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Nano Technology in Construction

Dr. Manamohan R Kalgal

Head, Technical Services, UltraTech Cement Ltd.

The word nano, is derived from the Greek "nanos" (or Latin "nanus"), meaning "Dwarf". Nano refers to the 10-9 power, or one billionth. Generally one refers to a nanometer, which is on the scale of atomic diameters. To get an idea of what size is being talked about in layman terms, a human hair is about 100,000 nanometers thick! Nano-science is the study of atoms, molecules, and objects whose size is on the nanometer scale (1 - 100 nanometers).Physics is different on the nanometer scale. Properties not seen on a macroscopic scale now become important- such as quantum mechanical and thermodynamic properties. Rather than working with

bulk materials, one works with individual atoms and molecules. By learning about an individual molecule's properties, one can put them together in very well-defined ways to produce new materials with new and amazing characteristics.

Nanotechnology is the re-engineering of materials and devices by controlling the matter at the atomic level.Nanotechnology is not a new science or technology; rather it was first introduced by Richard P. Feynman in his famous lecture at the California Institute of Technology in 1959.However, the research on this topic has been very active only in recent two decades.Today, Nanotechnology is one of the most active research areas that encompass a number of disciplines including civil engineering and construction materials. Traditionally, nanotechnology has been concerned with developments in the fields of microelectronics, medicine and materials sciences. However, the potential for application of many of the developments in the nanotechnology field in the area of construction engineering is

growing.

Behavior at Nano Level

The size of the particles is the critical factor. At the nanoscale (anything from one hundred ormore down to a few nanometres, or 10^-9m) material properties are altered from that of largerscales (the exact point at which this occurs depends on the material). It is as if there is an invisible threshold or boundary for each material, as we go down in scale. There is a dramatic change in situation at that boundary. On one side, above the boundary, the world is pretty much as we experience it every day, the laws, effects and consequences that are apparent and important to us at our size are still important and determine the nature of things. On the other side things are quite different and we cannot simply reduce the size of our tools or machines to cope. Different things start to happen below the boundary e.g. gravity becomes unimportant, electrostatic forces take over and quantum effects kick in. Another important aspect is that, as particles become nano-sized, the proportion of atoms on the surface increases relative to those inside and this leads to novel properties. It is these "nano-effects", however, that ultimately determine all the properties that we are familiar with at our "macro-scale" and this is wherethe power of nanotechnology comes in - if we can manipulate elements at the nanoscale we can affect the macro-properties and produce significantly new materials and processes.

Its potential for development is such that itis often considered as the industrial revolution of the 21^st century. Applications ofNanotechnology are expected to lead to better, cleaner, cheaper, faster and smarterproducts. In addition, much more effective use of basic resources and development ofenvironmentally sustainable productionprocesses is predicted. 

Nanotechnology in Construction

According to a new study by the Canadian Program on Genomics and Global Health (CPGGH) at the University of Toronto Joint Centre for Bioethics (JCB), a leading international medical ethics think-tank, several nanotechnology applications will help people in developing countries tackle their most urgent problems.According to this study, the top 10 nanotechnology applications are: (1) Energy storage, production and conversion; (2) Agricultural productivity enhancement; (3) Water treatment and remediation; (4) Disease diagnosis and screening; (5) Drug delivery systems; (6) Food processing and storage; (7) Air pollution and remediation; (8)Construction; (9) Health monitoring; (10) Vector, pest detection and control. Thus Nanotechnology in Construction is one of the top ten answers to world's biggest problems. 

Nano-materials offer many improved performance properties for concrete, coatings, adhesives, flooring, glass, lighting equipment, plumbing fixtures and other construction products. Nano-materials are poised for wide spread use in the construction industry, where they can offer significant advantages for a variety of applications ranging from making more durable concrete to self-cleaning windows. The extraordinary chemical andphysical properties of materials at the nanometer scale enable novel applications ranging from structural strength enhancement and energy conservation to anti-microbial properties and self-cleaning surfaces. Various Nano-materials and Nano-composites are being considered for various uses in the construction and related infrastructure industries.

