What makes the Port at Caesarea so remarkable is the wonder-material that enabled its construction — a material known as hydraulic concrete. Hydraulic concrete is distinguished from standard concrete by the fact that it can set and harden under water. This ability is made possible by adding volcanic ash to an otherwise typical concrete mixture of limestone, clay, sand and gravel.
Concrete and other materials make possible the hard infrastructure of cities. The revolutionary soft infrastructure, ideas coupled with cutting-edge technology, is helping engineers and scientists reimagine the building materials that are creating the foundations of the smart cities of the future.
Smarter Concrete
Even more so than Rome, we have quite literally built our modern world out of concrete. It’s an amazing material ideally suited for everything from sidewalks to skyscrapers, and it keeps getting better.Perhaps the most significant innovation to concrete in recent history was the development of reinforcement. Usually made by embedding steel rebar within the concrete mixture, reinforced concrete has made possible structures of incredible strength and tensile resistance.
Presently, engineers are experimenting with reinforcing concrete using different materials, including steel fibers, plastics and even glass. Newer, stronger versions of concrete make innovative building solutions feasible, such as constructing homes and office buildings using insulated concrete forms (ICF).
Cities that aim to reduce the energy footprint of new construction are starting to take a serious look at ICF.
According to the Portland Cement Association (PCA), “A major appeal of ICFs is the potential for reducing energy to heat and cool the building. Some estimates place the savings at 20 percent or more. As a result, assuming a 100-year service life, one single-family ICF home has the potential to save about 110 tons of CO2 compared to a traditional wood frame home.”
However, anyone who has ever attempted to pour a new patio or driveway knows concrete is an expensive material. Due to the many advantageous characteristics of ICFs, including making construction quicker and easier, a structure made using ICFs is not significantly more expensive than a traditional counterpart. According to PCA, “using ICFs adds about 3 percent to overall construction costs compared with a conventional wood-frame building.”
“ICF is a very good system,” said Ali Memari, professor of Architectural and Civil Engineering at Penn State. “For residential buildings it is an excellent system. Pricewise, you can’t beat wood but for areas that are susceptible to hurricanes and tornados, then yes it’s a very good idea.”
Blending new reinforcing materials into concrete to enhance its resiliency has led to some unexpected discoveries. Deborah D.L. Chung, director of the Composite Materials Research Laboratory at the University of Buffalo, created and patented what she calls “smart concrete.” Chung found that adding carbon fibers to the mixture results in a concrete that is conductive when an electric current is applied.
“The fibers can greatly affect the electrical properties,” Chung explained in a video about smart concrete produced by NBC and the National Science Foundation, “not only making it more conductive but making it able to have its electrical resistance change in response to damage or defamation. And that makes the concrete a sensor.”
By attaching a meter to smart concrete, engineers can gather real-time data about the stress being placed on a structure built with the material. Increased stress or pressure changes the conductive properties of the concrete, allowing for predictive analysis of the structural integrity that can warn of impending problems.
The process is similar to the body’s blood clotting ability. In fact, researchers at the University of Illinois stated in a paper titled Self-Healing Polymers and Composites that self-healing concrete is based on natural phenomena.
“Self-healing polymers and fiber-reinforced polymer composites possess the ability to heal in response to damage wherever and whenever it occurs in the material. This phenomenal material behavior is inspired by biological systems in which self-healing is commonplace.”
Concrete may be an ancient building material, but continuing advancements point to a bright and smarter future.
Wood You Believe?
In March 2014, U.S. Department of Agriculture Secretary Tom Vilsack announced that engineers and architects at the USDA would receive training on the designing and building of taller structures composed of wood.While common in homes, wood doesn’t find its way into many structures taller than a couple of stories. Historically, builders preferred the proven strength of concrete and steel when building skyscrapers. New science and manufacturing processes are changing these beliefs.
In many cities around the world there will soon exist seemingly ordinary buildings that are anything but. In Milan; Portland, Ore.; Vancouver; Stockholm and London there are plans for skyscrapers up to 34 stories tall with a structural skeleton made of wood.
Why wood? For one thing it’s an extremely strong material. It also sequesters carbon dioxide, unlike concrete, which emits massive amounts of carbon dioxide as part of its production. Wood is also, when managed correctly, a renewable resource.
Driving the wood revival is a highly touted manufactured wood product called cross-laminated timber (CLT). According to the APA — The Engineered Wood Association, “CLT is becoming increasingly popular as an alternative to conventional structural materials” thanks to its relatively low weight, strength, seismic performance, versatility and environmental friendliness.
But what about fire? Municipal building code limits the height of wooden structures due to fire danger. In a typical home, for example, the wood framing is erected in a single layer with many gaps. But the density of CLT actually creates a wood product that is fire resistant.
“When you’re trying to light a fire in your house, you don’t start with a log,” CLT expert Craig Liddell told The New York Times in a 2012 article. “You start with kindling. You could be hours getting that log to light.”
Back at the USDA, Vilsack said the agency, along with the Binational Softwood Lumber Council, are investing $2 million in a wood-building competition.
Speaking with The Oregonian, Vilsack said, “We’re trying to incent people to think differently and overcome the barriers that may exist at first glance.”
It seems that smart cities of the future may, at least in part, be built using the world’s oldest construction material.
Through the Looking Glass
Glass has been a common building block for millennia. Today, buildings of every size and shape are often sheathed entirely in this strong and versatile yet brittle material. But glass is changing — it’s becoming stronger, more durable and much smarter.Based on a technology that enables eyeglasses to automatically tint themselves, a number of companies are attempting to apply this same technology to entire buildings.
Often called “dynamic glass,” companies including View Inc., Sage Electrochromics and SmartGlass International are developing glass that tints itself based on light intensity. This process is known as photochromism, wherein a material changes its properties when light is introduced. Similar processes include electrochromism and thermalchromism.
“With different coatings that we can add to the glass we can add a lot of different functions to the glazing system,” Penn State’s Memari said. “Photochromic, electrochromic, thermalchromic, these will change the visibility of the glass. We have coatings that prevent the heat from solar light — the glass will reflect the heat from solar light and only let in visible light. And we can use glass and the coatings as insulation.”
Dynamic glass manufacturers claim this technology can reduce energy costs in buildings by up to 20 percent. That’s a remarkable number considering the fact that buildings are responsible for about 40 percent of the industrialized world’s energy consumption.
Generally, dynamic glass works by incorporating layers of electrochromic materials — often specialized types of ceramics — that are either passively controlled based on light or actively controlled by a user. Some companies are developing films that can be applied to existing windows to replicate the dynamic glass experience.
“We’ve been laboring away at this for six years,” said Rao Mulpuri, CEO of View Inc., in March 2014 at the Forbes Reinventing America Summit. “The problem with windows is sometimes you have too much heat and too much light coming through.”
Mulpuri noted a recent study that found that 59 percent of all the window surfaces in New York City are covered with blinds — proving his point that windows allow too much heat and light to seep through. He also said Boeing deployed dynamic glass in the windows of its new Dreamliner passenger jet to help reduce the amount of light and heat allowed into the plane.
“So it’s not farfetched that you could have a building window that does that,” he said. “You can program this such that it is able to intelligently and on demand change the condition of the building to your liking.”
Concrete, wood and glass — all discoveries of the ancient world and all of which will continue to serve us, with a bit more technology added in, as we build the hard infrastructure of the smarter cities of the future.
Editor's note: This feature originally appeared in the November 2014 print edition of FutureStructure, a sister publication to Government Technology. You can download the issue here.
