Concrete

Researchers explore strategies to 'bury' CO2 in concrete buildings

Christopher.Sorensen — Fri, 02 Dec 2022 18:11:32 +0000

Researchers explore strategies to 'bury' CO2 in concrete buildings

Christopher.Sorensen Fri, 12/02/2022 - 13:11

Cutline

Samples of concrete cure in a carbonation chamber in the lab of Daman Panesar, a professor in U of T's Faculty of Applied Science & Engineering (photo by Dr. Runxiao Zhang)

Tyler Irving

Topic

Breaking Research

Climate Change

Concrete

Faculty of Applied Science & Engineering

Research & Innovation

Sustainability

One of the most powerful tools for mitigating the impact of climate change could be a material that is so common we tend not to think about it very much – concrete.

The world’s most widely used building material, concrete has an impact on carbon emissions – both as a burden and a benefit. The production of cement – one of the key components of concrete – produces relatively large amounts of carbon emissions, so mitigating these could make a big difference. But over its lifetime, concrete also has the ability to uptake carbon from the air.

Now, a new collaboration between a team of researchers led by Daman Panesar, a professor in the University of Toronto’s department of civil and mineral engineering in the Faculty of Applied Science & Engineering, and the Canada Green Building Council (CAGBC) will identify the potential and implications of low-carbon approaches and technologies and how they might capture large amounts of CO2 and trap it in concrete.

“Burying Carbon in Buildings: Advancing Carbon Capture and Utilization in Cementitious Building Materials” is funded by a recently-announced $1.7 million contribution by the Government of Canada.

Professor Daman Panesar

“Currently, several low-carbon concrete framework documents have been produced worldwide and most of these roadmaps have set 2050 carbon reduction targets related to several levers, such as clinker-cement ratio, alternative fuel use and carbon capture, storage and sequestration,” says Panesar.

While there has been preliminary work on several carbon utilization approaches, few have been implemented on a large scale. Panesar and her team will examine the challenges associated with scale-up of these strategies and explore new technologies that can effectively turn built infrastructure into a carbon sink.

“Natural carbonation of concrete occurs by a chemical reaction between the constituents of concrete, particularly cement, and atmospheric carbon dioxide – and it has the potential to occur throughout the life of the concrete,” says Panesar.

“However, accelerated or enforced carbonation approaches are relatively new technologies, which can also be referred to as carbon capture and utilization technologies, and can be introduced at different life stages such as during manufacture or at end-of-life.”

Some examples of carbonation processes that will be explored and assessed include: CO2 injection, elevated CO2 exposure, mineral carbonation using recycled or waste CO2, industry by-products used to replace cement and subsequent CO2 curing, as well as the potential for synthetic treated aggregates.

“All of these techniques need further understanding of the implications and potential for negative emission technologies such as carbon capture utilization approaches,” Panesar says.

Another challenge for both new and existing structures is ensuring that any change to the formulations of concrete – for example, using lower-carbon components or absorbing more CO2 during curing – doesn’t come at the expense of its required structural and material design properties, including strength and durability.

“For example, considering natural carbonation processes, the mechanism related to the potential for increased vulnerability of reinforced concrete elements to steel corrosion, concrete degradation and shortened service lives is fairly well understood.” says Panesar.

“For existing infrastructure, the situation becomes more complex because there is a need to account for and interpret the role of age-related cracking on the CO2 uptake of concrete, as well as in conjunction with other predominant degradation issues in Canada, such as freeze-thaw cycles.”

Finally, researchers will need to develop benchmarks and other standardized tools to accurately account for the carbon uptake in building materials.

“Currently, there is no harmonized measure of concrete carbonation and the differences in measurements and reporting add an extra dimension of complexity when trying to compare between different concrete formulations and/or CO2 uptake technologies,” says Panesar.

“Carbon accounting is critical to enable us to determine the relative environmental impacts of the various approaches and to be able to estimate or forecast the impacts of deploying these new technologies in the coming decades.”

One of the strengths of the new collaboration is that it provides a built-in pathway for new research findings to get translated into industry, as well as into new policies and regulations.

“As the national organization representing members and stakeholders across the green building spectrum, CAGBC can access industry expertise to help advance research and mobilize the sector to implement market solutions,” says Thomas Mueller, president and CEO of the Canada Green Building Council.

“We are proud to partner with the University of Toronto on a project that has the potential to significantly reduce embodied carbon emissions from the cement industry. The results will contribute to the collective effort to decarbonize construction.”

