An Investigation of the Effect of Nano–Silica on Freeze and Thaw Using poumic in lightweight-Concrete in Sulfate Environment

Khoshbakht, Mehrdad and Mohammadi, Yaghoub (2018) An Investigation of the Effect of Nano–Silica on Freeze and Thaw Using poumic in lightweight-Concrete in Sulfate Environment. Masters thesis, University of Mohaghegh Ardabili.

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Abstract

Research Aim:Unlike natural perseverance of concrete, there are so many concrete structures that don’t show effective properties against cold and drastic weather. One of the most important reason of demolition of concrete in cold region of Iran emanate from freeze and thaw cycles of concrete. Strength of concrete against freeze and thaw cycles depends and high stress on concrete, especially when water of aggregates becomes solid and alters volume of concrete in cold weather. This change in volume creates fine cracks in concrete that finally cause decline in strength and invited numerous investigations. Research method: In this study effect of nano silica (1%, 2% and 3%) and poumic(0%, 0. 2%, 0. 4%, 0. 6%, 0. 8 and 1) replaced with aggregate in phases of control samples and cycle samples in sulfate environment for increasing compressive strength and other mechanical properties of concrete has investigated. Totally 432 samples were created that 288 of them were under freeze and thaw action based on ASTM (C666 B) code, after 45 cycles, 100 cycles and 150 cycles, and the remaining 144 samples as a control samples in 7, 14, 28 and 90 ages were gauged. Compressive strength, ultrasonic testing (dynamic modulus of elasticity) and losing weight of samples after freeze and thaw cycles were considered as perseverance criteria of concrete. Findings:In consideration mixture of nano-silica with poumic the highest compressive strength were attained for 1% nano-silica with 0.8% poumic. Conclusion: The most important problem with working with reinforced concrete to nano-silicon is to lower the performance of concrete, which in order to overcome it, it is necessary to add a suitable super-lubricant to the mixture. The use of more than 2% of powdered nano-silica does not only increase the mechanical properties of concrete, but also reduce its loss in ordinary samples and its loss in samples exposed to melting and freezing cycles; therefore, the consumption of more than 2% powder nano silica in concrete is not recommended.

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