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Compressive, tensile, and flexural strength of cement mortar containing 1, 3, and 5 wt% of aluminum oxide (Al^sub 2^O^sub 3^) nanoparticles were investigated. Samples containing 1 and 3 wt% Al^sub 2^O^sub 3^ nanoparticles show better mechanical properties than ordinary cement mortar. Increasing Al^sub 2^O^sub 3^ nanoparticles more than 5 wt% reduces the mechanical strength.
Mineral additions are used for improving the performance of cement-based mortar. In recent years, the use of nanoparticles, especially silica nanoparticles, has increased due to their small size, high specific surface area, and high activity. It has been shown that adding silicon dioxide (Si02) nanoparticles to hardened cement paste increases the compressive strength and bonding strength of the paste-aggregate interface more than the addition of silica fume. Also, it is reported that the addition of Si02 nanoparticles improves the microstructure of the cement and increases freezing resistance in high-performance concrete.1*2
More study has been conducted on the effect of adding Si02 particles with different diameters and in different amounts to the cement mortar. Samples containing large-diameter silica nanoparticles had improved mechanical properties. This is related to the possibility of agglomeration of smaller-diameter nanoparticles.3
Some of the studies focused on the comparison between the effects of adding different kinds of nanoparticles. For example, research on the addition of titanium dioxide (Ti02) and Si02 nanoparticles shows that the abrasion resistance and flexural fatigue performance of concrete containing Ti02 is more abrasion resistant than concrete containing the same amount of Si02 nanoparticles. Concrete containing Ti02 is also more resistant to chloride penetration than the concrete containing the same amount of SiO.
There are some studies on the effect of adding aluminum oxide (A1203) nanoparticles to cementing materials. One focused on the effect of A1203 nanoparticles on mechanical properties and percentage of water absorption of concrete that was cured in water and saturated limewater. Results show that adding nanoparticles up to 2 wt% improves the mechanical properties and concrete penetration, which is considerably more than the amount of mechanical properties achieved for the samples cured in limewater.710 The goal of this study was to evaluate the effect of adding A1203 nanoparticles to cement mortar, obtain the optimized weight percentage of nanoparticles, and present a desirable mechanism to improve the mechanical properties of cement mortar.