U of T Engineering professor on a mission to lower concrete’s carbon footprint

Christopher.Sorensen — Mon, 18 Oct 2021 17:08:43 +0000

U of T Engineering professor on a mission to lower concrete’s carbon footprint

Christopher.Sorensen Mon, 10/18/2021 - 13:08

Cutline

Research by U of T Engineering Professor Doug Hooton shows that a few simple substitutions can cut the carbon footprint of concrete in half (photo by twenty20photos via Envato Elements)

Tyler Irving

Topic

Our Community

Concrete

Faculty of Applied Science & Engineering

Sustainability

For Douglas Hooton, the main challenge of building sustainably with concrete isn’t really the chemistry or the engineering – it’s trust.

Doug Hooton

“Construction is a very conservative industry, and it’s very decentralized,” says Hooton, a professor emeritus in the department of civil and mineral engineering in the Faculty of Applied Science & Engineering.

“You have building owners, architects, structural engineers, contractors and their [tradespeople]. None of them want to increase their risk by doing something different from what’s been done before.”

Yet, for more than a decade, Hooton and his team have been demonstrating that a few simple adjustments to the formulation of concrete can significantly reduce its environmental impact without affecting its cost or performance.

They have conducted extensive field trials and Hooton has even written standards to encourage the use of these modified materials.

But it has been slow going.

“All of this stuff is really just the low-hanging fruit,” he says. “You’d think it would be a no-brainer, but it isn’t.”

The challenge with concrete starts with the chemistry of one of its key ingredients: Portland cement. To make it, producers mix limestone – which is mostly calcium carbonate – with various clay minerals and process it through a kiln at very high temperatures. In the kiln, the calcium loses its carbon, which is driven off as carbon dioxide gas, and then combines with silica, alumina and other elements in the clay to create clinker – the precursor to cement. Portland cement is then made by grinding clinker together with gypsum into a fine power.

The CO2 gas emitted during the kiln reactions, combined with emissions from burning fossil fuels to heat the kiln, mean that for every kilogram of cement clinker produced, a nearly equivalent mass of CO2 is emitted.

In this 2010, then-graduate student Reza Ahani prepares concrete samples made with various formulations for testing (photo courtesy of Doug Hooton)

One way to address the challenge is to change the formulations of the cementing materials to lower their carbon footprints. Hooton has championed national and international standards for a material known as Portland-limestone cement, which replaces up to 15 per cent of the final cement powder with ground raw limestone.

The resulting material is a drop-in replacement for Portland cement in concrete, and is able to meet the same performance standards – as Hooton has shown through laboratory experiments and field trials.

“For example, one of the concerns that has been raised is the idea that this type of cement might be susceptible to attack by sulphates,” Hooton says. “Sulphate minerals are common in soils in Western Canada and can degrade some types of concrete if they are not designed for it.”

Through the NSERC/Cement Association of Canada Industrial Research Chair in Concrete Durability and Sustainability, Hooton initiated a field trial that has been running for 11 years. His team cast more than 1,000 beams of concrete – some made with traditional Portland cement and others made with Portland-limestone cement. All the beams were then exposed to aggressive sulphate solutions.

“We take them out and look at them every year,” he says. “The ones made with Portland-limestone cement are fine – in fact they’re actually performing better than many traditional concretes that have been specifically designed to stand up to sulphates.”

In addition to pure limestone, Hooton and his team have also tested other potential cement clinker replacements for use in concrete. One of these is a substance known as blast furnace slag, a waste product of the iron and steel industry, which can be mixed with either Portland cement and Portland-limestone cement at levels of up to 75 per cent. This cuts the overall amount of cement used, lowering emissions proportionally.

“A switch to Portland-limestone cement, followed by a substitution of 35 to 40 per cent slag would cut the carbon footprint of the resulting concrete by about half,” says Hooton.

Hooton says that one of the concerns about using slag is that, at high replacement levels, it slows down the time it takes for the concrete to gain strength. This affects the early-age strength required to allow different construction operations, though the final strength is the same.

“We build structures to last 100 years – not just a few weeks,” he says. “So, the final strength, which you reach at about 90 days, is what matters. On that timeline, we’ve shown that blast furnace slag mixed with Portland-limestone cement actually works better than with Portland cement because of reactions that happen between carbon in the limestone and alumina compounds in the slag.”

To deal with the early-age strength issue, Hooton and his team have done research on advanced testing methods. Currently, most standards for cement and concrete are based on testing the strength of the material after 28 days.

While this is sufficient time for traditional Portland cement to develop its properties, some cement replacements can lengthen this timeline. Those who oversee concrete specifications are resistant to adopting new protocols that will take two or three times as long as those they are used to, according to Hooton.

“We can accelerate the testing process by increasing concrete temperature,” says Hooton. “It’s not rocket science, and we’ve known how to do it for decades. If we can give you a good indicator at 28 days of what’s going to happen at 90 days, it might grease the wheels in terms of getting these alternative materials more widely adopted.”

Hooton’s views and evidence carry weight since he serves as the chair of the CSA Group’s committee on concrete materials and methods of concrete construction and is the chair of the durability of concrete committee of the American Concrete Institute. He is also the chair of the ASTM International (formerly known as American Society for Testing and Materials) committee on cements.

