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Investigation of the tensile and fracturing behaviour of geopolymer concrete made by sodium hydroxide activation of gold mine tailings
Khan, Ammad
Khan, Ammad
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2021
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Geopolymerization is the process of alkali activation of alumino-silicates in raw materials to make construction materials. Industrial wastes like fly ash and blast furnace slag and mining industry wastes such as mine tailings in form of crushed rocks are commonly used raw material for production of geopolymers. Geopolymerized mine tailings have a wide application in building and construction industry. The compressive strength of geopolymer has been extensively studied by many researchers; however, the tensile strength remains largely unexplored. Understanding of tensile behavior and fracture mechanics of geopolymerized tailings is critical and established techniques by the rock mechanics community such as the direct and indirect tensile tests can be utilized for evaluation of the material’s behavior. Different indirect tensile test methods such as splitting tensile strength, three- and four- point bending, and semi-circular bend test have been used. The research objectives of this study were to evaluate the splitting tensile strength and flexural strength of the geopolymer concrete, identify critical strain levels for crack initiation, determine the mode I fracture toughness of the material, and ascertain the critical strain energy release rate. In this study, the splitting tensile strength of alkali activated geopolymerized mine tailings was investigated using the Brazilian indirect tensile method and the flexural strength has been investigated using semi-circular bend (SCB) test along with the digital image correlation (DIC) technique. A novel experimental set up was developed to perform the tests for this new type of material. For specimen preparation, sodium hydroxide (NaOH) was used as the alkali activator with molar concentrations of 8M, 10M and 12M. Initial water/tailing ratio was kept as 20% and specimens were tested after 7, 14 and 28 days of curing. All the specimens were kept in oven at 75°C for an initial 24 hours and then sealed and cured at room temperature. Prior to the testing, the specimen was placed in the oven at 75°C for 24 hours to reach the dry condition. For SCB test, the semi-circular specimen were prepared with notch as well as without notch. SCB specimen without notch was used to ascertain the flexural strength of the specimen and SCB specimen with notch were used to characterize the fracturing behavior of the material. The length of the notch to the radius (a/R) of the specimen varied from 0.2 to 0.3. The results indicate that splitting tensile strength of the specimen increased with the increase in molar concentration of NaOH. For 12M specimens the splitting strength was 1.8MPa. Generally, the tensile strength remained within the range of 10 to 12 % of the compressive strength of the geopolymer. The average flexural strength of the specimen was 1.7MPa for 10 M concentration of the specimen. The average mode I fracture toughness of the material was 0.2 MPa√m. The critical energy release rate, the measure of decrease in potential energy due to the increase in fracture surface area was estimated to be 32.2 N/m. The results from DIC analysis were compared with the extensometer physically attached at the bottom of the specimen to measure crack mouth opening displacement and both results were comparable.
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