The main Nano-materials which could be used in Construction materials are:

Nano Silica (SiO₂), Titanium Dioxide (TiO₂), Carbon Nanotubes (CNT) 

Nanotechnology in Cement and Concrete

The binding process of cement is based on the slow re-crystallization and precipitation of calcium silicate species. Since the material's reactivity is dependent on surface area, a reduction in particle size of Portland cements has been used to prepare faster binding formulations. A recent work has investigated a new and direct, one-step preparation of calcium silicate-based nanoparticles of a typical Portland cement composition by flame spray synthesis. Isothermal calorimetry revealed that the hardening of this new nano-cement corroborated a more than tenfold increase of initial reactivity with different reaction kinetics if compared to conventionally prepared cements. At present, the unfavorably high porosity of nano-cements, however, underlines the need for additional improvements of chemical composition and formulation to make these highly reactive materials applicable to modern construction work.

Research has shown that controlling the composition and particle size of nano-additives for cement can help produce materials with advantageous properties.

 Silicon dioxide and iron oxide nanoparticles have been shown to have an advantageous effect on the compressive strength and flexural strength of cements, and also accelerate the hydration process. Making cement as strong as possible will reduce the amount needed in building, leading to a more efficient construction. Cement making is a highly energy-intensive process, so making the most of the cement which is produced is very important in sustainable construction. 

As reported, much analysis of concrete is being doneat the nanolevel in order to understand its structure usingthe various techniques developed for study at that scale using Atomic Force Microscopy (AFM), ScanningElectron Microscopy (SEM) and Focused Ion Beam (FIB).The understanding of the structure and behavior of concreteat the fundamental level is an important and veryappropriate use of nanotechnology.

Nano Silica mixed in Concrete can improve:

• Mechanical Properties due to densification of the micro and nanostructure
• Can Control the degradation of the fundamentalC-S-H(Calcium-Silicate-Hydrate)reaction of concrete.
• Related to improved particle packing, high energy milling of ordinary portland cement (OPC) clinker and standard sand, produces a greater particle size diminution with respect to conventional OPC and, as a result, the compressive strength of the refined material is also 3 to 6 times higher (at different ages).
• Can block water penetration and therefore lead to improvements indurability.
• They also increase strength as well as offering the benefit of monitoring stress levels through the measurement of section electrical resistance. 

Carbon Nanotube (CNT)is used to strengthen and monitor concrete.The addition of small amounts(1%wt)of CNTs can improve the mechanical properties of samples.Oxidized multi-walled nano tubes(MWNTs)show the best improvements both in compressive strength(+25N/mm2) and flexural strength(+8N/mm2) However,two problems with the addition of carbon nanotubes to anymaterial are the clumping together of the tubes and the lackof cohesion between them and the matrix bulk material.Additional work is needed in order to establish the optimumvalues of carbon nanotubes and dispersing agents in the mixdesign parameters. In addition, the cost of adding CNT’s toconcrete may be prohibitive at the moment. Nanotechnology in Steel Fatigue failure commonly occurs when steel is subjected

to cyclic loading,such as in bridges or in towers. This can happen at stressessignificantly lower than the yield stress of the material andlead to a significant shortening of useful life of the structure. Stress risers are responsible for initiating cracksfrom which fatigue failure results and research has shownthat the addition of copper nanoparticles reduces the surfaceunevenness of steel which then limits the number of stressrisers and hence fatigue cracking.

When the tensile strength of tempered martensite steelexceeds 1,200 MPa, even a very small amount ofhydrogen embrittles the grain boundaries and the steelmaterial may fail during use. This phenomenon, which isknown as delayed fracture, has hindered the furtherstrengthening of steel bolts and their highest strength islimited to somewhere around 1,000 to 1,200 MPa.Research work on vanadium and molybdenum nano particles has shown that they improve the delayedfracture problems associated with high strength bolts. 

