A new type of reinforced concrete that doesn’t need any maintenance

via Inside Construction

A pedestrian bridge designed by Deakin University researchers for a North Geelong park will use a new type of reinforced concrete that doesn’t need any maintenance.

The bridge over Cowies Creek at Deppeler Park will be made from sustainable concrete with carbon and glass fibre reinforcement that should ensure the bridge requires no maintenance over its 100 year life-span.

Deakin researchers Dr Mahbube Subhani and Dr Kazem Ghabraie designed the bridge for North-Geelong based engineering firm Austeng when Austeng won a tender to build two pedestrian bridges from the City of Greater Geelong (COGG).

Dr Subhani said the new design would avoid the usual problem of corrosion that occurs in conventional steel reinforced concrete construction.

“We have replaced the steel reinforcing bar normally used in steel reinforced concrete with more durable carbon and glass fibre reinforced polymer,” Dr Subhani said.

“Structures made with steel reinforced concrete require maintenance about every five years and major maintenance or rehabilitation every 20 years.

“This bridge should not require any maintenance for the whole of its design life,” Dr Subhani said.

Carbon and glass fibre reinforced polymer is stronger than steel and five times lighter than reinforced steel.

It also needs much less energy to make – just 25 per cent of the energy required to produce steel.

“The geopolymer concrete used in the bridge construction is also environmentally sustainable,” Dr Subhani said.

“Instead of cement, the concrete has been made using fly ash, a by-product of coal combustion.

“Cement is responsible for seven per cent of the world’s total CO2 emissions so this structural element has the potential to cut down the maintenance cost as well as reduce CO2 emissions.”

The beam was cast by geopolymer concrete manufacturer, Rocla, and pre-testing has already shown the bridge can successfully carry the design load.

COGG maintains about 160 recreational bridges and that number is growing through subdivision development.

Dr Subhani and his design team hope that their environmentally sustainable maintenance-free bridge is a potential candidate for new and replacement bridges throughout the city.

Learn more: Deakin researchers design maintenance-free bridge for Geelong park

 

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Replacing Portland cement in concrete with fly ash from coal-fired power plants

A scanning electron microscope image shows raw, type C fly ash particles made primarily of calcium oxide as a byproduct of coal-fired power plants. Rice University engineers have made a cementless, environmentally friendly binder for concrete that shows potential to replace Portland cement in many applications. Courtesy of the Multiscale Materials Laboratory

Rice engineers use byproduct from coal-fired power plants to replace Portland cement

Rice University engineers have developed a composite binder made primarily of fly ash, a byproduct of coal-fired power plants, that can replace Portland cement in concrete.

The material is cementless and environmentally friendly, according to Rice materials scientist Rouzbeh Shahsavari, who developed it with graduate student Sung Hoon Hwang.

Fly ash binder does not require the high-temperature processing of Portland cement, yet tests showed it has the same compressive strength after seven days of curing. It also requires only a small fraction of the sodium-based activation chemicals used to harden Portland cement.

The results are reported in the Journal of the American Ceramic Society.

More than 20 billion tons of concrete are produced around the world every year in a manufacturing process that contributes 5 to 10 percent of carbon dioxide to global emissions, surpassed only by transportation and energy as the largest producers of the greenhouse gas.

Manufacturers often use a small amount of silicon- and aluminum-rich fly ash as a supplement to Portland cement in concrete. “The industry typically mixes 5 to 20 percent fly ash into cement to make it green, but a significant portion of the mix is still cement,” said Shahsavari, an assistant professor of civil and environmental engineering and of materials science and nanoengineering.

Previous attempts to entirely replace Portland cement with a fly ash compound required large amounts of expensive sodium-based activators that negate the environmental benefits, he said. “And in the end it was more expensive than cement,” he said.

The researchers used Taguchi analysis, a statistical method developed to narrow the large phase space — all the possible states — of a chemical composition, followed by computational optimization to identify the best mixing strategies.

This greatly improved the structural and mechanical qualities of the synthesized composites, Shahsavari said, and led to an optimal balance of calcium-rich fly ash, nanosilica and calcium oxide with less than 5 percent of a sodium-based activator.

“A majority of past works focused on so-called type F fly ash, which is derived from burning anthracite or bituminous coals in power plants and haslow calcium content,” Shahsavari said. “But globally, there are significant sources of lower grade coal such as lignite or sub-bituminous coals. Burning them results in high-calcium, or type C, fly ash, which has been more difficult to activate.