But he points out that simply creating standards is not enough to have lower-carbon footprint materials used in practice. To this end, he recently partnered with a team of experts on a new initiative aimed at identifying the barriers to rapid adoption of carbon reduction technologies in the North American concrete industry.

The collaboration includes Thomas Van Dam of NCE, an American engineering consulting firm, Professor Larry Sutter of Michigan Technological University and Al Innis, a former vice-president of quality at Lafarge-Holcim, one of the world’s leading manufacturers of building materials.

“In phase one of this project, we’re looking at the overall flows of cements, from where it’s produced to where it’s utilized, and identifying the barriers to adoption of more sustainable cementitious materials at each point along that chain,” Hooton says.

“After that, we’re going to be developing a plan to systematically address those barriers. What we’re looking for are the big plays, including the places where some education and technology transfer will increase trust of the various parties in construction and make the most impact. And I’m optimistic we’ll find them.”

U of T partners with Indian researchers to develop safer, earthquake resistant buildings

ullahnor — Mon, 27 Feb 2017 15:05:51 +0000

U of T partners with Indian researchers to develop safer, earthquake resistant buildings

ullahnor Mon, 02/27/2017 - 10:05

Cutline

Schematics of two reinforced concrete buildings designed according to current Indian standards. A research collaboration between U of T and IIT Bombay hopes to develop buildings that can withstand earthquakes (image by IIT Bombay/Farbod Pakpour)

Tyler Irving

Author legacy

Tyler Irving

Topic

Breaking Research

Faculty of Applied Science & Engineering

Buildings

Concrete

Earthquakes

Two new collaborations between researchers at U of T's Faculty of Applied Science & Engineering and the Indian Institute of Technology Bombay (IIT Bombay) hopes to improve the safety, resilience and sustainability of buildings in both countries.

The two projects are:

India-Canada Initiative for Resilient Global Urban Shelter – A partnership between U of T's Professor Constantin Christopoulos and IIT Bombay's Professor Ravi Sinha, this project focuses on low-cost seismic isolation platforms to help buildings withstand earthquakes.
Smart Sensor Deployment in Buildings: Evacuation Planning and Energy Management - Led jointly by U of T's Professor Mark Fox and IIT's Professor Krithi Ramamritham, this project leverages a network of sensors within buildings to optimize energy use and emergency evacuation plans.

Both projects recently received funding from IC-IMPACTS, a Canadian Network Centre of Excellence that brings communities together with academia, industry and government to develop solutions to key challenges in both India and Canada.

These projects reflect the goals of India’s Smart Cities Mission, a major urban renewal and retrofitting program taking place in more than one hundred cities across the subcontinent.

“Where there is mass development, there is a lot of opportunity to implement new technologies,” says Christopoulos.

The Structural Engineering Laboratory at U of T contains advanced equipment to test prototypes of building components, including a proposed low-cost seismic isolation platform for mass implementation in India (photo by Farbod Pakpour)

Resilient urban infrastructure

Christopoulos says that the earthquakes that rocked Christchurch, New Zealand, in 2010 and 2011 killed far fewer people than the catastrophic January 2010 quake off the coast of Haiti, and that's because of superior building codes and construction regulations in New Zealand, designed to save lives. Yet imposing, implementing and enforcing those regulations can be difficult in developing countries.

“To have a major impact on the entire ecosystem – manufacturers of materials, engineers, local contractors, inspectors – takes tremendous effort and a lot of time,” says Christopoulos.

While modern construction ensured that most of Christchurch’s buildings did not fall, many were still severely damaged.

“Eighty per cent of the taller buildings in their business district had to be demolished,” says Christopoulos. “They are predicting that it will take more than a decade to recover.”

Christopoulos and his team study how to protect buildings from this kind of damage by isolating the structure from the ground. The method, called seismic isolation, involves introducing a flexible layer such as ball bearings or specially designed sliders, under or within the building.

“When the earthquake occurs, the building doesn’t really feel it,” says Christopoulos.

Currently, seismic isolation is costly and tends to be implemented in only high-end buildings, such as Apple’s Cupertino headquarters, or those that house essential services such as hospitals. Now, Christopoulos aims to design a simple, low-cost isolation platform for ordinary buildings that could be adopted on a massive scale in developing countries like India. His team is collaborating with Sinha at IIT Bombay to create computer models that could test this type of intervention using data from real Indian buildings.

“The idea is not to change the entire construction ecosystem but to have only one additional, highly engineered interface that could be checked and controlled,” says Christopoulos.

For example, certain types of commercially available plastic, laid down under a concrete column, might provide the sliding capacity to absorb the earthquake energy while protecting the building sitting on top of it.