FHWA together with American Iron and SteelInstitute and the U.S. Navy started to develop new, low carbon, high-performance steel(HPS) for bridgesin 1992. The new steel was developed with higher corrosion-resistance and weld abilityby incorporating copper nanoparticles from at the steel grain boundaries. 

SandvikNanoflexTM is new stainless steel with ultra-high strength, good formability, and a good surfacefinish developed by SandvikNanoflex Materials Technology. Due to its high performance, SandvikNanoflexTM is suitable for application where requires lightweight and rigid designs. For certainapplications, the components could be even thinner and lighter than that made from aluminium andtitanium due to its ultra-high strength and modulus of elasticity. Its good corrosion and wear resistance can keep life-cycle costs low. Attractive or wear resistant surfaces can be achieved by various treatments(SandvikNanoflex Materials Technology).

MMFX2 is nanostructure-modified steel, produced by MMFX Steel Corp. Compared with theconventional steel, it has a fundamentally different microstructure- a laminated lath structure resemblin "plywood". This unique structure provides MMFX2 steel with amazing strength (three times stronger),ductility, toughness, and corrosion resistance. Due to the high cost, the stainless steel reinforcement inconcrete structure is limited in high risk environments. The MMFX2 steel could be an alternative becauseit has the similar corrosion resistance to that of stainless steel, but at a much lower cost (MMFX SteelCorp.).

Nanotechnology in Surfaces and coatings

A number of companies are using nanotechnology to add special characteristics to product surfaces, which can be anything from stain-resistance and colour durability to self-cleaning, improved hardness and scratch-resistance, corrosion and UV resistance, and improved thermal performance.

Titanium Dioxide(TiO₂) Nano-powder is incorporated to block UV light and it is added to paints, cements and window glass for its sterilizing properties since TiO₂ breaks down organic pollutants, volatile organic compounds and bacterial membranes through powerful catalytic reactions. TiO₂ is a white pigment and can be used as an excellent reflective coating. Additionally, itis hydrophilic and therefore gives self-cleaning properties tothe applied surfaces. In this process rain water is attractedto the surface and forms sheets which collect the pollutantsand dirt particles previously broken down and washes themoff. The resulting concrete has a white colour that retains itswhiteness very effectively. 

Nanotechnology also has the potential to bring antimicrobial properties to surfaces. In 2007, research from Yale University found that carbon nanotubes were effective at killing E. coli bacteria. 

Insulating Nanomaterials 

Nano materials designed for use as insulation in buildings are already commercially available. The unique properties of nanomaterials can offer enhanced performance coupled with additional useful properties not available from conventional materials.  Aerogels are nanoporous solids which are incredibly lightweight - around 95% of their volume is taken up by air. This makes them very good insulating materials (2-3 times more effective than conventional insulation materials), but also means they can be translucent. Aerogel is an especially light weight material that can for example be produced from silica. The gel is dried in a special process, yielding a type of solid foam that consists of more than 95% air. Such silica aerogels were first

produced back in the 1930s. The pores of this material measure only a few nanometers, explaining the brand name Nanogel®. The thermal conductivity of a material with pores on the nano-scale is minimal because only a few gas molecules have space in the pores, thus reducing the heat transfer from one gas particle to another. Aerogel holds 15 entries in the Guinness Book of records, among others as the "best insulator" and "lightest solid". Combining Aerogel and stone wool yields so-called Aerowolle®, which is incorporated into thin plasterboard for interior insulation. Aerogel can also be filled in between two window glass panes. Such glazing successfully blocks infrared radiation as well as noise. Nonetheless, Aerogel is not transparent, yielding a "translucent glass" effect. An insulating plaster with Aerogel is currently under development and is expected to be on the market in 2013. 

