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    Enabling a circular economy in the built environment

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    The amount of waste generated by the construction sector underscores an urgent need for embracing circularity — a sustainable model that aims to minimize waste and maximize material efficiency through recovery and reuse — in the built environment: 600 million tons of construction and demolition waste was produced in the United States alone in 2018, with 820 million tons reported in the European Union, and an excess of 2 billion tons annually in China.This significant resource loss embedded in our current industrial ecosystem marks a linear economy that operates on a “take-make-dispose” model of construction; in contrast, the “make-use-reuse” approach of a circular economy offers an important opportunity to reduce environmental impacts.A team of MIT researchers has begun to assess what may be needed to spur widespread circular transition within the built environment in a new open-access study that aims to understand stakeholders’ current perceptions of circularity and quantify their willingness to pay.“This paper acts as an initial endeavor into understanding what the industry may be motivated by, and how integration of stakeholder motivations could lead to greater adoption,” says lead author Juliana Berglund-Brown, PhD student in the Department of Architecture at MIT.Considering stakeholders’ perceptionsThree different stakeholder groups from North America, Europe, and Asia — material suppliers, design and construction teams, and real estate developers — were surveyed by the research team that also comprises Akrisht Pandey ’23; Fabio Duarte, associate director of the MIT Senseable City Lab; Raquel Ganitsky, fellow in the Sustainable Real Estate Development Action Program; Randolph Kirchain, co-director of MIT Concrete Sustainability Hub; and Siqi Zheng, the STL Champion Professor of Urban and Real Estate Sustainability at Department of Urban Studies and Planning.Despite growing awareness of reuse practice among construction industry stakeholders, circular practices have yet to be implemented at scale — attributable to many factors that influence the intersection of construction needs with government regulations and the economic interests of real estate developers.The study notes that perceived barriers to circular adoption differ based on industry role, with lack of both client interest and standardized structural assessment methods identified as the primary concern of design and construction teams, while the largest deterrents for material suppliers are logistics complexity, and supply uncertainty. Real estate developers, on the other hand, are chiefly concerned with higher costs and structural assessment. Yet encouragingly, respondents expressed willingness to absorb higher costs, with developers indicating readiness to pay an average of 9.6 percent higher construction costs for a minimum 52.9 percent reduction in embodied carbon — and all stakeholders highly favor the potential of incentives like tax exemptions to aid with cost premiums.Next steps to encourage circularityThe findings highlight the need for further conversation between design teams and developers, as well as for additional exploration into potential solutions to practical challenges. “The thing about circularity is that there is opportunity for a lot of value creation, and subsequently profit,” says Berglund-Brown. “If people are motivated by cost, let’s provide a cost incentive, or establish strategies that have one.”When it comes to motivating reasons to adopt circularity practices, the study also found trends emerging by industry role. Future net-zero goals influence developers as well as design and construction teams, with government regulation the third-most frequently named reason across all respondent types.“The construction industry needs a market driver to embrace circularity,” says Berglund-Brown, “Be it carrots or sticks, stakeholders require incentives for adoption.”The effect of policy to motivate change cannot be understated, with major strides being made in low operational carbon building design after policy restricting emissions was introduced, such as Local Law 97 in New York City and the Building Emissions Reduction and Disclosure Ordinance in Boston. These pieces of policy, and their results, can serve as models for embodied carbon reduction policy elsewhere.Berglund-Brown suggests that municipalities might initiate ordinances requiring buildings to be deconstructed, which would allow components to be reused, curbing demolition methods that result in waste rather than salvage. Top-down ordinances could be one way to trigger a supply chain shift toward reprocessing building materials that are typically deemed “end-of-life.”The study also identifies other challenges to the implementation of circularity at scale, including risk associated with how to reuse materials in new buildings, and disrupting status quo design practices.“Understanding the best way to motivate transition despite uncertainty is where our work comes in,” says Berglund-Brown. “Beyond that, researchers can continue to do a lot to alleviate risk — like developing standards for reuse.”Innovations that challenge the status quoDisrupting the status quo is not unusual for MIT researchers; other visionary work in construction circularity pioneered at MIT includes “a smart kit of parts” called Pixelframe. This system for modular concrete reuse allows building elements to be disassembled and rebuilt several times, aiding deconstruction and reuse while maintaining material efficiency and versatility.Developed by MIT Climate and Sustainability Consortium Associate Director Caitlin Mueller’s research team, Pixelframe is designed to accommodate a wide range of applications from housing to warehouses, with each piece of interlocking precast concrete modules, called Pixels, assigned a material passport to enable tracking through its many life cycles.Mueller’s work demonstrates that circularity can work technically and logistically at the scale of the built environment — by designing specifically for disassembly, configuration, versatility, and upfront carbon and cost efficiency.“This can be built today. This is building code-compliant today,” said Mueller of Pixelframe in a keynote speech at the recent MCSC Annual Symposium, which saw industry representatives and members of the MIT community coming together to discuss scalable solutions to climate and sustainability problems. “We currently have the potential for high-impact carbon reduction as a compelling alternative to the business-as-usual construction methods we are used to.”Pixelframe was recently awarded a grant by the Massachusetts Clean Energy Center (MassCEC) to pursue commercialization, an important next step toward integrating innovations like this into a circular economy in practice. “It’s MassCEC’s job to make sure that these climate leaders have the resources they need to turn their technologies into successful businesses that make a difference around the world,” said MassCEC CEO Emily Reichart, in a press release.Additional support for circular innovation has emerged thanks to a historic piece of climate legislation from the Biden administration. The Environmental Protection Agency recently awarded a federal grant on the topic of advancing steel reuse to Berglund-Brown — whose PhD thesis focuses on scaling the reuse of structural heavy-section steel — and John Ochsendorf, the Class of 1942 Professor of Civil and Environmental Engineering and Architecture at MIT.“There is a lot of exciting upcoming work on this topic,” says Berglund-Brown. “To any practitioners reading this who are interested in getting involved — please reach out.”The study is supported in part by the MIT Climate and Sustainability Consortium. 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      Think globally, rebuild locally

