New concrete to reduce time needed for road works by more than half
Nanyang Technological University (NTU Singapore) scientists from the NTU-JTC Industrial Infrastructure Innovation Centre (I³C) have invented a new type of concrete called ConFlexPave that is bendable yet stronger and longer lasting than regular concrete which is heavy, brittle and breaks under tension.
This innovation allows the creation of slim precast pavement slabs for quick installation, thus halving the time needed for road works and new pavements. It is also more sustainable, requiring less maintenance.
NTU Professor Chu Jian, Interim Co-Director of the NTU-JTC I³C, said, “We developed a new type of concrete that can greatly reduce the thickness and weight of precast pavement slabs, hence enabling speedy plug-and-play installation, where new concrete slabs prepared off-site can easily replace worn out ones.”
Mr Koh Chwee, Director, Technical Services Division of JTC and Co-Director of the NTU-JTC I3C, said that the invention of this game-changing technology will not only enable the construction industry to reduce labour intensive on-site work, enhance workers’ safety and reduce construction time, it also benefits road users by cutting down the inconvenience caused by road resurfacing and construction works.
“Through collaborations with universities such as NTU in research and development of disruptive technologies, JTC hopes to pioneer cutting-edge industrial infrastructure solutions to address challenges faced by Singapore and its companies such as manpower and resource constraints. We will continue to open up more of our buildings and estates to test-bed and if successful, implement such new solutions,” Mr Koh added.
How bendable concrete works
Typical concrete comprises cement, water, gravel and sand. While this mixture makes concrete hard and strong, it does not promote flexibility. Thus concrete is brittle and prone to cracks if too much weight is applied.
ConFlexPave is specifically engineered to have certain types of hard materials mixed with polymer microfibres. The inclusion of these special synthetic fibres, besides allowing the concrete to flex and bend under tension, also enhances skid resistance.
The key breakthrough was understanding how the components of the materials interact with one another mechanically on a microscopic level, said Asst Prof Yang En-Hua from NTU’s School of Civil and Environmental Engineering who leads this research at the NTU-JTC I³C.
“With detailed understanding, we can then deliberately select ingredients and engineer the tailoring of components, so our final material can fulfill specific requirements needed for road and pavement applications,” explained Prof Yang.
“The hard materials give a non-slip surface texture while the microfibres which are thinner than the width of a human hair, distribute the load across the whole slab, resulting in a concrete that is tough as metal and at least twice as strong as conventional concrete under bending,” he added.
Mortar with an added bacterial film is highly resistant to water uptake
Moisture can destroy mortar over time – for example when cracks form as a result of frost. A team of scientists at the Technical University of Munich (TUM) has found an unusual way to protect mortar from moisture: When the material is being mixed, they add a biofilm – a soft, moist substance produced by bacteria.
Oliver Lieleg usually has little to do with bricks, mortar and concrete. As a professor of biomechanics at the Institute of Medical Engineering (IMETUM) and the Department of Mechanical Engineering, he mainly deals with biopolymer-based hydrogels or, to put it bluntly, slime formed by living organisms.
These include bacterial biofilms, such as dental plaque and the slimy black coating that forms in sewage pipes. “Biofilms are generally considered undesirable and harmful. They are something you want to get rid of,” says Oliver Lieleg. “I was therefore excited to find a beneficial use for them.”
INSPIRATION FROM A CONVERSATION
During a conversation with a colleague at TUM, Lieleg came up with the idea of using biofilms to alter the properties of construction materials. Professor Christian Große holds the Chair of Non-destructive Testing. Among other things, he investigates self-healing concrete whose cracks close autonomously. One variant of this concrete contains added bacteria. Activated by the ingress of moisture, the bacteria close the cracks with metabolic products containing calcium.
