the impact of nanoscale technologies in Glazed building envelopes

NANOTECHNOLOGIESAND SMART MATERIALSFOR SHM

edited by

Agostino CatalanoGiovanni FabbrocinoCarlo Rainieri

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The present volume has been published in the frameworkof the activities of the Italy-USA Executive Programmepromoted by the Ministry of Foreign Affairs, DirectorateGeneral for the Promotion of the “Country System”, whosesupport is gratefully acknowledged.

Referee

This volume has undergone a preventive evaluation bytwo external referees from Italian Universities of thefollowing scientific sectors:

Prof. Eng. Maria Antonietta Aiello(SSD ICAR/09 – Tecnica delle costruzioni)of the Università degli Studi del Salento

Prof. Eng. Romualdo Montagna(SSD ICAR/10 – Architettura tecnica)of the Università Politecnica delle Marche

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edited by


Structural and

Geotechnical dynamicS

laboratory StreGa EDITRICE

NANOTECHNOLOGIESAND SMART MATERIALS FOR SHM

edited by


Under the support of

University of MoliseStructural and Geotechnical Dynamics Laboratory StreGa

Ministry of Foreign AffairsDirectorate General for the Promotion of the Country System

Printed on April 2012Arti Grafiche La Regione EditriceISBN: 978-88-88102-47-4

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NANOTECHNOLOGIES AND SMART MATERIALS FOR SHM

the impact of nanoscale technologies in Glazedbuilding envelopes

m. cristiano1

1Ph.D., University of Molise, Via Duca degli Abruzzi – 86039Termoli, Italy

abstract

The development of research on the structure of matter and its properties, ona nano-metric scale has led to two distinct branches of study.The first aims at the understanding of the origin of the exceptional propertiesof materials and products, expressed on the metric scale, which derive theseproperties from nano-metric components, naturally or accidentally occurring.The second investigates instead the methods of production on a nano-metricscale, to enrich with new and exceptional properties traditional materials andproducts.A prime example cited in the illustration of the history of nanotechnology isglass whose peculiar colors is derived from microscopic inclusions obtainedwith traditional technologies.Even today the combination of nanotechnology and glass is examined toprovide the material, a symbol of modern international architecture, withfeatures to guarantee performance levels necessary to ensure the best qualityof life and reduce energy consumption in buildings.This article presents the wide range of nano-scale technologies that increasethe efficiency and fields of use of glass elements in architecture.

introduction

Nanotechnology, the manipulation of matter at the molecular scale, is bringingnew materials and new possibilities to industries as diverse as electronics,medicine, energy and aeronautics. New materials and products based on nanotechnology can be found in buildinginsulation, coatings, and solar technologies and has already brought to themarket self-cleaning windows, smog-eating concrete, and many otheradvances.For example a patented nanocomposite insulate made with Hydro-NM-Oxide,a liquid applied coating, dries to a thin layer and provides exception insulation,

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corrosion protection, prevents mold and rust, and has proven to provide energysavings in a variety of insulation applications since it has a very low measuredthermal conductivity value.Another product of nanotechnology introduced to the building industry isaerogel, the lightest weight solid in the world. The gel is filled with gas ratherthan liquid and is 95% air and 5% solid. Yet, it can support over 2000 times itsown weight. A 3.5 inch thick aerogel panel provides an R-value of R-28 and areavailable with up to 75 percent translucency.It doubles the insulation and light transmission values of skylights and otherdaylighting technologies, enabling architects to design buildings with morenatural light, reducing energy consumption.Aerogel is currently being used for its unique characteristics likehydrophobicity and ultra-low thermal conductivity in products ranging fromarchitectural day lighting systems to oil and gas pipeline insulation.This technology was applied for the transparent building envelope at the YaleUniversity Sculpture Building Need: Maintain (2007) [fig. 1] a predominantlyglazed envelope, without compromising the building’s high level of energyperformance.

Fig. 1. yale university Sculpture building - external view

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To maintain a predominantly glazed envelope, without compromising thebuilding’s high level of energy performance, the project installed a triple-glazed curtain wall of insulated glass and super insulated R-20aerogel-insulated translucent panels. This high performance curtain wall provides significant reductions in both heatgain and loss year round. The building’s transparent, lightweight façade system transmits soft, glowinglight through 8ft operable windows, triple-glazed low-E vision panels, and atranslucent double-cavity spandrel panel using aerogel [fig. 2].

Fig. 2. yale university Sculpture building - internal view

Now that building architecture is often transparent, and that for eachcomponent in the envelope a high energy performance is essential, glazedelement must meet many requirements.This malleable material, has undergone continuous evolution in the course ofits history, its physical properties have increased with the improvement ofproduction techniques, and found materials with other unions and othertechnologies to better meet the requirements expected.

