CEE April-June 2012

In addition to this, due to large surface area of nano silica water needs is increased is to keep the workability and internal friction appears between solid particles but using super plasticizers this disadvantage is removed. There is an increase in setting rate, however the time difference is decreased between initial and ending setting times. Mechanical properties are investigated; using nano silica at the rate of 3 - 10 per cent, only initial compressive strengths is increased by provided well– arranged dispersion, on the other hand in the case of using Figure 3. An example of self-cleaning concrete pavement (The jubilee Church in Rome one of the most often quoted successes of photo catalytic concrete by the addition of Ti02. Material: TX Active (TXArea) from the ltalcementi group.)[33]. nano silica in much more amounts, it is observed a decrease in the compressive strength instead increasing effect. Because there are forming dryings and cracks due to much more water needs. Besides, more important thing from pore filling effect of nano silica is that it increases the pozzolanic reactivity significantly. On the other hand, in another investigation, nano alumina and nano iron oxide were used together with nano silica and the mixture was found to increase the compressive strength when used upto 1.5 per cent (by weight of cement). Beyond that level , it reduced the 28-day strength [32]. The best results for compressive strength and capillary permeability at the end of day 180 were obtained with 1.25 per cent nano AI 203 powder in single uses, 0.5 per cent nano-Si02 + nano AI20 3 powder in binary combinations. and 0.5 per cent in ternary combination. The finding of the experiments suggested the conclusion that the improvement in the mechanical and physical properties of mortars was caused by the rise in pozzolanic activity of the nano powders rather than the filler effect [32]. Considering the above-mentioned experimental results, it can be stated that nano sized particles do not contribute to long term strengths, significantly. The most probable reason for this would be the flocculation of these very fine particles and thus loosing their reactivity during the hydration process. Silica fume has nano dimensions naturally and including almost all main basic cement oxides in own composition, using as additive provides improvements at least as much as valuable nano Si0 2, Al 20 3, and Fe20 3 in cement and concrete. Nano-TI02 containing concrete acts by triggeringa photo catalytic degradation of pollutants, such as NO•. carbon monoxide , chlorophenols, and aldehydes from vehicle and industrial emissions. In addition to imparting self-cleaning properties, a few studies have shown that nano-no2 can accelerate the early age hydration of Portland cement, improve compressive and flexural strengths, and enhance the abrasion resistance of concrete. However, it was also found that aging due to carbonation may result in loss in catalytic efficiency [3]. Nano-Fe 20 3 has been found to provide concrete with self-sensing capabilities due to piezo resistive properties as well as to improve its compressive and flexural strengths [3]. Some materials like quartz being the best known. when compressed by a force or a load, electric charges are collected to different sides due to crystal structure of the matter and this causes a kind of electric potential, such as magnetic lighter, car airbags and the sonar etc. instruments work according to this rule. There is also validity for the opposite of this rule, that is if an electric potential is applied to a piezo resistive material , this results in a compression on material, in other words a change is wieved on the material dimensions. Figure 4a. Smart concrete structures (shor conducting fibre 15