“Our work provides a viable path for efficient and cost-effective activation of this type of high-calcium fly ash, paving the path for the environmentally responsible manufacture of concrete. Future work will assess such properties as long-term behavior, shrinkage and durability.”

Shahsavari suggested the same strategy could be used to turn other industrial waste, such as blast furnace slag and rice hulls, into environmentally friendly cementitious materials without the use of cement.

Learn more: Cementless fly ash binder makes concrete ‘green

 

 

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Self-healing concrete that uses a specific type of fungi as a healing agent

Assistant professor Congrui Jin (center) with two Binghamton University graduate students from the Mechanical Engineering Department. Image Credit: Jonathan Cohen.

Binghamton University researchers have been working on a self-healing concrete that uses a specific type of fungi as a healing agent.

America’s crumbling infrastructure has been a topic of ongoing discussion in political debates and campaign rallies. The problem of aging bridges and increasingly dangerous roads is one that has been well documented and there seems to be a consensus from both democrats and republicans that something must be done.

However, spending on infrastructure improvement has continually gone down. The New York Times reported in 2016, based on a report for the Bureau of Economic Analysis, that “in the 1950s and ’60s, federal, state and local governments were spending twice as much on the nation’s public infrastructure, relative to the size of the economy, as they are today.”

The hesitancy to invest in America’s infrastructure may come from a number of sources, but the fact remains that most want something to be done before the consequences are too severe.

Binghamton University assistant professor Congrui Jin has been working on this problem since 2013, and recently published her paper “Interactions of fungi with concrete: significant importance for bio-based self-healing concrete” in the academic journal Construction & Building Materials.

This research is the first application of fungi for self-healing concrete, a low-cost, pollution-free and sustainable approach.

Why is infrastructure crumbling?

Jin’s studies have looked specifically at concrete and found that the problem stems from the smallest of cracks in the concrete.

“Without proper treatment, cracks tend to progress further and eventually require costly repair,” said Jin. “If micro-cracks expand and reach the steel reinforcement, not only the concrete will be attacked, but also the reinforcement will be corroded, as it is exposed to water, oxygen, possibly CO2 and chlorides, leading to structural failure.”

These cracks can cause huge and sometimes unseen problems for infrastructure. One potentially critical example is the case of nuclear power plants that may use concrete for radiation shielding.

What can be done?

While remaking a structure would replace the aging concrete, this would only be a short-term fix until more cracks again spring up. Jin wanted to see if there was a way to fix the concrete permanently.

“This idea was originally inspired by the miraculous ability of the human body to heal itself of cuts, bruises and broken bones,” said Jin. “For the damaged skins and tissues, the host will take in nutrients that can produce new substitutes to heal the damaged parts.”

Jin worked with associate professor Ning Zhang from Rutgers University, and professor Guangwen Zhou and associate professor David Davies from Binghamton University with support from the Research Foundation for the State University of New York’s Sustainable Community Transdisciplinary Area of Excellence Program. Together, the team set out to find a way to heal concrete.

The team found an unusual answer, a fungus called Trichoderma reesei.

When this fungus is mixed with concrete, it originally lies dormant — until the first crack appears.

“The fungal spores, together with nutrients, will be placed into the concrete matrix during the mixing process. When cracking occurs, water and oxygen will find their way in. With enough water and oxygen, the dormant fungal spores will germinate, grow and precipitate calcium carbonate to heal the cracks,” explained Jin.

“When the cracks are completely filled and ultimately no more water or oxygen can enter inside, the fungi will again form spores. As the environmental conditions become favorable in later stages, the spores could be wakened again.”

The research is still in fairly early stages with the biggest issue being the survivability of the fungus within the harsh environment of concrete. However, Jin is hopeful that with further adjustments the Trichoderma reesei will be able to effectively fill the cracks.

“There are still significant challenges to bring an efficient self-healing product to the concrete market. In my opinion, further investigation in alternative microorganisms such as fungi and yeasts for the application of self-healing concrete becomes of great potential importance,” said Jin.

Learn more: USING FUNGI TO FIX BRIDGES
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Revolutionizing the world of concrete with graphene

Innovative new ‘green’ concrete using graphene (Photo credit Dimitar Dimov)

A new greener, stronger and more durable concrete that is made using the wonder-material graphene could revolutionise the construction industry.

Experts from the University of Exeter have developed a pioneering new technique that uses nanoengineering technology to incorporate graphene into traditional concrete production.

