(A review of the paper : Influence of nano - SiO2 on Portland cement pastes by M. Stefanidou and I. Papayianni)
*Corresponding Author : M. Stefanidou ; Email Address :email@example.com
The object of this review is to throw light on the paper : “Influence of nano- SiO2 on the Portland cement pastes” . This paper was written by M.Stefanidou and I. Papayianni. The paper is based on the research conducted by them on high strength cement pastes which were infused with nano-SiO2 at different percentages (0%, 0.5%, 1%, 2%, and 5%). These nano-SiO2 particles which were produced by pyrolysis have known to actually improve the properties of cement pastes thereby increasing their performance. From the research based on a number of tests , the authors came to the conclusion that the nano-SiO2 appear to affect the mechanical properties and the structure of high strength cement pastes even in minute concentrations. This research can therefore be considered as a continuation of testing nano particles in cement mixtures by increasing the packing factor or increase the hydration rate in the process of cement hydration.
Nano technology has contributed a number of materials that have excellent properties and a lot of research has been put into effect in order to create nano particles which could be infused into cement paste in order to improve their performance. The different stages of mechanical and structural properties were tested and research has been done in order to understand the influence of these nano particles over cement properties. Research done by testing micro silica or other materials often try to improve the hydration rate in cement hydration process. Quality of cement is enhanced by the addition of nano scale particles. SiO2, TiO2, Al2O3 and carbon nano tubes are the mainly used nano particles in cement products. Deformation and flow properties have been recorded in fresh mixture state while in hardened state compressive strength is improved. Sobolev et al.  reports increased initial strength in nano-modified mixtures which become reduced with age. Sobolev summarized it as : •Nano particles act as fillers in the empty spaces.
•Well distributed nano particles act as crystallization centres of hydrated products increasing hydration rate. •Nano particles assist towards the formation of small in size Ca(OH)2 crystals and homogeneous clusters of C-S-H composition. •Nano particles improve the structure of the transition zone between aggregates and paste.
Li  while testing cement with fly ash mentions that pozzolanic reaction of fly ash is improved when nano-SiO2 is added to the mixture.
The authors have focussed their research on the changes in micro structure of cement pastes after the addition of nano-SiO2 percentages. Tools like Scanning Electron Microscope, Transition Electron Microscopes have been utilized by them in identifying the changes in the nano modified pastes, while various mechanical and physical tests were conducted at different stages.
Methods adopted and their subsequent Data:
d(0.1) (µm)d(0.5) (µm)d(0.9)(µm)Density(g/ml)Surface area(m2/g) Cement 142.52.4514.90573.1411.03
Properties of materials used for the paste production.
Fig 1. XRD pattern of nano-SiO2, reprinted for educational purposes only 
The raw materials used are analysed clearly for making pastes of normal consistency and the water consistency is checked by Vicat method according to EN 196-3:1994.High strength cement (142.5) has been selected by the authors as the basis of testing. Nano grains are additionally tested so that composition and morphology can be identified and it is proven that nano particles are 100% amorphous material. The Transition Electron Microscopy clearly shows amorphous role of nano grains as the typical presence of...