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      Building construction accounts for a huge chunk of greenhouse gas emissions: About 36 percent of carbon dioxide emissions and 40 percent of energy consumption in Europe, for instance. That’s why the European Union has developed regulations about the reuse of building materials.

      Some cities are adding more material reuse into construction already. Amsterdam, for example, is attempting to slash its raw material use by half by 2030. The Netherlands as a whole aims for a “circular economy” of completely reused materials by 2050.

      But the best way to organize the reuse of construction waste is still being determined. For one thing: Where should reusable building materials be stored before they are reused? A newly published study focusing on Amsterdam finds the optimal material reuse system for construction has many local storage “hubs” that keep materials within a few miles of where they will be needed.

      “Our findings provide a starting point for policymakers in Amsterdam to strategize land use effectively,” says Tanya Tsui, a postdoc at MIT and a co-author of the new paper. “By identifying key locations repeatedly favored across various hub scenarios, we underscore the importance of prioritizing these areas for future circular economy endeavors in Amsterdam.”

      The study adds to an emerging research area that connects climate change and urban planning.

      “The issue is where you put material in between demolition and new construction,” says Fábio Duarte, a principal researcher at MIT’s Senseable City Lab and a co-author of the new paper. “It will have huge impacts in terms of transportation. So you have to define the best sites. Should there be only one? Should we hold materials across a wide number of sites? Or is there an optimal number, even if it changes over time? This is what we examined in the paper.”

      The paper, “Spatial optimization of circular timber hubs,” is published in NPJ Nature Urban Sustainability. The authors are Tsui, who is a postdoc at the MIT Senseable Amsterdam Lab in the Amsterdam Institute for Advanced Metropolitan Solutions (AMS); Titus Venverloo, a research fellow at MIT Senseable Amsterdam Lab and AMS; Tom Benson, a researcher at the Senseable City Lab; and Duarte, who is also a lecturer in MIT’s Department of Urban Studies and Planning and the MIT Center for Real Estate.

