Construction industry is one of the biggest sectors globally and a wide variety of materials are used to carry out various works. Particularly, cement is a material that is used in the construction of various structures and it is also the major source of emission of CO2 gas into the atmosphere which results in global warming. Many researchers have identified various replacement materials for cement as a partial substitution and carried out experiments successfully. Nano silica is widely utilized as a partial replacement for cement and a lot of research is carried out. This paper reviews the past studies in which nano silica is utilized in various building materials such as cement mortars, normal concrete and special concretes. The fresh concrete properties, strength and durability of the material are the parameters reviewed and it is apparent that by incorporating nano silica in cement it absorbs more water, which makes the mix less workable and it imparts additional strength to the concrete and also provides better durability when compared with the control specimen. Hence it has been revealed that nano silica will be a good replacement for cement as it is pozzolanic in nature and also possessing good microstructure.
In this study, suitable fly ash (FA) was selected for agricultural purposes according to combined characteristic soils and water. The two FAs from the Tuticorin Thermal Power Plant (FA-TTPP) and Sripathy Thermal Power Station (FA-STPS) and physio-chemical analysis of soil and water samples from the five different sites (1–5) in Viruthunagar district, Tamilnadu is made. X-ray diffraction analysis (XRD) of FAs showed that quartz (SiO2), mullite (Al6Si2O), and hematite (Fe2O3) are available that enhance plant growth. The Fourier-transform infrared spectroscopy (FTIR) results confirmed that Si–O–Si, Al–O–Si, HO–OH, and OH bonding present in the FAs support to meet the required plant nutrients in the soil. Scanning electron microscopy analysis (SEM) of FA-TTPP revealed compact microspheres with regular, smooth, and irregular textures while FA-STPS showed glassy, unshaped fragments that may help to improve the texture of field sites. Energy dispersive X-ray spectroscopy (EDX) analysis found that FAs have essential macro- and micronutrients to minimize the soil nutrient and thus help to improve plant productivity. Sites 1 and 2 have acidic soil conditions and are recommended to use both FAs since they are alkaline in nature. FA can improve the water-holding capacity of sandy loam soils of sites 2, 3, and 4 due to the presence of fineness content in FA. Site- 1 has iron deficiency which can be remediated with rich iron FA-STPS. It is recommended to use optimum FA based on soil and water to improve agricultural efficiency.