The Post-fire Behavior of Lightweight Structural Concrete is Improved by Nano-SiO2 and Steel Fibers

The primary goal of the engineering design of building is to reduce the weight of the structure and its resistance to fires and earthquakes because fires are inevitable. Hence, the direction of this study was to use lightweight concrete because of its unique advantages in weight loss and fire resistance due to its thermal insulation property. It was also intended to enhance the strength and behavior of this concrete at high temperatures. For this purpose, four mixing designs  samples without fibers and nano-SiO2, samples with different proportions of nano-SiO2, samples with different proportions of fibers, and samples with both fibers and nano- SiO2 together were prepared. The results showed damage to samples free of nano-SiO2 and fibers, changing their color, reducing their resistance and reducing their weight. But adding nano-SiO2 fibers or using them together leads to improving the properties of concrete at all temperatures. Due to nano- SiO2, its pozzolanic interactions improve the microstructure, and the fibers prevent cracks in concrete. This study also dealt with the effect of changing the size of the samples on the compressive strength, and the results showed an increase in the resistance of the samples with small sizes, and resulted factors for converting the resistance of non-standard samples into a standard.