The new composite material, which is more than twice as strong and four times more water resistant than existing concretes, can be used directly by the construction industry on building sites. All of the concrete samples tested are according to British and European standards for construction.

Crucially, the new graphene-reinforced concentre material also drastically reduced the carbon footprint of conventional concrete production methods, making it more sustainable and environmentally friendly.

The research team insist the new technique could pave the way for other nanomaterials to be incorporated into concrete, and so further modernise the construction industry worldwide.

The research is published in the journal Advanced Function Materials, on Monday, April 23 2018.

Professor Monica Craciun, co-author of the paper and from Exeter’s engineering department, said: “Our cities face a growing pressure from global challenges on pollution, sustainable urbanization and resilience to catastrophic natural events, amongst others.

“This new composite material is an absolute game-changer in terms of reinforcing traditional concrete to meets these needs. Not only is it stronger and more durable, but it is also more resistant to water, making it uniquely suitable for construction in areas  which require maintenance work and are difficult to be accessed .

“Yet perhaps more importantly, by including graphene we can reduce the amount of materials required to make concrete by around 50 per cent – leading to a significant reduction of 446kg/tonne of the carbon emissions.

“This unprecedented range of functionalities and properties uncovered are an important step in encouraging a more sustainable, environmentally-friendly construction industry worldwide.”

Previous work on using nanotechnology has concentrated on modifying existing components of cement, one of the main elements of concrete production.

In the innovative new study, the research team has created a new technique that centres on suspending atomically thin graphene in water with high yield and no defects, low cost and compatible with modern, large scale manufacturing requirements.

Dimitar Dimov, the lead author and also from the University of Exeter added: “This ground-breaking research is important as it can be applied to large-scale manufacturing and construction. The industry has to be modernised by incorporating not only off-site manufacturing, but innovative new materials as well.

“Finding greener ways to build is a crucial step forward in reducing carbon emissions around the world and so help protect our environment as much as possible. It is the first step, but a crucial step in the right direction to make a more sustainable construction industry for the future.”

Learn more: Scientists create innovative new ‘green’ concrete using graphene

 

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Incorporating irradiated plastic and fly ash into concrete for strength and reduced CO2 emissions

“Our technology takes plastic out of the landfill, locks it up in concrete, and also uses less cement to make the concrete, which makes fewer carbon dioxide emissions,” says assistant professor Michael Short.
Image: MIT News

Adding bits of irradiated plastic water bottles could cut cement industry’s carbon emissions.

Discarded plastic bottles could one day be used to build stronger, more flexible concrete structures, from sidewalks and street barriers, to buildings and bridges, according to a new study.

MIT undergraduate students have found that, by exposing plastic flakes to small, harmless doses of gamma radiation, then pulverizing the flakes into a fine powder, they can mix the irradiated plastic with cement paste and fly ash to produce concrete that is up to 15 percent stronger than conventional concrete.

Concrete is, after water, the second most widely used material on the planet. The manufacturing of concrete generates about 4.5 percent of the world’s human-induced carbon dioxide emissions. Replacing even a small portion of concrete with irradiated plastic could thus help reduce the cement industry’s global carbon footprint.

Reusing plastics as concrete additives could also redirect old water and soda bottles, the bulk of which would otherwise end up in a landfill.

“There is a huge amount of plastic that is landfilled every year,” says Michael Short, an assistant professor in MIT’s Department of Nuclear Science and Engineering. “Our technology takes plastic out of the landfill, locks it up in concrete, and also uses less cement to make the concrete, which makes fewer carbon dioxide emissions. This has the potential to pull plastic landfill waste out of the landfill and into buildings, where it could actually help to make them stronger.”

The team includes Carolyn Schaefer ’17 and MIT senior Michael Ortega, who initiated the research as a class project; Kunal Kupwade-Patil, a research scientist in the Department of Civil and Environmental Engineering; Anne White, an associate professor in the Department of Nuclear Science and Engineering; Oral Büyüköztürk, a professor in the Department of Civil and Environmental Engineering; Carmen Soriano of Argonne National Laboratory; and Short. The new paper appears in the journal Waste Management.

“This is a part of our dedicated effort in our laboratory for involving undergraduates in outstanding research experiences dealing with innovations in search of new, better concrete materials with a diverse class of additives of different chemistries,” says Büyüköztürk, who is the director of Laboratory for Infrastructure Science and Sustainability. “The findings from this undergraduate student project open a new arena in the search for solutions to sustainable infrastructure.”