Nanotechnology for Wood Recent nanotechnology research in forest products, focusing on the nanoscale properties of wood, hopes to develop advanced nanomaterials. Wood densification, chemical modification, or impregnation by resins could improve hardness, wear and decay resistance. Nanotechnology offers the potential to transform the forest products industry in virtually all aspects, including production processes (raw materials,  engineered wood and wood-based materials), improved neergy efficiencies, new applications for composite and paper products and composites made from nanocrystals.

Nanotechnology in Ground stabilization in road construction

In order to protect a road from frost damage, the roadbed must be properly prepared. Novel polymer dispersions with nanoscale silicon dioxide, which is mixed into the cement, are designed to extend the durability of roads while at the same time promising improved workability. Like in ultra high performance concrete, the SiO₂-nanoparticles fill out the interspaces of the concrete particles, yielding a particularly uniform and dense concrete matrix. Moreover, the polymers in the dispersion are also water repellent. This decreases the water absorption capacity of the road foundation and improves frost resistance. These novel additives promise additional advantages: locally available materials (sand, clay or excavated earth) can be used to produce the roadbed, whereby less material needs to be transported. The setting process of binding agents (for example cement) and the polymer additive can take place using either freshwater and saltwater, and processing is possible even at temperatures below -10° C. According to the manufacturer, these nanopolymer dispersions are also suitable for sealing- and baselayers in hydraulic engineering projects and sewer canal construction, as well as in dam and landfill site construction. 

Fire protection

Special fire-resistant glass consists of two glass panes with an only 3-mm-thin filling of nanoscale SiO₂, which foams in the event of a fire. Such panes can withstand a continuous fire of more than 1000 °C for up to 120 minutes; they have the additional advantage of being very light and thin. The coating itself is hardly visible. Beyond applications in buildings, these panes are also used for ship windows and portholes. Using nano-SiO₂, lightweight sandwich panels of straw and hemp, such as those used in trade fair construction, can be coated and made fire resistant. Despite the glass-like coating, the panels are diffusible and, at the end of their useful life, can be normally shredded and disposed of. Nano-structured silicate particles ("nano-clay") can be incorporated in plastics to optimize their flame-retardant properties and their heat resistance. Such nanocomposite materials are for example applied in producing cable insulation or covers (e.g. fuse boxes, sockets) in interior finishings. 

Nanotechnology for sensing

The ability of nanotechnology to constantly monitor materials could offer better predictionof service life and life cycle performance of thebridges. During construction, nanotechnology could allow for embedding increasingly small sensors throughout a structure or pavement. These sensors could be used for long-term monitoring of corrosion and could offer an invaluable toolin monitoring deterioration and cracking in concrete without physical intervention. Similarly,these sensors could monitor vibrations and loadson bridges and enable researchers to assess weaknesses and fix them long before they are apparent to human inspectors. It has also beenassessed that the road sensor networks could gather and provide data to transportation operators to manage congestion and accidents on roads in abetter way.

Concluding Remarks

Nanotechnology is set to become as pervasive as other previous material revolutions. For the present, the issues of cost and relatively small number of practical applications have masked what revolutions it can bring. There is a need to understand the hazards that the nanoparticles may bring in terms of possible inhalation, ingestion and difficulty in safe disposal. But efforts are on to look as the benefits holistically and overcome the problems which are not surmountable.  The sheer size and scope of nanomaterials in construction industry promise huge technological and economic impact.

References:

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2. Peter J. M. Bartos, Nanotechnology in Construction: A Roadmap for Development, Proceedings of ACI Session on “Nanotechnology of Concrete: Recent Developments and Future Perspectives”, November 7, 2006, Denver, USA
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4. Halim S C et alPreparation of an ultra fast binding cement from calcium silicate-based mixed oxide nanoparticles, Nanotechnology,Volume 18, No. 39, 2007

5.AmitSrivastava and Kirti Singh, Nanotechnology in Civil Engineering and Construction: A Review on State of The Art and Future Prospects, Proceedings of Indian Geotechnical Conference December 15-17, 2011

1. Will Soutter,  Nanotechnology in Green Construction, (http://www.azonano.com/article.aspx?ArticleID=3093)