Recycling of Nano Silica Waste from Aluminum Fluoride Industry in Cement Mortar

The application of nanotechnology in cement mortar has added a new dimension to improving the mechanical performance of cementitious materials. Huge amounts of waste silica generated as a byproduct from aluminum fluoride industries poses heavy economic and environmental challenges. The objective of this study is to investigate the effect of replacement of cement with waste nano-silicas (NS) on the characteristics of cement mortar mainly the compressive strength, flexural strength, workability, density, and heat of hydration. Cement was replaced with NS with percentage of (0.5,1,1.5,2,2.5%, 4, 6, 8, 10%), with a constant water-to-cement ratio (C/W) of 0.5. Depending on the obtained results, it has been observed that substitution of cement with NS has insignificant adverse impact on the characteristic of the mixture at low content of NS. Slight decrease (5.5%) in the compressive strength occurred at 7 days at low substitution percentage (0.5%), and 11.5% at 28 days. Flexure strength decreased by 23% and 55%, workability increased slightly by 1.33% and 6.8% at substitution percentage of 0.5%, and 2.5% respectively. Also, substitution resulted in significant reduction in the mortar weight up to 18.49% at substitution percentage of 10%, while insignificant impact on the hydration rate was observed for all substitution percentages. It can be concluded that recycling of waste NS in cement mortar mixture provided an attractive option to reduce the impact of waste on the environment, reduce cement consumption, reduce concrete weight, conserve natural resources and save the environment.