      Numerous experts have previously studied at what scale the “circular economy” of reused materials might best operate. Some have suggested that very local circuits of materials recycling make the most sense; others have proposed that building-materials recycling will work best at a regional scale, with a radius of distribution covering 30 or more miles. Some analyses contend that global-scale reuse will be necessary to an extent.

      The current study adds to this examination of the best geographic scale for using construction materials again. Currently the storage hubs that do exist for such reused materials are chosen by individual companies, but those locations might not be optimal either economically or environmentally. 

      To conduct the study, the researchers essentially conducted a series of simulations of the Amsterdam metropolitan area, focused exclusively on timber reuse. The simulations examined how the system would work if anywhere from one to 135 timber storage hubs existed in greater Amsterdam. The modeling accounted for numerous variables, such as emissions reductions, logistical factors, and even how changing supply-and-demand scenarios would affect the viability of the reusehubs.

      Ultimately, the research found that Amsterdam’s optimal system would have 29 timber hubs, each serving a radius of about 2 miles. That setup generated 95 percent of the maximum reduction in CO2 emissions, while retaining logistical and economic benefits.

      That results also lands firmly on the side of having more localized networks for keeping construction materials in use.

      “If we have demolition happening in certain sites, then we can project where the best spots around the city are to have these circular economy hubs, as we call them,” Duarte says. “It’s not only one big hub — or one hub per construction site.”

      The study seeks to identify not only the optimal number of storage sites, but to identify where those sites might be.

      “[We hope] our research sparks discussions regarding the location and scale of circular hubs,” Tsui says. “While much attention has been given to governance aspects of the circular economy in cities, our study demonstrates the potential of utilizing location data on materials to inform decisions in urban planning.”

      The simulations also illuminated the dynamics of materials reuse. In scenarios where Amsterdam had from two to 20 timber recycling hubs, the costs involved lowered as the number of hubs increased — because having more hubs reduces transportation costs. But when the number of hubs went about 40, the system as a whole became more expensive — because each timber depot was not storing enough material to justify the land use.

      As such, the results may be of interest to climate policymakers, urban planners, and business interests getting involved in implementing the circular economy in the construction industry.

      “Ultimately,” Tsui says, “we envision our research catalyzing meaningful discussions and guiding policymakers toward more informed decisions in advancing the circular economy agenda in urban contexts.”

      The research was supported, in part, by the European Union’s Horizon 2020 research and innovation program. More

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      Technologies for water conservation and treatment move closer to commercialization

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      The Abdul Latif Jameel Water and Food Systems Lab (J-WAFS) provides Solutions Grants to help MIT researchers launch startup companies or products to commercialize breakthrough technologies in water and food systems. The Solutions Grant Program began in 2015 and is supported by Community Jameel. In addition to one-year, renewable grants of up to $150,000, the program also matches grantees with industry mentors and facilitates introductions to potential investors. Since its inception, the J-WAFS Solutions Program has awarded over $3 million in funding to the MIT community. Numerous startups and products, including a portable desalination device and a company commercializing a novel food safety sensor, have spun out of this support.

      The 2023 J-WAFS Solutions Grantees are Professor C. Cem Tasan of the Department of Materials Science and Engineering and Professor Andrew Whittle of the Department of Civil and Environmental Engineering. Tasan’s project involves reducing water use in steel manufacturing and Whittle’s project tackles harmful algal blooms in water. Project work commences this September.

      “This year’s Solutions Grants are being award to professors Tasan and Whittle to help commercialize technologies they have been developing at MIT,” says J-WAFS executive director Renee J. Robins. “With J-WAFS’ support, we hope to see the teams move their technologies from the lab to the market, so they can have a beneficial impact on water use and water quality challenges,” Robins adds.

      Reducing water consumption by solid-state steelmaking

      Water is a major requirement for steel production. The steel industry ranks fourth in industrial freshwater consumption worldwide, since large amounts of water are needed mainly for cooling purposes in the process. Unfortunately, a strong correlation has also been shown to exist between freshwater use in steelmaking and water contamination. As the global demand for steel increases and freshwater availability decreases due to climate change, improved methods for more sustainable steel production are needed.

