concrete was increased by reducing the water/binder and aggregate/binder ratios; and the water absorption of low calcium fly ash geopolymer was improved by decreasing the water/binder ratio, increasing the fly ash content, and using a well-graded aggregate. There was no significant change in water permeability coefficient for the geopolymer with different parameters. The test data indicates that a good quality of low calcium fly ash geopolymer concrete can be produced with appropriate parameterisation and mix design.
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    Water Penetrability of Low Calcium Fly Ash Geopolymer Concrete
    (wahyu sari yeni, 2013-06-04) Olivia, Monita; Nikraz, Hamid
    This paper presents a study on water penetrability properties, namely water absorption, volume of permeable voids, permeability and sorptivity of low calcium fly ash geopolymer concrete. In this research, geopolymer concrete is made from fly ash with a combination of sodium hydroxide and sodium silicate as alkaline activator. Seven mixes were cast in 100x200mm cylinders and cured for 24 hours at 600C in the steam curing chamber. After 28 days, the cylinders were cut into slices for permeability, sorptivity and volume of permeable voids tests. In addition, a microstructure characteristic of geopolymer concrete was studied using Scanning Electron Microscopy (SEM). Results indicate that geopolymer concrete has low water absorption, volume of permeable voids and sorptivity. It is found that the geopolymer concrete could be classified as a concrete with an average quality according to water permeability value. Moreover, a low water/binder ratio and a well-graded aggregate are some important factors to achieve low water penetrability of geopolymer concrete.