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The use of nanotechnology is of prominent research interest in the construction industry. Introducing nanomaterials into cementitious systems enhances its characteristic material properties. Nano-silica is the most efficient nanomaterial in replacing cement without compromising its strength and durability. Nano-silica also enhances the properties of cement when in conjugation with other supplementary cementitious materials. Nano-silica offers high chemical reactivity and introduces filler effect in the cement matrix, thereby densifying the interfacial transition zone (ITZ) and improving the properties of cement-based materials. However, the addition of nano-silica more than the optimum dosage reduces the strength and durability. Apart from the dosage, many other parameters also influence the properties of nano-slica blended cement composites. This study deals with the changes in characteristic properties of cement and cement-based materials upon incorporation of nano-silica.

Extensive studies have been reported on the development of service-life prediction of reinforced concrete structures in the last two decades. Service life of a reinforced concrete structure is dependent on the corrosion process, specifically chloride threshold value. Chloride threshold value is a distinctive property and is dependent on several factors such as the supplementary cementitious material used, presence of surface cracks, water to binder ratio, type of steel reinforcement, exposure conditions, measurement methods, etc. Although chloride threshold value is an influential parameter in service-life prediction, a definitive chloride threshold value considering these factors is not reported in the existing literature and standards. Moreover, values adopted in many analytical tools for service life predictions based on the type of steel reinforcement alone are not appropriate and leads to inaccurate calculations. There is a gap in the available literature in understanding the selection of suitable chloride threshold values to be adopted for a specific system. Therefore, it is imperative to study the variation of chloride threshold value with exposure conditions as well as other influencing parameters, to achieve proper service life prediction. In the paper, several influencing parameters on chloride threshold value and its significance on prediction method are comprehensively reviewed. Moreover, suitable recommendations are highlighted for Indian and international standards at the later part of the study.