      A strategy to reduce the water footprint of steelmaking is to explore steel recycling processes that avoid liquid metal processing. With this motivation, Cem Tasan, the Thomas B. King Associate Professor of Metallurgy in the Department of Materials Science and Engineering, and postdoc Onur Guvenc PhD created a new process called Scrap Metal Consolidation (SMC). SMC is based on a well-established metal forming process known as roll bonding. Conventionally, roll bonding requires intensive prior surface treatment of the raw material, specific atmospheric conditions, and high deformation levels. Tasan and Guvenc’s research revealed that SMC can overcome these restrictions by enabling the solid-state bonding of scrap into a sheet metal form, even when the surface quality, atmospheric conditions, and deformation levels are suboptimal. Through lab-scale proof-of-principle investigations, they have already identified SMC process conditions and validated the mechanical formability of resulting steel sheets, focusing on mild steel, the most common sheet metal scrap.

      The J-WAFS Solutions Grant will help the team to build customer product prototypes, design the processing unit, and develop a scale-up strategy and business model. By simultaneously decreasing water usage, energy demand, contamination risk, and carbon dioxide burden, SMC has the potential to decrease the energy need for steel recycling by up to 86 percent, as well as reduce the linked carbon dioxide emissions and safeguard the freshwater resources that would otherwise be directed to industrial consumption. 

      Detecting harmful algal blooms in water before it’s too late

      Harmful algal blooms (HABs) are a growing problem in both freshwater and saltwater environments worldwide, causing an estimated $13 billion in annual damage to drinking water, water for recreational use, commercial fishing areas, and desalination activities. HABs pose a threat to both human health and aquaculture, thereby threatening the food supply. Toxins in HABs are produced by some cyanobacteria, or blue-green algae, whose communities change in composition in response to eutrophication from agricultural runoff, sewer overflows, or other events. Mitigation of risks from HABs are most effective when there is advance warning of these changes in algal communities. 

      Most in situ measurements of algae are based on fluorescence spectroscopy that is conducted with LED-induced fluorescence (LEDIF) devices, or probes that induce fluorescence of specific algal pigments using LED light sources. While LEDIFs provide reasonable estimates of concentrations of individual pigments, they lack resolution to discriminate algal classes within complex mixtures found in natural water bodies. In prior research, Andrew Whittle, the Edmund K. Turner Professor of Civil and Environmental Engineering, worked with colleagues to design REMORA, a low-cost, field-deployable prototype spectrofluorometer for measuring induced fluorescence. This research was part of a collaboration between MIT and the AMS Institute. Whittle and the team successfully trained a machine learning model to discriminate and quantify cell concentrations for mixtures of different algal groups in water samples through an extensive laboratory calibration program using various algae cultures. The group demonstrated these capabilities in a series of field measurements at locations in Boston and Amsterdam. 

      Whittle will work with Fábio Duarte of the Department of Urban Studies and Planning, the Senseable City Lab, and MIT’s Center for Real Estate to refine the design of REMORA. They will develop software for autonomous operation of the sensor that can be deployed remotely on mobile vessels or platforms to enable high-resolution spatiotemporal monitoring for harmful algae. Sensor commercialization will hopefully be able to exploit the unique capabilities of REMORA for long-term monitoring applications by water utilities, environmental regulatory agencies, and water-intensive industries.  More

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      Low-cost device can measure air pollution anywhere

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      Air pollution is a major public health problem: The World Health Organization has estimated that it leads to over 4 million premature deaths worldwide annually. Still, it is not always extensively measured. But now an MIT research team is rolling out an open-source version of a low-cost, mobile pollution detector that could enable people to track air quality more widely.

      The detector, called Flatburn, can be made by 3D printing or by ordering inexpensive parts. The researchers have now tested and calibrated it in relation to existing state-of-the-art machines, and are publicly releasing all the information about it — how to build it, use it, and interpret the data.