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As for the building envelope, the functions which the glazing elements mustguarantee can be divided into three classes:

1) - Protection from external actions: weather (eg rain, wind), heat loss,solar radiation, intrusion.2) - Comfort for users: lighting, ventilation, insulation, visual.

These two then add the aesthetic considerations that are not mere artisticambitions, but a real need and expectation:3)-Beauty, recognition and identification, to which the engineer is obligedto respond.

benefits in glazed surfaces

Nanoparticles are invisible due to the fact that they are smaller than thewavelength of visible light and therefore unable to scatter light. For thisreason, a solution that contains a 60% proportion of solids in the form ofnanoparticles can still be transparent.Therefore glazed surfaces can be enriched with extraordinary propertieswithout compromising their fundamental characteristics.To control, harvest and redirect energy at various wavelengths nanometricscale additives or films are applied to glass to guarantee: UV/IR filtering and reflecting properties for control of unwanted solar heat; Self-Cleaning Glass with hydrophilic and grime removing layers; Anti-reflective glazing for high visibility; Thin-film insulation to enhance the R value of the transparent surfaces;Property mutating systems such as photocromic, termochromic, andelettrochromic windows.Describing briefly these technologies, all commercially available today, we willanalyze in particular the chromogenic windows that can change their color,and therefore their optical properties, when subject to specific stimuli. It is certainly relevant that these technologies are all aimed at reducing theshortcomings of glazed building components and that the vast majority ofthese faults are tied to energy management.In the list of examples mentioned, which is by no means complete, only the“self-cleaning” coatings are tied to the containing the maintenance cost. These elements in addition to a hydrophilic property, also utilize photocatalysisto decompose organic contaminants. The usual basis of these coatings istitanium dioxide (TiO2) applied pyrolytically.The photocatalytic action is activated by ultraviolet radiation and it breaks downorganic deposits in contact with the coating, causing them to lose adhesion,and making them more likely to be rinsed off of the hydrophilic surface by rain,or more easily removed by washing.

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The other example that does not concern energy management is anti-reflective coatings. Anti-reflective coatings function by progressing from low to high indices ofrefraction through one or more coating layers. Pyrolytic and cold-appliedsputtered stacks and baked-on dip coatings are commercially available. Visibletransmittance of these products ranges from approximately 1% to less than0.5%. Low-iron glass, with antireflective coatings, is virtually invisible frommost angles under many lighting conditions.Use of anti-reflective glazing is widespread in display cases, storefronts,sports venues, and other vision-critical applications.But reducing heat loss and heat gain through windows is critical to reducingenergy consumption in buildings, and achieving the zero emission buildingswe have committed to.Nanotechnology is reducing heat loss and heat gain through glazing thanks tothin-film coatings, thermochromic, photochromic and electrochromictechnologies. Thin film coatings are spectrally sensitive surface applications for windowglass that filter out unwanted infrared light to reduce heat gain in buildings.Infrared (IR) rays can also be blocked using transparent IR-absorbing coatingsfor heat-absorbing films for windows.Low emission glazing (Low-E), first introduced in 1979, has a low rate ofemission – that is it has a lower rate than clear float glass of allowing heat topass through the glass.Two different production methods exist to apply these nanometric scale films:online coated Low-E (hard coat) and offline coated Low -E (soft coat). The first is accomplished by pouring a thin layer of metallic oxide onto a sheetof glass while the glass is still on the float line, just after it has been formedinto a thickness ribbon. The metallic oxide layer actually becomes “welded”to the glass surface. This process makes it very difficult or “hard” to scratchor remove the coating, usualy giving it a bluish tint.The second, called sputtering, involves the application of silver, zinc or tin (ora combination of) to glass that has already been formed and taken off the floatline. The glass enters a vacuum chamber filled with an inert gas which iselectrically charged. The electricity combined with the vacuum allowsmolecules of metal to sputter onto the glass. This second method, suitable for the creation of multiple layered films, is usedfor the production of the chromogenic finish of glass.Thermochromic technologies are being studied which react to changes intemperature and provide thermal insulation to give protection from heatingwhile maintaining adequate lighting. Photochromic technologies react tochanges in light intensity by increasing their light absorption. Electrochromic devices change light transmission properties, using usually atungsten oxide layer, in response to voltage and thus allow control over the

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amount of light and heat passing through and reducing undesirable effectssuch as fading, glare. In electrochromic windows, the electrochromic materialchanges its opacity: at any stage between a colored, translucent state (usuallyblue) [fig. 3] and a transparent state [fig. 4]. The action of an electric fieldsignals the change in the window’s optical and thermal properties.

