Casting Method Development and Characteristics Enhancement of High Performance Concrete by Utilization of Nano-SiO2 Particles and Different Types of Fibers

Mobini, Mohammad Hossein | 2016

471 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 48655 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Khaloo, Alireza
  7. Abstract:
  8. The aim of this study was to evaluate the effects of applying low replacement ratios (0.75% and 1.50% of the binder weight) of nano-SiO2 particles with different specific surface areas (200 and 380 m2/g) on the properties of high-performance concrete (HPC). Mechanical (compressive and splitting tensile strengths), electrical resistivity, non-destructive (ultrasonic pulse velocity), and microstructural (mercury intrusion porosimetry, X-ray diffraction, and scanning electron microscopy) tests were conducted to investigate the macroscopic and microscopic effects of nano-SiO2 particles on HPC characteristics. The results indicated that the performance of nano-SiO2 particles significantly depended on their specific surface areas and the water to binder (w/b) ratio of the mixtures. By decreasing the HPC w/b ratio from 0.35 to 0.25, nano-SiO2 particles with lower specific surface area performed better than finer one (higher specific surface area). Microstructural investigations demonstrated that the decrease in efficiency of nano-SiO2 particles with higher specific surface area at lower w/b ratio correlates to the formation of nanoparticles agglomerates, particularly at the higher replacement ratio of nanosilica (1.5%). However, the influence on the compressive and splitting tensile strengths and electrical resistivity varied due to differences in performance of nano-SiO2 particles affected the mechanical and durability properties.
    Moreover, in the present study, the effect of pyrogenic nanosilica with different specific surfaces areas (200 and 380 m2/g) on mechanical properties of fiber-reinforced high-performance concrete (FRHPC) produced with two different types of fibers including steel and polypropylene fibers was investigated. Accordingly, different mechanical tests (compressive, splitting tensile and flexural strengths) as well as electrical resistivity were performed at 7, 28, and 91 curing days. In addition, the modulus of rupture and flexural toughness of FRHPC prisms were calculated based on the flexural testing results. Also, scanning electron microscopy test (SEM) was conducted to evaluate the microstructural performance of pyrogenic nanosilicas in the matrices of FRHPCs. Results demonstrated that the application of pyrogenic nanosilica can enhance the mechanical and electrical resistivity properties of FRHPC. In addition, the coarser type of pyrogenic nanosilica showed better performance in increasing the mechanical properties of FRHPC than finer one. However, the finer type of pyrogenic nanosilica resulted in higher electrical resistivity in FRHPC specimens compared to coarser nanosilica. Moreover, according to SEM test, the enhancement of mechanical properties of FRHPC in the presence of pyrogenic nanosilicas could be related to the densification of the matrix caused by their particles
  9. Keywords:
  10. High Performance Concrete ; Mechanical Properties ; Steel Fibers ; Polypropylene ; Nanosilica ; Electrical Resistivity ; Nondestructive Test ; Microstructure

 Digital Object List