The effect of nanomaterials on properties of geopolymers derived from industrial by-products: A state-of-the-art review

Nanomaterials, owing to their extraordinary properties are known to improve the microstructure of concrete, enhances the fresh and hardened properties of cement concrete, are widely used in cementitious materials. Many studies have been conducted so far to understand the effects of inclusion of nanomaterials on the geopolymerisation reaction, fresh and hardened state properties, microstructure, and durability of geopolymer composites. The current paper summarizes these studies mainly focusing on the effects of various nanomaterials such as nano-SiO2, nano-Al2O3, nano-TiO2, carbon nanotubes and nano-clay on geopolymer paste, mortar and concrete derived from various industrial by-products as sources of aluminosilicates. Most of the geopolymer products revealed that nanomaterials enhance the fresh and hardened state properties if used in a controlled quantity. Nano-silica and nano clay inclusion up to 2% by weight significantly enhances the rate of geopolymerisation reaction, reduces the setting times and improves the hardened state properties. Carbon nanotubes and nano-TiO2 enhances geopolymerisation by offering additional nucleation sites. Nano-alumina more prominently reduces the porosity but lesser effective in geopolymerisation. X-ray diffraction studies report the increase in XRD peaks indicating the formation of additional hydration products that comply with SEM studies. Investigation of SEM and FTIR reveals that the inclusion of nanomaterials densify the microstructure of geopolymer composites and produce high mechanical strength. Durability studies reveal that enhanced geopolymerisation with nanomaterials also prevents interconnectivity of micropores due to the formation of a denser matrix of geopolymer gel. The possible health-related issues associated with the use of nanomaterials has also been identified. The cost effectiveness of using nanomaterials is also discussed. (C) 2020 Elsevier Ltd. All rights reserved.