Road Science 

Small Science Will Bring Big Changes To Roads

Nanotechnology is in its infancy, especially as a road science, but super concretes, smart aggregates, and self-healing structures are coming.

by , Contributing Editor

For millennia humans created engineered structures which used naturally available building blocks. Roman aqueducts, bridges and highways were constructed by stacking hewn blocks of stone and binding them with mortar, or by casting blocks in-place using early, naturally occurring pozzolans.

In a later era, humans made constructs, materials, or products by using chemicals or minerals, directly as found in nature, or refined. Humans bound these elements or pieces mechanically or electrochemically to make the salient features of the constructed, developed world with which we are so familiar.

Now, in the 21st century, humans are doing that mechanical/electrochemical process one better by developing the ability to create new molecules and substances from scratch, atom-by-atom, engineered layer-by-layer, each product designed with specific beneficial attributes and functions.

The scale at which these operations take place is the realm of the atom and molecule — generally, 10 times the diameter of a hydrogen atom. In terms of scientific measurement, that scale is one billionth of a meter, which is a nanometer.

That is the world of nanotechnology.

Nanotechnology and transportation infrastructure

After more than a decade of progress in other industrial sectors, the nanotechnology revolution has just begun to impact highway, road, and bridge materials and construction.

Right now, under the Federal Highway Administration’s Advanced Infrastructure Research program, study is under way on a variety of nanotechnology applications to the highway and bridge industries.

The feasibility of Cyberliths, or Smart Aggregates, as wireless sensors embedded in concrete or soil is being studied. Concrete ills such as alkali-silica reactivity and delayed ettringite formation — the bane of concrete highways and bridges — are being studied at the molecular level using neutron scattering technology and other processes.

In addition, fundamental research into the interactions between fly ash and the nanostructure of portland cement gel is under way, using neutron scattering technology. And nanotechnology is providing a close-up look at the hydration of cement grains and the nanostructure of cement reactivity as hydrated surfaces develop on individual cement grains.

But nanotechnology with application to transportation infrastructure also continues outside the government umbrella.

Autonomic (spontaneous) healing research in structural polymers, by Dr. Nancy Sottos at the University of Illinois at Urbana-Champaign, could lead the way to guardrails that heal themselves, or concrete or asphalt that heal their own cracking.

Controlled manufacture of high-performance steel at the nanotechnology level already has led to steels of incredible strength, and more is on the way.

Coatings which mimic the surface of the lotus leaf — to which nothing adheres — likely will lead to signage and work zone barricades which shed dirt and grime and never need to be washed, enhancing safety and lowering labor costs.

Microsensors, also known as MEMS (Micro-Electro-Mechanical Systems) already are in place on the Golden Gate Bridge and are giving a real-time, comprehensive picture of the bridge, with stress at any point monitored along with its impact on the rest of the bridge as a whole.

And in the future these microsensors might be reduced to dust-particle size, with the ability to coat an entire bridge with Smart Dust for optimum monitoring capabilities via a smart sensor net.

“Both asphalt and concrete are nanomaterials,” said Dr. Richard A. Livingston, senior physical scientist, at the FHWA’s Advanced Infrastructure Research program. “Up until now we haven’t clearly understood what’s going on down at that level, but what happens there affects the performance of those materials.”

Leadership at national level

“A future in which cracked bridges and potholes repair on their own, guardrails realign automatically after impact, bridges adjust their shapes to control movement caused by winds, and metal structures self-clean to avoid corrosion are among the advances in highway technology under forecast by scientists,” the FHWA reported in summer 2003.

Those prognostications followed an April 2003 workshop which brought the nation’s best thinkers on nanotechnology and transportation to the FHWA’s Turner-Fairbank Highway Research Center in McLean, Virginia.

For now, exciting, science-fiction applications such as self-healing potholes remain just tantalizing prophecies. Yet work continues in earnest, funded by both the public and private sectors. And the federal government is taking real leadership in this regard.

“Highway research and technology leads to safer, simpler, and smarter highways,” said Federal Highway Administrator Mary Peters in 2003. “The improvements we are studying can mean a better quality of life for all Americans. FHWA research engineers have an important role in advancing new technologies to serve the public and improve our nation’s highway system.”

