Nano concrete

concrete which has enabled the study of chloride diffusion in concrete (which causes corrosion of reinforcement). Concrete is, after all, a macro-material strongly influenced by its nano-properties and understanding it at this new level is yielding new avenues for improvement of strength, durability and monitoring.

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1. Nano Concrete AGLAIA

2. INTRODUCTION The nanotechnology generated products have unique characteristics, and can significantly fix current construction problems, and may change the requirement and organisation of construction process. The recent developments in the study and manipulation of materials and processes at the nanoscale offer the great prospect of producing new macro materials, properties and products. But till date, nanotechnology applications and advances in the construction and building materials fields have been uneven. Exploitation of nanotechnology in concrete on a commercial scale remains limited with few results successfully converted into marketable products.

3. The main advances have been in the nanoscience of cementitious materials with an increase in the knowledge and understanding of basic phenomena in cement at the nanoscale . Concrete, the most ubiquitous material in the world, is a nanostructured , multi-phase, composite material that ages over time. It is composed of an amorphous phase, nanometer to micrometer size crystals, and bound water. The amorphous phase, calcium–silicate–hydrate (C–S–H) is the ‘‘glue” that holds concrete together and is itself a nanomaterial . Viewed from the bottom-up, concrete at the nanoscale is a composite of molecular assemblages, surfaces (aggregates, fibres ), and chemical bonds that interact through local chemical reactions, intermolecular forces, and intraphase diffusion. Properties characterizing this scale are molecular structure; surface functional groups; and bond length, strength (energy), and density.

4. The structure of the amorphous and crystalline phases and of the interphase boundaries originates from this scale. The properties and processes at the nanoscale define the interactions that occur between particles and phases at the microscale and the effects of working loads and the surrounding environment at the macroscale . Processes occurring at the nanoscale ultimately affect the engineering properties and performance of the bulk material. There are two main avenues of applications of nanotechnology in concrete research;the nanoscience and nano -engineering. Nanoscience deals with the measurement and characterization of the nano and microscale structure of cement-based materials to better understand how this structure affects macro scale properties and performance through the use of advanced characterization techniques and atomistic or molecular level modeling.

5. Nano -engineering encompasses the techniques of manipulation of the structure at the nanometer scale to develop a new generation of tailored, multifunctional, cementitious composites with superior mechanical performance and durability potentially having a range of novel properties such as: low electrical resistivity, self-sensing capabilities, self-cleaning, self-healing, high ductility, and self-control of cracks. Concrete can be nano -engineered by the incorporation of nanosized building blocks or objects (e.g., nanoparticles and nanotubes ) to control material behavior and add novel properties, or by the grafting of molecules onto cement particles, cement phases, aggregates, and additives (including nanosized additives) to provide surface functionality, which can be adjusted to promote specific interfacial interactions.

6. At the basic science level, much analysis of concrete is being done at the nano -level in order to understand its structure using the various techniques developed for study at that scale such as Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Focused Ion Beam (FIB). This has come about as a side benefit of the development of these instruments to study the nanoscale in general, but the understanding of the structure and behaviour of concrete at the fundamental level is an important and very appropriate use of nanotechnology. One of the fundamental aspects of nanotechnology is its interdisciplinary nature and there has already been cross over research between the mechanical modeling of bones for medical engineering to that of concrete which has enabled the study of chloride diffusion in concrete. Concrete is, after all, a macro-material strongly influenced by its nano -properties and understanding it at this new level is yielding new avenues for improvement of strength, durability and monitoring.

7. Addition of nanosized and nano -structured materials Nanosized particles have a high surface area to volume ratio, providing the potential for tremendous chemical reactivity. Much of the work to date with nanoparticles has been with nano -silica (nano-SiO2) and nano -titanium oxide (nano-TiO2) . There are a few studies on incorporating nano -iron (nano-Fe2O3), nano -alumina (nano-Al2O3) , and nanoclay particles . Additionally, a limited number of investigations are dealing with the manufacture of nanosized cement particles and the development of nanobinders . Nanoparticles can act as nuclei for cement phases, further promoting cement hydration due to their high reactivity, as nanoreinforcement , and as filler, densifying the microstructure and the ITZ, thereby, leading to a reduced porosity.

8. The most significant issue for all nanoparticles is that of effective dispersion. Though it is particularly significant at high loadings, even low loadings experience problems with self-aggregation, which reduces the benefits of their small size and creates un-reacted pockets leading to a potential for concentration of stresses in the material.

9. Nano-SiO2 has been found to improve concrete workability and strength, to increase resistance to water penetration, and to help control the leaching of calcium, which is closely associated with various types of concrete degradation. Nano-SiO2, additionally, was shown to accelerate the hydration reactions of both C3S and an ash–cement mortar as a result of the large and highly reactive surface of the nano particles. Nano-SiO2 was found to be more efficient in enhancing strength than silica fume. Addition of 10% nano-SiO2 with dispersing agents was observed to increase the compressive strength of cement mortars at 28 days by as much as 26%, compared to only a 10% increase with the addition of 15% silica fume. Even the addition of small amounts (0.25%) of nano-SiO2 was observed to increase the strength, improving the 28 day compressive strength by 10% and flexural strength by 25%.

