CEE April-June 2012

silicate chain length. CSH molecules enhanced with polymers are more resistant in crack forming [5). Enhancement of the C-S-H Nanomolecular structure by using CNT( Carbon Nano Tube) and CNF (Carbon Nano Fibre) Carbon nanotubes and carbon nanofibers (CNTs /CNFs) exhibiting extraordinary strength with moduli of elasticity on the order of TPa and tensile strength in the range of GPa, are potential candidates for use as nano reinforcements in cement-based materials. Also CNTs and CNFs have self-sensing properties and can provide unique properties preventing crack forming and propagation. SWCNTs (single-wall) and MWCNTs (multi-wall) provide crack bridging when time of forming cracks and fractures in concrete. As using reinforcements CNTs and CNFs in concrete, new properties transferred from nanoscobic level to macroscobic level. Beside the enhancement effect of CNT, due to its filler effect forming more dense structures so increases the quality of paste– aggregate interface at early ages [5) . The development of high-performance cementitious nanocomposites reinforced with multiwall carbon nanotubes was studied by Maria S. Konsta et al [34]. It was found that small amounts of effectively dispersed MWCNTs (0.025- 0.08 wt. per cent of cement) can significantly increase the strength and the stiffness of the cementitious matrix. In particular, lower amounts of MWCNTs (0.025 - 0.048 wt.%) provide effective reinforcement. It was also found that effectively dispersed MWCNTs provide a unique role in cement based materials. The nanoindentation results suggest that MWCNTs can strongly modify reinforce the nanostructure of the cementitious matrix. Compared to plain cement matrix, the nanocomposites appear to have a higher amount of high stiffness C-S-H and reduced nanoporosity. Due to their small diameters (20 - 40 nm) MWCNTs appear to specifically reduce the amount of fine pores. This phenomenon leads to the reduction of the capillary stresses, resulting in beneficial effect on the early strain capacity of the nanocomposites [34]. CNTs supply economical contributions decreasing the amount of cement using in concrete production. CNTs supply positive contributions to the environment by decreasing the amount of sera gases emissions. They decreases the consumption of natural resources. They increase the service life of concrete. Meanwhile the main reason for their limited usage is due to their high production costs. On the other hand when considering cost– performance relation , it is thought that in the case of using in critical fields like bridges, nuclear reactor channels, the dams constructed at high risk areas, oil wells and military bases these costs can be recovered [3, 5, 12, 15]. It is certain that nanotechnology will do an effect on the nature of construction Figure 5. ACNT Example of crack bridging in a SWCNT/hydrated OPC composite bridging structures are SWCNT bundles [5]. Nanotechnology in terms of environment, health and economy in cement and concrete industry Although the advantages of using nanotechnological methods and nano additives were emphasized so far, the risk of inhaling the nano sized particles should be seriously considered when such materials are handled. Possible toxic effects of nanotechnolgical products are related with their specific surface area and their activity instead of their amounts. Their possible deleterious effects on the flora and fauna when they are released to the environment should be considered, also. Current specifications and regulations may not be sufficient for nanotechnological products and processes. So, while increasing nanotechnology usage and gaining the new advances it is obligatory to carry out new arrangements relating health and environment at the same time [2, 29). References 1. Ankara Oniversitesi Rasathanesi - Bayuk Bayutlar BOyOk Saylar 2. Erik Bakker, "Nanotechnology and human health in the construction industry': the short internship in industry performed at IVAM BV Amsterdam as part of the larger curriculum for the degree of MSc, NanoScience, 2008 3. Florence Sanchez, Konstantin Sobolev, "Nanotechnology in concrete - A review", Construction and Building Materials" 24 (2010) 2060 - 2071 4. Samule C. Halim, for the degree of Doctor of Sciences Prof. Dr. WJ. Stark, examiner Prof. Dr. E. J. Windhab, co.-examiner ZOrich 2008 5. Raki, L; Beaudoin, J. J.; Alizadeh, R; Makar, J.M. ; Sato, T. "Cement and concrete nanoscience and nanotechnology~ 2010 17