Mechanical and Durability Properties of Paste, Mortar and Concrete Incorporating Nano-Silica and Nano-Alumina as Nanomaterials using Ordinary Portland Cement and Alkali Activated Concrete

Abstract

Nanotechnology has many applications in civil engineering, especially in concrete. Nano silica and nano-alumina can improve the strength and durability properties of concrete and mortar. They reacts with Ca(OH)2 formed during the hydration process produced additional C-S-H, which is the main constituent for enhancing the mechanical properties of concrete. This study investigates the effects of nano-silica and nano-alumina on the mechanical properties of paste, mortar, and concrete. 1%, 2%, 3% and 5% nano-silica and 1%, 2%, and 3% nano-alumina were used as cement replacement. Mechanical properties like compressive strength, flexural strength, split tensile strength, Modulus of Elasticity and setting time of different mixes were evaluated and compared with ordinary Concrete. The results showed that compressive strength was increased with the addition of nanomaterial up to 3%. Nano silica when used as 3% of replacement of cement, it was observed that the 28-days compressive strength of mortar was higher than control mortar by 28%. Higher than 3% of nano-silica will lead to a decrease in compressive strength. Similarly, in concrete with ordinary cement and alkali activated concrete (AAC), the inclusion of 3% nano-silica in OPC and AAC concrete led to increase in 28 day compressive strength by 20% and 14%, respectively. Inclusion of 1% nano-alumina in mortar led to 14% increase in compressive strength at 28-days strength. Concrete with 2% dosage of nano-alumina had 15% and 10% increase in compressive strength at compared to concrete without nano materials. Flexural strength and split tensile strength of both the types of concrete with 3% nano-silica and 2% nano-alumina shows the maximum results. There was no significant change in the modulus of elasticity of concrete due to the incorporation of nano-silica and nano-alumina. For 3% of nanosilica, it was observed that the 28-days compressive strength of high strength concrete was higher than control high strength by 18%. Rapid chloride permeability test, chloride attack and sulphate attack tests were performed to observed durability properties of ordinary concrete and alkali activated concrete. In terms of chloride permeability, the best results were obtained with the 3% nano-silica and 2% nano-alumina. Due to chloride attack compressive strength was decreased by 1.75% to 6% after 28 days of immersion. Sulphate attack lead to dissolution of hydration products like portlandite and formed gypsum and ettringite which reduced the strength of concrete. 3% nano-silica and 2% nano-alumina shows the maximum positive results during the chloride and sulphate attack tests.