10. It was noted that the results obtained depended on the production route and conditions of synthesis of the nano-SiO2 (e.g., molar ratios of the reagents, type of reaction media, and duration of the reaction for the sol–gel method) and that dispersion of the nano-SiO2 in the paste plays an important role. Nano-SiO2 not only behaved as a filler to improve the microstructure but also as an activator to promote pozzolanic reactions .

11. Nano-TiO2 has proven very effective for the self-cleaning of concrete and provides the additional benefit of helping to clean the environment. Nano-TiO2 containing concrete acts by triggering a photocatalytic degradation of pollutants, such as NOx , carbon monoxide, VOCs, chlorophenols , and aldehydes from vehicle and industrial emissions. ‘‘Self-cleaning” and ‘‘de-polluting” concrete products are already being produced by several companies for use in the facades of buildings (e.g., the Jubilee Church in Rome, Italy). In addition to imparting self-cleaning properties, a few studies have shown that nano-TiO2 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

12. APPLICATION OF NANOTECHNOLOGY IN CONSTRUCTION Application in concrete: Addition of nano scale materials into cement could improve its performance. Use of nano-SiO2 could significantly increase the compressive for concrete, containing large volume fly ash, at early age and improve pore size distribution by filling the pores between large fly ash and cement particles at nano scale. The dispersion/slurry of amorphous nano silica is used to improve segregation resistance for self-compacting concrete. It has also been reported that adding small amount of carbon nanotube (1%) by weight could increase both compressive and flexural strength.

13. Application in Steel The new steel was developed with higher corrosion-resistance and weld ability by incorporating copper nano particles from at the steel grain boundaries. Coating The coatings incorporating certain nano particles or nano layers have been developed for certain purpose. It is one of the major applications of nanotechnology in construction.

14. Nanosensors They have been developed and used in construction to monitor and/or control the environment condition and the materials/structure performance. One advantage of these sensors is their dimension (10  -9 m to 10 -5 m). These sensors could be embedded into the structure during the construction process. The sensors can be used to monitor concrete corrosion and cracking. The smart aggregate can also be used for structure health monitoring. The disclosed system can monitor internal stresses, cracks and other physical forces in the structures during the structures’ life. It is capable of providing an early indication of the health of the structure before a failure of the structure can occur.

15. CONCLUSION Nanotechnology offers the possibility of great advances whereas conventional approaches, at best, offer only incremental improvements in the field of construction engineering. It is not exactly a new technology, rather it is an extrapolation of current ones to a new scale and at that scale the conventional tools and rules no longer apply. It is the opposite of the traditional top-down process of construction, or indeed any production technique, and it offers the ability to work from the “bottom” of materials design to the “top” of the built environment. many of the advances offered by nanotechnology, be they for economic or technical reasons, are years away from practical application, especially in the conservative and fragmented construction business.

16. The main limitation is the high costs of nanotechnology, also concerns with the environmental and health effects. The waves of change being propagated by progress at the nano scale will therefore be felt far and wide and nowhere more so than in construction due its large economic and social presence. There are three main issues that are preventing the widespread use of the nanotechnology (1) Lack of vision to identify those aspects that could be changed through its use. (2) Lack of skilled personnel (3) Level of investment.

17. The potential of nanotechnology to improve the performance of concrete and to lead to the development of novel, sustainable, advanced cement based composites with unique mechanical, thermal, and electrical properties is promising and many new opportunities are expected to arise in the coming years. However, current challenges need to be solved before the full potential of nanotechnology can be realized in concrete applications, including proper dispersion; compatibility of the nanomaterials in cement; processing, manufacturing, safety, and handling issues; scale-up; and cost.

18. REFERENCES Tina Lai "Structural behavior of Nano Concrete and their applications to lightweight bridge decks" , M.Tech thesis, MIT, 2009. Sergiu Cal in, Ciprian Asavoaie and N. Florea , "Issues for achieving an experimental model" Bul. Inst. Polit. lai , t. LV (LIX), f. 3, 2009. Martina Schnellenbach -Held and Karsten Pfeffer,"Punching behavior of biaxial hollow slabs" Cement and Concrete Composites, Volume 24, Issue 6, Pages 551-556, December 2002. Sergiu Calin , Roxana Glntu and Gabriela Dascalu , "Summary of tests and studies done abroad on the Nano Concrete system", The Buletinul Institutului Politehnic din la, t. LV (LIX), f. 3, 2009.

19. T h a n k y o u For more…. [email protected]