Sharif Digital Repository

Failure of concrete structures is usually accompanied by expansion of interior cracks due to stress concentration at the cracks tip. This phenomenon shows the importance of examination of the failure behavior of concrete structures. For this purpose, 4 types of concrete samples with different amounts of nano-SiO2 (0%, 0.2%, 0.5%, and 0.8%) were made to prepare some Central Straight-through Crack Brazilian Disk (CSCBD) specimens. The key focus of the investigation conducted was to investigate two assumptions. First, to check the pure mode I (tension) and pure mode II (shear) by compressing the standard discs with central cracks by an angle of 0° and 27° with respect to the loading axis;... 

Wettability alteration in porous media is one of the mechanisms for enhancing oil recovery through injecting low-salinity water into carbonate reservoirs, in which active ions can remove the carboxylic oil component from the rock surface, altering the rock's wettability toward a water-wet condition. This study investigated the concomitant effects of low-salinity water and hydrophilic SiO2 nanoparticles on oil-wet dolomite rock. Results revealed that low-salinity water coupled with hydrophilic nano-SiO2 in oil-wet dolomite rock remarkably affected the wettability alteration of the rock, showing that the simultaneous presence of ions in water and hydrophilic nano-SiO2 led to considerable... 

The high hydration potential of CaO and MgO phases restricted the application of Mag-Dol refractory composites. In this study, the impact of nano-silica (SiO2) addition on the physical, mechanical, thermo-mechanical as well as microstructure of Mag-Dol refractory composites is investigated. Mag-Dol compositions were prepared by using calcined dolomite and magnesite particles (micron, 0–1, 1–3, 3–5, and 5–8 mm), liquid resin, and 0, 0.5, 1, 1.5, 2, and 2.5 wt% nano SiO2 as additives. Specimens were heated up to 1650 °C for the 3 h soaking period. Fired specimens were characterized by physical (apparent porosity, bulk density, and hydration resistance), mechanical (cold crushing strength), and... 

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... 

In the present research, the influence of nanodiamond (ND) and a physical hybrid of ND and fumed nano-SiO2 were investigated on the performance of a typical tire tread compound. The styrene-butadiene rubber (SBR) and cis-butadiene rubber (BR) blend filled with a commercial grade highly dispersive silica at 70 phr loading were used as typical tire tread compound. ND was substituted partially with silica at two different concentrations of 5 and 10phr. Meanwhile, 5 phr of ND/nano-SiO2 hybrids with the weight ratio of 2.5/2.5 and 1/4 were substituted with silica. ND-Filled compounds exhibit increased scorch and cure time compared to controls. Improvement in different characteristics of the...