At an April 2004 luncheon for the National Nanotechnology Initiative (NNI, www.nano.gov), Senator Ron Wyden (D-Oregon) pledged to continue working for federal funding of nanotechnology.

“Nanotechnology is going to change America on a scale equal to, if not greater than, the computer revolution,” Wyden said. “Harnessing the power of nanotechnology is one of the keys to ensuring that our nation continues to be an economic powerhouse in this new century.”

Wyden said that the U.S. nanotechnology effort should be equivalent to the effort to put a man on the moon in the 1960s. “In 2004, the idea of growing steel or highway pavement that can repair itself probably seems just as far-fetched [as was a 1969 lunar landing] to most Americans. But that’s why America needs a nanotechnology ‘moon shot’ to make America see the possibilities of nanotechnology and realize its benefits,” said Wyden.

Passage of the 21st Century Nanotechnology Research and Development Act was a major step forward. The law was signed by President Bush on December 3 and underwrites major nanotechnology efforts through 2008. That money will be channeled through the NNI into several areas, including basic nanotechnology research and development of the field’s academic and physical infrastructure.

“In addition to authorizing nearly $3.7 billion for research over the next four years,” Wyden said, “the legislation created a National Nanotechnology Program to coordinate research programs, as well as several national nanotechnology research centers to be located around the country.”

Construction behind curve

However, even as the NNI gathers momentum, the construction and materials industry remains behind other leading industries in implementing nanotechnology. In road construction and materials, maybe that’s due to the industry’s low-bid contract underpinnings and inherent reluctance to embrace new technology.

“This new, powerful, enabling technology has yet to achieve a significant impact on construction,” said Peter J.M. Bartos, director, Advanced Concrete and Masonry Centre, and Scottish Centre for Nanotechnology in Construction Materials, at the April 2003 Turner-Fairbank nanotechnology workshop.

“Application of nanotechnology in construction is still at an embryonic stage,” said Bartos. But he added that the construction industry can be a major beneficiary of nanotechnology, citing potential benefits such as advances in automation, robotization on-site, and, in the area of materials production and handling, a mixer with no moving parts, and self-compacting concrete.

He added that if nanotechnology is to make an impact in construction, the construction industry would have to do it on its own. “Due to the specific nature of construction as an industry sector, introduction and exploitation of nanotechnology in construction must be led from within,” Bartos said. “It cannot be simply transferred from other more developed industrial sectors.”

Nanotechnology defined

Nanotechnology describes research, development, and manufacture that utilizes and manipulates the unique properties of matter that exist at the nanoscale.

“At this length scale — approximately 1 to 100 nanometers — clusters of atoms and molecules exhibit properties quite different from those found at larger scales,” said Dr. Tom Mackin, associate professor, Department of Mechanical & Industrial Engineering, University of Illinois Urbana-Champaign, at the April 2003 FHWA workshop.

Thus nanoscale science and engineering is more than just what might be called hyperminiaturization. “Instead, it represents an opportunity to gain unprecedented insight into the unique phenomena that exist at the nanoscale, and to use that knowledge to engineer materials/devices with novel characteristics,” Mackin said.

With nanotechnology, super-small devices can be designed and manufactured with atomic or nanoscale precision.

“Nanotechnology is defined as fabrication of devices with atomic or molecular scale precision,” said Steve Lenhert, Quanteq, LLC, a nanotech education and networking consulting firm.

Like Mackin, Lenhert observes that at such a small scale, physical forces different from those of our human scale are at play.

“The nanoscale marks the nebulous boundary between the classical and quantum mechanical worlds,” Lenhert said. “Thus, realization of nanotechnology promises to bring revolutionary capabilities. Fabrication of nanomachines, nanoelectronics, and other nanodevices will undoubtedly solve an enormous amount of the problems faced by mankind today.”

Nanoscale of concrete

The FHWA’s Advanced Infrastructure Research program is leading research into application of nanotechnology for transportation infrastructure, having underwritten that April 2003 workshop with the U.S. Department of Transportation-funded John A. Volpe National Transportation Systems Center in Cambridge, Massachusetts.

