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The Effect of Adding Pozzolans on the Mechanical Properties of Latex-Modified Concretes and Investigating the Separation of Fibers in Them

Tohidloo, Mohammad | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56764 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Khalu, Alireza
  7. Abstract:
  8. This research investigates the impact of a new type of latex called Carboxylated Styrene Butadiene Rubber (XSBR) on the mechanical properties and permeability of latex-modified concrete. Latex-modified concretes offer numerous advantages, but a key challenge is the reduction in compressive strength, hindering their widespread use, especially in structural applications. In the initial phase of this study, the influence of XSBR latex is examined, and four different dosages of XSBR latex are incorporated into concrete. Keeping other parameters constant, especially the water-to-cement ratio, a comparison is made between different mix designs. All specimens are subjected to two different curing conditions, combined and wet, to determine the optimal operational conditions for XSBR latex-modified concrete. The results indicate that XSBR latex-modified concrete performs significantly better under combined curing conditions. Using XSBR latex in proportions less than 15% in combined curing and less than 10% in wet curing can increase compressive strength. For instance, adding 5% latex in combined curing enhances the 28-day compressive strength by 39.2%. The use of latex alters the microstructure of the concrete, creating a three-dimensional sponge-like network and reducing permeability, tensile strength, and abrasion resistance. Finally, the study suggests an optimal latex percentage of approximately 5 to 10% by weight of cement in concrete, considering the intended application. In the second part of the research, the use of microsilica as a pozzolan in XSBR latex-modified concrete is explored to achieve higher compressive strength. Microsilica is substituted for cement in four different percentages (7.5%, 10%, 12.5%, and 15%), and an additional mix design with 10% microsilica surplus in XSBR latex-modified concrete is created to investigate the effects on the water-to-cement ratio. The replacement of 10% of cement with microsilica yields better results compared to other formulations, enhancing both compressive strength and abrasion resistance. However, the permeability of XSBR latex-modified concrete increases when microsilica is used, which is an undesirable outcome. In the third part, polypropylene fibers are introduced at a volume fraction of 0.1% in XSBR latex-modified concrete to assess their compatibility with this type of latex. As repeated abrasions are one of the primary causes of damage to concrete, the addition of polypropylene fibers increases both abrasion resistance and tensile strength. However, other parameters are weakened, and the overall results are not favorable. Therefore, the use of polypropylene fibers in XSBR latex-modified concrete is not recommended
  9. Keywords:
  10. Polypropylene ; Mechanical Properties ; Microsilica Pozzolan ; Polymer-Modified Concrete ; Latex-Modified Concrete ; Carboxylated Styrene Butadiene Rubber (XSBR) ; Repair Concrete

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