Fig. 3 electrochromic windows - tinted state

Fig. 4 electrochromic windows - clear state

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Once the field is reversed, the process is also reversed. The windows operateon a very low voltage — one to three volts — and only use energy to changetheir condition, not to maintain any particular shade which has been reached.Electrochromic glass provides visibility even in the darkened state and thuspreserves visible contact with the outside environment. Recent advances inelectrochromic materials pertaining to transition-metal hydride electrochromicshave led to the development of reflective hydrides, which become reflectiverather than absorbing, Thin films made of nickel-magnesium alloy are able toswitch back and forth from a transparent to a mirror-like reflective state.To make an electrochromic window, a thin, multi-layer assembly issandwiched between traditional pieces of glass. The two outside layers of theassembly are transparent electronic conductors. Next is a counter-electrodelayer and an electrochromic layer, with an ion conductor layer in-between.When a low voltage is applied across the conductors, moving ions from thecounter-electrode to the electrochromic layer cause the assembly to changecolor. Reversing the voltage moves ions from the electrochromic layer backto the counter-electrode layer, restoring the device to its previous clear state.The glass may be programmed to absorb only part of the light spectrum, suchas solar infrared.

conclusions

The technologies, exemplify in the present article, have been making their wayin the building industry for some time now, and their use will spread furtheras energy consumption containment becomes a priority.However the glazed surfaces that employ them are still expensive comparedto traditional float glass; and this higher cost is slowing their utilization.Of course the long term economic savings produced by the energyconsumption containment should easily offset the higher cost; researchindicates that the technologies can save substantial amounts of energy inbuildings, and in particular electrochromic glazings may eventually replacetraditional solar control technology such as tints, reflective films and shadingdevices.The advantages of switchable technologies are obvious as they are best suitedto adapt the thermal and visible properties of the facades to the naturalfluctuations of the environment.But the greatest expectations, of the members of the chromogenic glazedelements, are attached to the electrochromic components that can beoperated singularly by the building control system, whereas thermochromicand photochromic components respond passively collectively.The benefits of this technology can be summarized as follows: reduction of theneed of blinds and shades for solar control; optimization of the illumination

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conditions and significant lighting energy use savings if the windows are zonedand controlled properly; reduction of the cooling peak loads and of therequired HVAC capacity.

references

[1] G. Elvin, Green Technology Forum 2007, Nanotechnology for Green Building.[2] J.Bravo, , L.Zhai, Z. Wu, R.E. Cohen, M.F. Rubner, “Transparent

Superhydrophobic Films Based on Silica Nanoparticles” Langmuir 23(13): 7293-7298, 2007.

[3] A. Cavaliero, J. Th. M. De Hosson, Nanostructured Coatings, SpringerScience+Business Media, LLC, 2006.

[4] Surinder Mann, Institute of Nanotechnology., Nanoforum Report:Nanotechnology and Construction, November 2006.

[5] Y. Gogotsi, Nanomaterials Handbook, CRC press by Taylor & Francis Group, LLC,2006.

[6] H. Hohenstein, Coatings with Nano-Particles for Windows and Facades;Proceedings of Glass Processing Days – 2003.

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Summary

Preface

Giovanni Fabbrocino, Carlo Rainieri pg. 3

Chapter 1

Giovanni Fabbrocino, Carlo Rainieri

Lessons learned from monitoring of civil structures,

innovation and development of newparadigms pg. 7

Chapter 2

Yi Song, David Mast, Bolaji Suberu, Chaminda Jayasinghe,

Weifeng Li, Charles Dandino, Jandro L. Abot, Vesselin N. Shanov,

Mark J. Schulz

Basics of Carbon Nanotube Materials for Structural Applications pg. 21

Chapter 3

Yi Song, David Mast, Bolaji Suberu, Chaminda Jayasinghe,

Weifeng Li, Charles Dandino, Jandro L. Abot, Vesselin N. Shanov,

Mark J. Schulz

SHM Applications of Nanotechnologies for Sensor Development

and Communication pg. 27

Chapter 4

Paolo Corvaglia

Smart composites for S.H.M. pg. 37

Chapter 5

Livio Pascali

Cement-based smart materials pg. 51

Chapter 6

Luca Deseri, David R. Owen.

Structured deformations and the mechanics

of submacroscopically structured solids:perspectives on a new approach pg. 61

Chapter 7

Agostino Catalano

Nanotechnologies for the recovery of the concrete and composed structures pg. 73

Chapter 8

Mario Cristiano

The impact of nanoscale technologies in glazed building envelopes pg. 85

Chapter 9

Camilla Sansone

The nanotechnologies for the project and the recovery

of the natural stones and of the concrete pg. 93

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the impact of nanoscale technologies in Glazed building envelopes

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