But, more exciting than the workshop’s future-casting is what is going on now under the aegis of the Advanced Infrastructure Research program. And the bulk of that work is going into the study of concrete at a nanoscale.

Concrete is a porous material, ranging from air voids to nanometer scale pores produced by the cement-water chemical reaction, say Ken P. Chong, National Science Foundation, and Edward J. Garboczi, National Institute of Standards and Technology, in their paper Smart and Designer Structural Material Systems.

“Since these nanoscale pores control the properties of the calcium-silicate-hydrate hydration product, which is the main ‘glue’ that holds concrete together,” they say, “concrete is in some ways a nanoscale material.”

Under the assault of deicing chemicals which penetrate concrete’s porous structure and oxidize the reinforcing steel within — causing cracking and deterioration to the structure — concrete’s microstructure deserves more attention, Chong and Garboczi say.

The addition to concrete mixes of nanoscale silica fume, an industrial byproduct of glass manufacture, is being recognized as a big improvement in durability of concrete structures exposed to deicing salts (see Reclaimed Byproducts Boost Concrete Performance, Better Roads, January 2004, p 50).

“Silica fume additive operates at a nanoscale,” Livingston told Better Roads. “We know it makes for a more durable concrete, but if you put too much in, the concrete will become brittle. We need to better know how it all works together, especially now that we are adding all kinds of new materials, like ground granulated blast furnace slag, or superplasticizing chemicals. All can interact in strange ways and we need to understand quantitatively what is going on.”

Nanostructure of cement reactivity

Among the research initiatives being pursued by the FHWA is use of nuclear resonance reaction analysis to study cement hydration at a nanoscale level. The result is a better idea of what takes place on the surface of the cement particle as it hydrates, leading to improved industry standards and guidelines for mixing and curing concrete.

“We are working with [the University of Connecticut] and a group in Germany to measure how cement reacts with water on a nanoscale,” Livingston said. “We need to better know how to control the timing of concrete setting.”

The method uses a beam of nitrogen atoms to probe a reacting cement grain to locate hydrogen atoms, a necessary component of water, or its reaction products. The results of the probe are plotted in a graph called a hydrogen depth profile, which shows the rate of penetration of the water. This also indicates the arrangement of the various surface layers formed during the reaction.

The 20-nanometer-thick surface layer acts as a semi-permeable barrier that allows water to enter the cement grain and calcium ions to leach out. However, the larger silicate ions in the cement are trapped behind this layer.

As the reaction continues, a silicate gel layer forms beneath the surface layer, causing swelling within the cement grain and eventually leading to breakdown of the surface layer. This breakdown releases the accumulated silicate into the surrounding solution, where it reacts with calcium ions to form a calcium-silicate hydrate gel, which binds the cement grains together and sets the concrete. “This resolves a scientific debate that has been going on for more than a century,” Livingston said.

The evolution of the hydrogen profile shows the time of breakdown of the surface layer. This information can be used to study the concrete setting process as a function of time, temperature, cement chemistry, and other factors. For example, researchers used NRRA to determine that in cement hydrating at 86 degrees F, the breakdown occurs at 1.5 hours.

The FHWA plans to continue the NRRA research for at least two more years in collaboration with the University of Connecticut, which received a National Science Foundation grant in September 2002.

Fighting ASR on nanoscale

 The NRRA work above is only part of the concrete material research being conducted by FHWA’s Advanced Infrastructure Research program. Other ongoing projects include:

Colloidal Chemistry of Alkali-Silicate Reaction Gels. ASR occurs between alkalis from cement, and a reactive form of silica from the wrong aggregates, which can result in an alkali/silica gel. If there is enough moisture, the gel will expand, damaging the concrete.

ASR long has been thought to afflict mainly Western states, but the Strategic Highway Research Program publication, C-343 Eliminating or Minimizing Alkali-Silica Reactivity, says “the potential for deleterious ASR in highway concrete exists in every state.”

ASR weakens concrete to the point that it becomes very vulnerable to external forces, and it’s for this reason that it’s been dubbed the AIDS of concrete.

