Fire is one of the serious threats that any concrete structure can face in its lifetime (Wasim and Hammad, 2015). The damage caused by fire is vast not only to the environment but also to life and property (Ulrich, 1988; Rashad, 2015). Though concrete can sustain high temperatures their failure pattern is unpredictable leading to a catastrophe (Nima et al, 2013; Chan et al, 2000). The durability studies of concrete also consider fire study as an integral part of their study (Ali et al, 2020). The prolonged exposure to heat weakens the integrity of concrete and thus makes them fail all of a sudden (Mohamed Salhi et al, 2020). In addition these are some concrete structures that are always subjected to temperatures higher than that intended for namely refractory and nuclear purpose concretes (Yanfeng et al, 2008). They can undergo various physical and chemical changes during their lifetime and hence their temperature stability has to be assessed before they can be used in field applications (Hanaa et al, 2009). Well developed hydration phases can make the concretes thermally stable (Nuruzzaman et al, 2020). The use of thermally stable aggregates can also contribute to the volume stability of concrete even at higher temperatures. The use of alternative sand should meet the design and ecological requirements as well as must possess thermal stability. One such material is zircon sand that are available plenty in nature occurring along the ancient coastlines (Umarajyadav and Vahini, 2017). They are highly stable to high temperatures and are also chemically inert (Richard et al, 2004). The chemical and thermal stability of the zircon sand makes them a widely used material for use in thermal applications and foundry (Rand et al, 2018). The use of zircon sand as fine aggregates shall provide a solution for reducing the demand on natural river aggregates as well as meeting the thermal requirements of aggregates (Renisha et al, 2019).
Though self compacting concrete is a universally accepted material they also possess several disadvantages such as presence of voids and pores which forms channels for the ingress of harmful ingredients into concrete due to the lack of any external vibration techniques (Hossein and Farhad, 2020). Generally self compacting concrete is used as filling agents for reinforced concrete structures and hence any formation of micro cracks causes the penetration of CO2, chlorides and moistures weakening the structure of the concrete (Brahim Safi et al, 2013). The concrete reinforced using steel is not highly resistant towards such deleterious substances. Therefore to minimize the risk caused to the reinforcements, the usage of ultra fine and nano materials for the design self compacting concrete becomes an inevitable choice (Zapata et al, 2013). The properties of the self compacting concrete mainly depend on the mortar phase and hence study if mortar properties explain the concrete behaviour (Tung-Chai Ling et al, 2012). Nano mortar is a general term used for the mortar containing nano material as an additive (Zhan et al, 2019). The bulk properties of concrete are significantly improved by the inclusion of nano sized particles in concrete through improvement in packing capacity (Zhenhua et al, 2006). The micro pores of concretes are reduced to nano scale and nano pores are completely nullified due to nano material addition (Shaikh et al, 2014; Nazari and Riahi, 2011). The drawbacks found in concrete such as permeability, porosity and alkali silica reaction are also found to reduce due to the nano material addition (Singh et al, 2013; Muhd Norhasri et al, 2017). Hence more durable and enhanced concrete performance can be attained through the filling capacity of nano particles and also through their involvement in the chemical hydration reaction (Sobolev and Ferrada Gutierrez, 2005). Since the emergence of nano technology, several nano sized particles have been produced by limiting their size to nano levels without affecting their original chemical composition and physical properties (Rahmat et al, 2015). Nano materials have already been used in self compacting mortars for the past decades to yield sufficient strength and stability (Ehsan et al, 2015). Highly innovative materials have been used in concrete that are of micro and nano scale have yielded good thermal stability and mechanical strength of the mortar (Nestor et al, 2014). Comparatively the use of nano size materials has yielded much more positive results than the micro particles (Berra et al, 2012). Use of nano materials as replacement or additive to cement also involves several technological implications (Elzbieta et al, 2017). The proper dispersion of nano materials in cement should be taken utmost care otherwise which could lead to negative consequences. The proportion of nano materials required to produce high quality concrete system also needs to be assessed before they can be incorporated in concrete system (Deyu Kong et al, 2012).
This research work mainly aims at utilization of zircon sand in self compacting mortar with the combined effect of nano-silica and nano alumina as additive for cement. Despite several studies on self compacting mortar, no study has been attempted to characterize the combined effects of adding nano silica and nano alumina on the properties of self compacting mortars with zircon sand aggregates have also not been studied so far. The study is an initiative to create confidence on the use of zircon sand as an ingredient for the production of self compacting mortars. The research also tries to harness the thermal stability of zircon sand to improve the fire resistant behaviour of self compacting mortars.