An idea, crystallized

Schaefer and Ortega began to explore the possibility of plastic-reinforced concrete as part of 22.033 (Nuclear Systems Design Project), in which students were asked to pick their own project.

“They wanted to find ways to lower carbon dioxide emissions that weren’t just, ‘let’s build nuclear reactors,’” Short says. “Concrete production is one of the largest sources of carbon dioxide, and they got to thinking, ‘how could we attack that?’ They looked through the literature, and then an idea crystallized.”

The students learned that others have tried to introduce plastic into cement mixtures, but the plastic weakened the resulting concrete. Investigating further, they found evidence that exposing plastic to doses of gamma radiation makes the material’s crystalline structure change in a way that the plastic becomes stronger, stiffer, and tougher. Would irradiating plastic actually work to strengthen concrete?

To answer that question, the students first obtained flakes of polyethylene terephthalate — plastic material used to make water and soda bottles — from a local recycling facility. Schaefer and Ortega manually sorted through the flakes to remove bits of metal and other debris. They then walked the plastic samples down to the basement of MIT’s Building 8, which houses a cobalt-60 irradiator that emits gamma rays, a radiation source that is typically used commercially to decontaminate food.

“There’s no residual radioactivity from this type of irradiation,” Short says. “If you stuck something in a reactor and irradiated it with neutrons, it would come out radioactive. But gamma rays are a different kind of radiation that, under most circumstances, leave no trace of radiation.”

The team exposed various batches of flakes to either a low or high dose of gamma rays. They then ground each batch of flakes into a powder and mixed the powders with a series of cement paste samples, each with traditional Portland cement powder and one of two common mineral additives: fly ash (a byproduct of coal combustion) and silica fume (a byproduct of silicon production). Each sample contained about 1.5 percent irradiated plastic.

Once the samples were mixed with water, the researchers poured the mixtures into cylindrical molds, allowed them to cure, removed the molds, and subjected the resulting concrete cylinders to compression tests. They measured the strength of each sample and compared it with similar samples made with regular, nonirradiated plastic, as well as with samples containing no plastic at all.

They found that, in general, samples with regular plastic were weaker than those without any plastic. The concrete with fly ash or silica fume was stronger than concrete made with just Portland cement. And the presence of irradiated plastic along with fly ash strengthened the concrete even further, increasing its strength by up to 15 percent compared with samples made just with Portland cement, particularly in samples with high-dose irradiated plastic.

The concrete road ahead

After the compression tests, the researchers went one step further, using various imaging techniques to examine the samples for clues as to why irradiated plastic yielded stronger concrete.

The team took their samples to Argonne National Laboratory and the Center for Materials Science and Engineering (CMSE) at MIT, where they analyzed them using X-ray diffraction, backscattered electron microscopy, and X-ray microtomography. The high-resolution images revealed that samples containing irradiated plastic, particularly at high doses, exhibited crystalline structures with more cross-linking, or molecular connections. In these samples, the crystalline structure also seemed to block pores within concrete, making the samples more dense and therefore stronger.

“At a nano-level, this irradiated plastic affects the crystallinity of concrete,” Kupwade-Patil says. “The irradiated plastic has some reactivity, and when it mixes with Portland cement and fly ash, all three together give the magic formula, and you get stronger concrete.”

“We have observed that within the parameters of our test program, the higher the irradiated dose, the higher the strength of concrete, so further research is needed to tailor the mixture and optimize the process with irradiation for the most effective results,” Kupwade-Patil says. “The method has the potential to achieve sustainable solutions with improved performance for both structural and nonstructural applications.”

Going forward, the team is planning to experiment with different types of plastics, along with various doses of gamma radiation, to determine their effects on concrete. For now, they have found that substituting about 1.5 percent of concrete with irradiated plastic can significantly improve its strength. While that may seem like a small fraction, Short says, implemented on a global scale, replacing even that amount of concrete could have a significant impact.

“Concrete produces about 4.5 percent of the world’s carbon dioxide emissions,” Short says. “Take out 1.5 percent of that, and you’re already talking about 0.0675 percent of the world’s carbon dioxide emissions. That’s a huge amount of greenhouse gases in one fell swoop.”

“This research is a perfect example of interdisciplinary multiteam work toward creative solutions, and represents a model educational experience,” Büyüköztürk says.

This story has been updated to clarify that concrete containing both irradiated plastic and fly ash, rather than with irradiated plastic alone, is stronger, by up to 15 percent, compared to conventional concrete.

Learn more: MIT students fortify concrete by adding recycled plastic

 

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