Once the best materials are identified, they will be incorporated into prototypes and tested in full-scale and in real time in the Structural Engineering Laboratory at U of T Engineering. The two teams will then work together on a mass implementation plan.

“Here in Canada, our buildings are only being replaced at an incremental rate,” says Christopoulos. “By pairing with a country like India, where there is mass development, we have a chance to create lots of buildings with significantly more resilience than our own. In the long run, we will be looking at re-importing the technology for mass implementation back to Canada.”

Energy conservation? Fire? There’s an app for that

Air conditioning is expensive, especially as most rooms are unoccupied for much of the day. Fox and Ramamritham want to create a more intelligent system to better match energy consumption to specific demand in individual rooms.

Ramamritham and his team have equipped a building on the IIT Bombay campus with an array of sensors that detect the infrared light given off by hot objects. Not only do these devices measure the average temperature of the room, they can also detect the presence of people.

Ramamritham will provide the sensor data to Fox and his team, who will use it to build a piece of software known as a semantic model.

“We need to be able to represent the building, the sensors, the pathways and the state of all of these components,” says Fox.

The model is run on a central server, and users can interact with using external devices such as smartphone apps. The model can use past behaviour to make intelligent predictions about future behaviour. For example, if someone arrives early each morning, the app would notice and cool their office ahead of their arrival. Likewise, if a room is never used on Fridays, the app could shut off the air conditioning, saving valuable energy.

This type of adaptive, predictive system would also be useful in the event of a fire or other emergency.

“Evacuation maps already exist, but they don’t tell you if an exit is blocked,” says Fox. “A smartphone app, connected to our semantic model, could provide real-time information.”

By providing users with the most up-to-date escape routes, the app could prevent damage and save lives.

Concrete checkup: U of T engineering researcher develops diagnostics for bridges, buildings, roads

ullahnor — Fri, 17 Feb 2017 19:43:28 +0000

Concrete checkup: U of T engineering researcher develops diagnostics for bridges, buildings, roads

ullahnor Fri, 02/17/2017 - 14:43

Cutline

Assistant Professor Fae Azhari's work helps monitor the structural health of crucial infrastructure such as bridges, roads and hydroelectric dams (photo by Roberta Baker)

Marit Mitchell

Author legacy

Marit Mitchell

Topic

Breaking Research

Faculty of Applied Science & Engineering

Canada will spend $125 billion on infrastructure maintenance and expansion in the next 10 years. Assistant Professor Fae Azhari is helping stretch those dollars farther by keeping our buildings, bridges, roads and reservoirs safe and structurally sound for longer.

Azhari’s research focuses on structural health monitoring. Just as you visit the doctor for periodic check-ups, structures need their health checked too – but instead of blood tests and heart rate measurements, engineers usually perform visual inspections and spot-checks with sensors and instruments.

“The problem with visual inspections is that they’re pretty subjective, and with periodic monitoring, you can miss certain events or failures,” says Azhari. “Now we’re moving toward continuous monitoring by incorporating permanent sensors on important structures to get real-time data.”

Degradation or damage suffered between inspections can have catastrophic consequences. In June 2013, a rail bridge just outside of downtown Calgary partially collapsed as a train was passing over it. The train, carrying flammable and toxic liquids, derailed. Emergency measures were taken to prevent the railcars from falling into the Bow River, which was running high with summer floodwater. The Transportation Safety Board of Canada determined that floodwaters had eroded the soil around the bridge’s foundations, causing the collapse. This loss of sediment from around foundational supports is called scour.

“Believe it or not, this happens very often, especially in North America and some Asian countries,” says Azhari. “Scour is a huge problem.”

For her PhD research at the University of California, Davis, Azhari tackled scour from a new angle: she took commercially available sensors that measure dissolved oxygen, typically used for agriculture or biological applications, and used them for sensing scour.

Azhari’s design was to attach a number of oxygen sensors at increasing depths along the buried length of the bridge pier. If the pier is properly buried, the dissolved oxygen levels detected by the sensors should be very low – but as scour erodes the sediments and exposes the sensors to flowing water, the dissolved oxygen levels rise. As scour progresses, more and more sensors become exposed, indicating how badly scour is threatening the bridge’s structural integrity.

She has also worked on concrete sensors, including a design that integrates conductive carbon fibers and nanotubes into concrete, making it a self-sensing material. Measuring the resistance across the material reveals the stresses and strains on it.

“This technology is well-proven in the laboratory, but moving it to the field is a big challenge,” says Azhari.

As she builds her research enterprise, Azhari plans to collaborate across disciplines and with key partners who could benefit from her sensors, as well her analysis and insight into the data that comes from them.

“Transportation infrastructure, utilities, dams, power plants, wind turbines – basically any engineering system – needs maintenance and monitoring,” she says.

“It’s very important to get these sensors from prototype to implementation, and I want to work on that.”