The FHWA’s work involves fundamental research into the chemical and physical processes that cause ASR gel damage. The ASR gel expansion mechanism appears to involve a phase transformation from amorphous gel to layered structure on the nanoscale, Livingston said. The research includes the application of neutron scattering and positron annihilation spectroscopy to measure nano and sub-nanoscale changes in gel microstructure as a function of gel chemistry, temperature and relative humidity.

Fly Ash Reactivity Characterization. This FHWA-funded research is a fundamental look into the interactions between fly ash, and the Portland cement gel nanostructure, that affect the strength and durability of concrete, including ASR reactivity. It includes the use of small angle neutron scattering to quantify the changes on a nanoscale as a function of time and fly ash composition. A unique vibrational spectroscopy also is being employed to nondestructively measure the reactivity of fly ashes.

Aggregate ASR Potential Tests. ASR in concrete can be precluded by using nonreactive aggregates. This FHWA research involves fundamental research into the formation of ASR gels by reaction with different types of aggregates, using solid state nuclear magnetic resonance to measure the formation of silicate chains on the nanoscale.

Delayed Ettringite Formation Damage. Delayed ettringite is an internal sulfate attack on concrete. The FHWA research is exploring how delayed ettringite forms and causes damage in concrete, in transforming from an amorphous ettringite gel to nanoscale crystals. The research involves the application of synchrotron radiation to study the relationship between ettringite crystal formation and concrete expansion.

Cement Hydration Kinetics. It’s essential to have an accurate model of the rate of reaction of cement with water as a function of temperature, water/cement ratio, and grain size, but this fundamental information has been very difficult to obtain using conventional analytical methods because the reactions take place in the nanoscale pores of the cement gel.

However, neutron scattering methods are very suitable for measuring motions and reactions of water on these length scales, Livingston said. In collaboration with the National Institute for Science & Technology’s Center for Cold Neutron Research, Turner-Fairbank researchers have been applying an array of neutron scattering methods to determine the effects of the various factors on the rate of development of cement’s fractal nanoscale structure.

Pavement, heal thyself

The idea of pavements or guard rails healing themselves after being damaged truly is the stuff of science fiction. But at the April 2003 Turner-Fairbank workshop, participants discussed using nanotechnologies to develop self-healing materials composed of molecules that are able to rejoin themselves after being cut.

Work on self-healing polymers already is under way at the University of Illinois Urbana-Champaign, by Professor Nancy Sottos and her Sottos Research Group, which has developed a structural polymeric material with the ability to autonomically heal cracks.

Autonomic (spontaneous) healing is accomplished in this program by incorporating a microencapsulated healing agent and a catalytic chemical trigger within an epoxy matrix. An approaching crack ruptures embedded microcapsules, releasing healing agent into the crack plane through capillary action. Polymerization of the healing agent is triggered by contact with the embedded catalyst, bonding the crack faces.

A similar process has been described in which microsized hollow fibers filled with crack sealant would be introduced into concrete. If the concrete cracked, the fibers would also break and release sealant. This would be especially applicable for bridge piers and columns suffering from microcracking and requiring costly epoxy injection.

And the ability to self-heal may not be limited to encapsulated microcapsules or fibers. Researcher Christian Vernet described nanoscale self-healing properties in concrete in his May 2004 article, Ultra-Durable Concretes: Structure at the Micro- and Nanoscale in the MRS Bulletin of the Materials Research Society.

“Another surprising property is the self-healing characteristic of UHPCs [ultra-high-performance concretes],” Vernet wrote. “The high fraction of anhydrous [lacking water] material left after the reaction with the water used in the initial mix is a reservoir for further hydration. When a microcrack develops, fresh anhydrous surfaces are exposed. If the sample is soaked in water, hydration starts again on these crack surfaces. The newly forming hydrates rapidly fill the crack and seal it.”

He observes that one such UHPC with fibers, Ductal, is available as a premix in the United States and Canada.

Staying clean with Lotus Effect

“Nanotechnology will lead to signs that will be able to shed water,” Livingston told Better Roads. “Existing coatings tend to accumulate grime, which reduces visibility and degrades the materials over time. Researchers have created plastic layers that have a nanoscale of roughness that will repel water and dirt, modeled after the coating of the lotus leaf.”