      “The goal is for community groups or individual citizens anywhere to be able to measure local air pollution, identify its sources, and, ideally, create feedback loops with officials and stakeholders to create cleaner conditions,” says Carlo Ratti, director of MIT’s Senseable City Lab. 

      “We’ve been doing several pilots around the world, and we have refined a set of prototypes, with hardware, software, and protocols, to make sure the data we collect are robust from an environmental science point of view,” says Simone Mora, a research scientist at Senseable City Lab and co-author of a newly published paper detailing the scanner’s testing process. The Flatburn device is part of a larger project, known as City Scanner, using mobile devices to better understand urban life.

      “Hopefully with the release of the open-source Flatburn we can get grassroots groups, as well as communities in less developed countries, to follow our approach and build and share knowledge,” says An Wang, a researcher at Senseable City Lab and another of the paper’s co-authors.

      The paper, “Leveraging Machine Learning Algorithms to Advance Low-Cost Air Sensor Calibration in Stationary and Mobile Settings,” appears in the journal Atmospheric Environment.

      In addition to Wang, Mora, and Ratti the study’s authors are: Yuki Machida, a former research fellow at Senseable City Lab; Priyanka deSouza, an assistant professor of urban and regional planning at the University of Colorado at Denver; Tiffany Duhl, a researcher with the Massachusetts Department of Environmental Protection and a Tufts University research associate at the time of the project; Neelakshi Hudda, a research assistant professor at Tufts University; John L. Durant, a professor of civil and environmental engineering at Tufts University; and Fabio Duarte, principal research scientist at Senseable City Lab.

      The Flatburn concept at Senseable City Lab dates back to about 2017, when MIT researchers began prototyping a mobile pollution detector, originally to be deployed on garbage trucks in Cambridge, Massachusetts. The detectors are battery-powered and rechargable, either from power sources or a solar panel, with data stored on a card in the device that can be accessed remotely.

      The current extension of that project involved testing the devices in New York City and the Boston area, by seeing how they performed in comparison to already-working pollution detection systems. In New York, the researchers used 5 detectors to collect 1.6 million data points over four weeks in 2021, working with state officials to compare the results. In Boston, the team used mobile sensors, evaluating the Flatburn devices against a state-of-the-art system deployed by Tufts University along with a state agency.

      In both cases, the detectors were set up to measure concentrations of fine particulate matter as well as nitrogen dioxide, over an area of about 10 meters. Fine particular matter refers to tiny particles often associated with burning matter, from power plants, internal combustion engines in autos and fires, and more.

      The research team found that the mobile detectors estimated somewhat lower concentrations of fine particulate matter than the devices already in use, but with a strong enough correlation so that, with adjustments for weather conditions and other factors, the Flatburn devices can produce reliable results.

      “After following their deployment for a few months we can confidently say our low-cost monitors should behave the same way [as standard detectors],” Wang says. “We have a big vision, but we still have to make sure the data we collect is valid and can be used for regulatory and policy purposes,”

      Duarte adds: “If you follow these procedures with low-cost sensors you can still acquire good enough data to go back to [environmental] agencies with it, and say, ‘Let’s talk.’”

      The researchers did find that using the units in a mobile setting — on top of automobiles — means they will currently have an operating life of six months. They also identified a series of potential issues that people will have to deal with when using the Flatburn detectors generally. These include what the research team calls “drift,” the gradual changing of the detector’s readings over time, as well as “aging,” the more fundamental deterioration in a unit’s physical condition.

      Still, the researchers believe the units will function well, and they are providing complete instructions in their release of Flatburn as an open-source tool. That even includes guidance for working with officials, communities, and stakeholders to process the results and attempt to shape action.

      “It’s very important to engage with communities, to allow them to reflect on sources of pollution,” says Mora. 

      “The original idea of the project was to democratize environmental data, and that’s still the goal,” Duarte adds. “We want people to have the skills to analyze the data and engage with communities and officials.” More