For his own project, Lieleg used mortar instead of concrete. Instead of mending cracks after damage has occurred, he wants to prevent moisture from penetrating into mortar in the first place. Such invading water can cause serious problems, for example by inducing the growth of mold or widening existing microcracks through freeze-thaw-cycles. To prevent such water ingress, he takes advantage of the fact that some bacterial films are highly water-repellent. In the journal Advanced Materials, Lieleg and his colleagues describe how to make a moisture-resistant hybrid mortar.
A SOIL BACTERIUM PRODUCES THE BIO-SUPPLEMENT
The key ingredient in the new material is biofilm produced by the bacterium Bacillus subtilis. “Bacillus subtilis normally lives in soil and is very common microorganism,” Oliver Lieleg explains. “For our experiments, we used a simple laboratory strain that grows rapidly, forms plenty of biomass and is completely harmless.” Lieleg’s team bred the bacterial film on standard culture media in the lab. They then added the moist biofilm to the mortar powder.
In the generated hybrid mortar, water was significantly less able to wet the surface compared to untreated mortar. To evaluate this surface property, the scientists measured the contact angle between water droplets and the surface. The steeper this angle, the more spherical the drops are, and the less likely the liquid is soaked into the material. Whereas this angle is only 30 degrees or less on untreated mortar, it is three times as high for drops on the hybrid mortar. Water droplets on polytetrafluoroethylene, better known by the trade name “Teflon”, have a similarly high contact angle.
NANOSTRUCTURES IN THE MORTAR
An explanation for the water-repellent properties of the hybrid mortar can be found in electron microscope images: The surface is covered with tiny crystalline spikes. This results in what is known as the lotus effect, which also occurs on the leaves of the lotus plant. The small uniform structures on the surface ensure that only a small part of a water droplet is actually in contact with the leaf surface. The surface tension of the droplet therefor is stronger than the forces that make it adhere to the leaf. Consequently, the droplet easily rolls off the leaf when the leaf is tilted. A cross-section of hybrid mortar shows that crystalline spikes are not only evenly distributed on the mortar surface but can also be found throughout the bulk volume of the mortar. This reduces the capillary forces that are normally responsible for the uprise of water in mortar when the material is immersed into liquid.
Although similar spikes also occur on untreated mortar, they are too long, rare and scattered for the lotus effect to occur. The researchers assume that the added biofilm stimulates uniform crystal growth throughout the volume of the hybrid material.
To find out if the hybrid mortar is resistant enough to actually be used in construction applications, it is currently undergoing mechanical tests in Christian Grosse’s department. “If the mortar is in fact suitable, there should be no problem for companies to produce it on a large scale,” Oliver Lieleg says. Both the bacterial strain used and the culture media are standard and relatively inexpensive. “We‘ve also discovered in our experiments that freeze-dried biofilm can be used equally well. Then, in a powder form, the biological material can be stored, transported and addedmuch more easily .” In the future, the scientists want to examine whether the biofilm can also be used to protect concrete against water.
Researchers look to bones and shells as blueprints for stronger, more durable concrete.
Researchers at MIT are seeking to redesign concrete — the most widely used human-made material in the world — by following nature’s blueprints.
In a paper published online in the journal Construction and Building Materials, the team contrasts cement paste — concrete’s binding ingredient — with the structure and properties of natural materials such as bones, shells, and deep-sea sponges. As the researchers observed, these biological materials are exceptionally strong and durable, thanks in part to their precise assembly of structures at multiple length scales, from the molecular to the macro, or visible, level.
From their observations, the team, led by Oral Buyukozturk, a professor in MIT’s Department of Civil and Environmental Engineering (CEE), proposed a new bioinspired, “bottom-up” approach for designing cement paste.
“These materials are assembled in a fascinating fashion, with simple constituents arranging in complex geometric configurations that are beautiful to observe,” Buyukozturk says. “We want to see what kinds of micromechanisms exist within them that provide such superior properties, and how we can adopt a similar building-block-based approach for concrete.”
The new building material could transform polluting emissions into a valuable resource
Imagine a world with little or no concrete. Would that even be possible? After all, concrete is everywhere — on our roads, our driveways, in our homes, bridges and buildings. For the past 200 years, it’s been the very foundation of much of our planet.