The lotus leaf, or water lily leaf, exhibits an extraordinary ability to keep itself clean and dry. Now nanotechnology is being used to mimic the lotus leaf surface and create new products that outperform existing no-stick products, and it’s clear that this technology will have immediate benefits for traffic and work zone signage.

Typically, on a hydrophobic (water-repellent) easy-clean surface, particles of dirt are just moved around by moving water. But on a Lotus Effect surface, dirt and grime is collected by water drops and rinses off.

At this time only one commercial product is available which utilizes this effect, an exterior house paint. But it is only a matter of time until the nanotechnology challenges are solved so that this technology can be brought to the market for use with traffic signs and, in particular, traffic control devices, which require labor-intensive, periodic washing to remove road grime and enhance visibility.

Building steel through nanotechnology

In 1992, the FHWA began partnering with the American Iron and Steel Institute and the U. S. Navy to develop new, low-carbon, high performance steel for bridges. HPS was deemed to require improved strength and weldability, and a boost in the overall quality of steels used in bridges in the United States. In 1996 the first of these steels were produced.

“Like asphalt and concrete, steel is a nanostructured material,” Livingston said. “In the low-carbon HPS steel, copper nanoparticles form at the steel grain boundaries. The resulting microstructure changes make the HPS steel tougher, easier to weld, and more corrosion-resistant.”

Separately, Sandvik Materials Technology is producing an ultra-high strength stainless steel using nanotechnology. The new product, Sandvik Nanoflex, allows ultra-high strength to be combined with good formability, corrosion resistance and a good surface finish, Sandvik says.

Because of its attributes, Nanoflex is suited to mechanical applications where lightweight, rigid designs are required, the maker says. A high modulus of elasticity combined with extreme strength can result in thinner and even lighter components than those made from aluminum and titanium. While currently being used for medical equipment, such as surgical needles and dental tools, other areas of use are anticipated. It’s not unimaginable that this technology could be applied to bridge structural elements.

Smart Aggregates and MEMS

Yet another FHWA-funded project is research on Cyberliths and their radio communications properties. This project, which is co-funded through the National Science Foundation, is studying the feasibility of using wireless sensors in highway construction materials.

Principal investigator Jennifer Bernhard of the University of Illinois Urbana-Champaign is using electromagnetic finite element models to determine the range and spatial (area) resolution of wireless sensors embedded in concrete or soil under various conditions.

In the meantime, researchers at Johns Hopkins University’s Applied Physics Laboratory have developed a robust wireless embedded sensor, suitable for long term field monitoring of corrosion in rebar, particularly in bridge decks.

These Smart Aggregates sensors can be embedded throughout a structure during concrete construction, added right to the mix before placement. The system is made up of the Smart Aggregates and a data reader that can be mounted on a car or truck. The reader powers the aggregates as it passes over them and collects the sensor data onto a PC.

Each Johns Hopkins Smart Aggregate contains wireless power receiver and data transmission coils, and is designed using ceramic hybrid integrated circuit technology to withstand mechanical stresses and the high pH environment of concrete. The aggregates are built to have a lifetime of over 50 years. The wireless power transmission and data collection approach eliminates the need for and potential problem with batteries, cables, and connectors.

Prototype Smart Aggregates have been manufactured and are undergoing reliability measurements.

Strictly speaking, while neither the Cyberliths nor the Smart Aggregate constitute nanotechnology due to their use of conventional electronics and their size (a few centimeters), they do illustrate the use of embedded sensors and give a feel for what can be accomplished in the future as this technology is reduced in size.

The future: embedded nanosensors

As a taste of what might come, in April 2003, Turner-Fairbank workshop participants discussed the potential for embedding nanosensors in road pavement to monitor processes that contribute to deterioration and cracking. The data would be accumulated in a database for researchers to use for extending the service lives of pavements. Similar sensors on bridges might monitor vibrations and loads, enabling researchers to assess structural weaknesses and conditions and fix them long before they are even apparent to human inspectors.

Another application envisioned by the workshop participants would be to improve the collection of traffic data used by transportation managers. Networks of nanosensors embedded in roadways could provide real-time information to better manage congestion and incidents, or to detect and warn drivers about fast-changing environmental conditions, such as fog and ice.

