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Experimental and Analytical Investigation of Air-Entrained Slag-Based Geopolymer Concrete under Freeze-Thaw Conditions

Afshar, Bahareh | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57177 (09)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Toufigh, Vahab
  7. Abstract:
  8. In cold climates, structures are exposed to low temperatures during winter, which is one of the primary factors contributing to the deterioration of mortar and concrete. The destructive effect of freeze-thaw cycles on concrete is the main cause of concrete failure in cold regions. Frost damage in concrete is a complex physical phenomenon that begins with the internal microstructure of concrete. This damage occurs when water fills the voids of porous material and then freezes and expands. A prerequisite for improving the resistance to frost and extending the useful life of concrete is understanding the damage mechanism and the performance evolution model in a thawing and freezing environment. On the other hand, geopolymers are an excellent alternative to conventional Portland cement, significantly reducing greenhouse gas emissions and energy consumption. This research focuses on the effects of processing conditions on the melt and freeze resistance of geopolymer concretes containing blast furnace slag and perlite encapsulating material. The strength of geopolymer concrete depends on the composition of the materials mixed together. In the production of geopolymer concrete in this project, two different grades of slag (450 and 400 kg/m^3), two different water-to-slag ratios (0.35 and 0.4), and sodium hydroxide and sodium silicate activators were used. Geopolymer composites have excellent mechanical performance and a shorter setting time compared to cement materials. The tested concretes were processed for 28 days in three humid environments: in water and at a temperature of 70 degrees Celsius. According to ASTM C666 standard, the samples were subjected to 150 freeze-thaw cycles in the temperature range between 4°C and -18°C. The change in weight and appearance, compressive strength, and dynamic modulus of elasticity of these samples were investigated. Through non-linear analysis of waves, three inherent wave characteristics were extracted to study the relationship between these characteristics and the behavior of concrete. The experimental results showed that after 150 cycles, in terms of mechanical performance, curing conditions in water and in a humid environment are better than thermal curing conditions for geopolymer concretes. Conventional concrete with thermal treatment conditions was completely destroyed after 100 cycles based on the reduction of relative elasticity modulus. The lowest reduction in compressive strength is 2.74% for concrete with a grade of 400 kg/m^3 and a water-to-slag ratio of 0.35 under water treatment, while the highest reduction in compressive strength is 35% for normal concrete under thermal treatment. The samples treated in water had the least decrease in compressive strength, whereas the heat-treated samples had the highest decrease in compressive strength. Furthermore, the lowest mass loss of the samples is 0.62% for concrete with a grade of 400 kg/m^3 and a water-to-slag ratio of 0.4 under water treatment. Also, the highest mass loss is 7.76% for normal concrete under thermal treatment. By examining the peak-to-peak parameter, energy, and second harmonic of the features extracted from the non-destructive evaluation, the most degradation is related to the thermal treatment conditions
  9. Keywords:
  10. Geopolymer Concrete ; Freeze and Thaw Cycles ; Grand Granulated Blast Slag ; Ultrasonic Waves ; Pearlite

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