But the production of cement, which when mixed with water forms the binding agent in concrete, is also one of the biggest contributors to greenhouse gas emissions. In fact, about 5 percent of the planet’s greenhouse gas emissions comes from concrete.
An even larger source of carbon dioxide emissions is flue gas emitted from smokestacks at power plants around the world. Carbon emissions from those plants are the largest source of harmful global greenhouse gas in the world.
A team of interdisciplinary researchers at UCLA has been working on a unique solution that may help eliminate these sources of greenhouse gases. Their plan would be to create a closed-loop process: capturing carbon from power plant smokestacks and using it to create a new building material — CO2NCRETE — that would be fabricated using 3D printers. That’s “upcycling.”
“What this technology does is take something that we have viewed as a nuisance — carbon dioxide that’s emitted from smokestacks — and turn it into something valuable,” said J.R. DeShazo, professor of public policy at the UCLA Luskin School of Public Affairs and director of the UCLA Luskin Center for Innovation.
“I decided to get involved in this project because it could be a game-changer for climate policy,” DeShazo said. “This technology tackles global climate change, which is one of the biggest challenges that society faces now and will face over the next century.”
DeShazo has provided the public policy and economic guidance for this research. The scientific contributions have been led by Gaurav Sant, associate professor and Henry Samueli Fellow in Civil and Environmental Engineering; Richard Kaner, distinguished professor in chemistry and biochemistry, and materials science and engineering; Laurent Pilon, professor in mechanical and aerospace engineering and bioengineering; and Matthieu Bauchy, assistant professor in civil and environmental engineering.
This isn’t the first attempt to capture carbon emissions from power plants. It’s been done before, but the challenge has been what to do with the carbon dioxide once it’s captured.
“We hope to not only capture more gas,” DeShazo said, “but we’re going to take that gas and, instead of storing it, which is the current approach, we’re going to try to use it to create a new kind of building material that will replace cement.”
“The approach we are trying to propose is you look at carbon dioxide as a resource — a resource you can reutilize,” Sant said. “While cement production results in carbon dioxide, just as the production of coal or the production of natural gas does, if we can reutilize CO2 to make a building material which would be a new kind of cement, that’s an opportunity.”
The researchers are excited about the possibility of reducing greenhouse gas in the U.S., especially in regions where coal-fired power plants are abundant. “But even more so is the promise to reduce the emissions in China and India,” DeShazo said. “China is currently the largest greenhouse gas producer in the world, and India will soon be number two, surpassing us.”
Thus far, the new construction material has been produced only at a lab scale, using 3-D printers to shape it into tiny cones. “We have proof of concept that we can do this,” DeShazo said. “But we need to begin the process of increasing the volume of material and then think about how to pilot it commercially. It’s one thing to prove these technologies in the laboratory. It’s another to take them out into the field and see how they work under real-world conditions.”
“We can demonstrate a process where we take lime and combine it with carbon dioxide to produce a cement-like material,” Sant said. “The big challenge we foresee with this is we’re not just trying to develop a building material. We’re trying to develop a process solution, an integrated technology which goes right from CO2 to a finished product.
“3-D printing has been done for some time in the biomedical world,” Sant said, “but when you do it in a biomedical setting, you’re interested in resolution. You’re interested in precision. In construction, all of these things are important but not at the same scale. There is a scale challenge, because rather than print something that’s 5 centimeters long, we want to be able to print a beam that’s 5 meters long. The size scalability is a really important part.”
Another challenge is convincing stakeholders that a cosmic shift like the researchers are proposing is beneficial — not just for the planet, but for them, too.
“This technology could change the economic incentives associated with these power plants in their operations and turn the smokestack flue gas into a resource countries can use, to build up their cities, extend their road systems,” DeShazo said. “It takes what was a problem and turns it into a benefit in products and services that are going to be very much needed and valued in places like India and China.”