Also, the University of California-Berkeley is experimenting with MEMS they call Motes. The Golden Gate Bridge now has an experimental sensor network of approximately 200 small Motes, each with an accelerometer that measures movement such as traffic, wind, or seismic loads. When all sensor readings are correlated, a three-dimensional picture is created which may portray structural abnormalities.

From Smart Dust to ...

From Smart Aggregates, Motes, and Cyberliths, the next step down in size is theoretical Smart Dust, a Department of Defense term which describes much smaller sensors, perhaps the size of a period.

DOD Smart Dust would be distributed by air over a war zone to give planners a three- or four-dimensional visualization. They could easily go behind enemy lines, or be situated in the lairs of the enemy, providing real-time reconnaissance. Smart Dust gone awry and deadly was the nemesis in Michael Crichton’s 2002 bestselling book, Prey, now in movie production at Fox.

In the future, though, Smart Dust may have application for transportation infrastructure.

“An entire computer and strain measurement sensor system could be placed on a silicon chip, and made very small,” Livingston told Better Roads. Smart Dust incorporating minute transponders, which don’t emit radio waves until stimulated by an external signal, would eliminate the need for a bulky battery. “These fine particles could be distributed over an entire bridge structure to monitor the entire structure at once,” Livingston said.

With its progression from aggregate to motes to dust, nanotechnology for transportation infrastructure keeps getting smaller. Time will reveal just how this exciting new technology will impact our careers and the built environment around us.

For More Information

An abundance of information is available on nanotechnology, but is less abundant related to nanotechnology and transportation infrastructure. To learn more, start at these sites:

Source information on the FHWA’s vision of nanotechnology and transportation infrastructure is available at www.fhwa.dot.gov /pressroom/nanotech.htm.

Chong and Garboczi’s illuminating paper, Smart and Designer Structural Material Systems (2002), may be downloaded at http://fire.nist.gov/bfrlpubs/build03/PDF/b03006.pdf.

The Future of MEMS (in transportation engineering) is an important 18-page document released by the Transportation Research Board in October 2003. Read it at http://trb.org/publications/circulars/ec056.pdf.

The National Nanotechnology Initiative is a federal program that will drive much of U.S. nanotechnology research through the decade. Read its October 2003 update, National Nanotechnology Initiative; Research and Development Supporting the Next Industrial Revolution, at www.nano.gov/html/res/fy04-pdf/fy04-main.html.

Visit the NNI’s Web site at www.nano.gov.

A splendidly written introductory brochure on nanotechnology and nanoengineering, written for the general public and unrelated to road construction or materials, may be downloaded at www.wtec.org/loyola/nano/IWGN.Public.Brochure/IWGN.Nanotechnology.Brochure.pdf.

An online slide show on autonomic healing research is available from the University of Illinois Urbana-Champaign at www.autonomic.uiuc.edu.

The National Academy of Sciences document, Small Wonders, Endless Frontiers, is available for download at www.nano.gov/html /res/smallwonder.html.

Exciting research is under way in Germany on adaptation of the Lotus Effect via nanotechnology to real life applications. Learn more at www.botanik.uni-bonn.de/system/bionik_en.html.

A complete encyclopedia of nanotechnology may be reviewed at Quantec LLC’s Web site www.nanoword.net.

An exhaustive glossary may be explored at http://nanotech-now.com/nanotechnology-glossary.htm.

High Performance Steel Bridges. A December 2000 symposium in Baltimore brought the industry up to date on high performance steel bridges, and technical papers on fabrication and field experience among the states may be downloaded off the site to the National Bridge Research Organization, at www.nabro.unl.edu/. NaBRO is an educational/research facility at the University of Nebraska-Lincoln.

A recap of the program as of August 2003, Current Status of High Performance Steel Program is available at www.steel.org/infrastructure/pdfs/paperTRBJan2004.pdf. An early overview of the FHWA’s HPS program may be found at www.tfhrc.gov/pubrds/spring97/steel.htm.

The copper precipitation process for forming HPS described by Livingston is further explained in a .pdf at www.intlsteel.com/PDFs/products/spartan.pdf. And more information about production of high performance stainless steel through nanotechnology is available at www.azonano.com/details.asp?ArticleID=338.

Reprinted from Better Roads Magazine
July2004

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