20 June, 2022
From the rise of Brutalist architecture, to Federal infrastructure plans, to concrete jungles where dreams are made of, it’s hard to escape from concrete’s presence. In fact, concrete is the second widest used material in the world behind only water. Once a symbol for urban renewal, concrete is used in roads, sidewalks, urban landscaping, and structures of all size. It is praised for its high strength, durability, and versatility in how it is made and implemented.
What is lesser known about concrete is its massive carbon footprint. One ton of concrete produced equates to one ton of carbon emissions, and its production accounts for 8-10% of the world’s carbon emissions. With increasing awareness of climate change, engineers are finding ways to create greener solutions while benefitting from the perks of concrete.
One solution engineers are exploring is recycled concrete, also known as green concrete (no, this does not mean mint-colored highways are in our future). Concrete’s venerable recipe is simple: Portland cement, aggregates (commonly sand and gravel), water, and optional binders that can increase strength depending on the application. Green concrete uses recycled ingredients for at least one of these components.
Replacing traditional aggregate with waste material is one of the most widely studied practices. Recycled materials could include excavated concrete and asphalt, glass, and plastic. Using binders can reduce the amount of cement needed for a given strength (thus reducing embodied carbon), and using recycled materials makes it even better. Some common recycled binders include agricultural waste like wood ash, industrial waste like fly ash, and mineral waste like limestone. Not only does this practice reduce the carbon emissions needed for production, but it also diverts waste from the landfill.
There is a common misconception that green building design is more expensive than traditional methods. While a rooftop rain collecting and purifying plant may have a hefty price tag, green building techniques can actually be more cost effective than conventional methods.
For example, if a building has a wall with a high R-value (a measurement of how insulated it is), there will be a reduction in unwanted heat loss or gain. Because of this, the energy demand will be lower, and so will be the electric bill. While this may be more of an upfront cost on the building envelope alone, the building will require smaller HVAC systems and save money on that front.
Not only can green building techniques save money on the building cost, but it is also beneficial for the client in numerous ways. The United States Green Building Council (USGBC) awards LEED Certifications based on green building practices, and recipients can display their certification. This can improve the client’s public image, which could lead into an increase in revenue, perspective employee interest, and company culture.
Not only can green building techniques save money on the building cost, but it is also beneficial for the client in numerous ways
In addition to helping the planet, green building techniques are better for the people. Numerous case studies have shown that people who work in eco-friendly buildings report better health, a reduction in absenteeism, and increased happiness and wellbeing.
Because of these benefits, many companies and builders are enthused from an economic perspective: building cost reduction, attracting clientele, and worker productivity return. Recycled concrete has the potential to take center stage in these initiatives.
While green concrete may seem like the perfect alternative to its conventional counterpart, developers often turn a blind eye to the environmental impact of their projects. In an industry where buildings are erecting faster than the pace of discovery, developers favor economic gain over ecofriendly building techniques. Lacking knowledge of the cost savings green building techniques can provide, they often opt for the status quo of traditional building methods and materials.
Part of the assumption that green building techniques are always more expensive is justified. Smart facades or windows that change automatically depending on the weather and lighting are far more expensive than a simple piece of glass. In the case of concrete, it’s ancient recipe is relatively inexpensive, and newly established recycled concrete could come at a heightened cost.
There are countless researchers studying its potential. While some have shown results with a lower carbon footprint and adequate strength, others have not been as successful. Because of this, it is a high-risk, low-reward product. In addition, green concrete is a relatively new phenomenon, so its long-term behavior in unknown; it is possible that it could need numerous repairs down the line, undoing the carbon savings it was created for. Researchers may be hesitant about spending their time and resources testing a potentially unsuccessful product, and even eco-minded developers would not want to invest in a risky product.
For recycled concrete to be widely implemented in the construction industry, it needs to be attractive to all stakeholders. The first of which are engineers making the product. There are countless studies with varying results; some are successful while others do not meet the mark. Sharing findings and resources could help contribute to more successful findings.
For recycled concrete to be widely implemented in the construction industry, it needs to be attractive to all stakeholders.
The second stakeholder involved are builders and developers who purchase the concrete. There is currently very little demand for recycled concrete, so the first step would be to change this. As mentioned previously, the USGBC LEED Certification is becoming a motivator for developers to encourage clients to use green building techniques. At the moment, recycled building materials is not a part of the certification classification. Adding it to the score card could further incentivize. In addition, it would spread awareness and knowledge about its benefits.
Another way to increase demand is to make recycled concrete more economically rewarding. Many developers face a decision of economic gain or environmental savings, and more often than not, they go with the former. Increasing economic attractiveness could include creating tax incentives for its use, taxing conventional concrete or embodied carbon, or funding research for long-term use.
The final stakeholder in recycled concrete is you, the inhabitants. Concrete has numerous benefits like serving as a thermal mass to reduce the heating/cooling demand, high strength to increase the amount of window exposure, and durability to increase the longevity and reduce the number of needed repairs. Furthermore, recycled concrete contributes to an even greater environmental impact. Green building techniques can improve working conditions by bettering air quality, increasing window exposure, improving company culture and image, lowering pollution, and reducing stress to improve quality of life. Increasing the knowledge of what green buildings can offer will increase demand for green concrete.
At the end of the day, drastic changes to our current way of life need to be made to save the planet from irreversible damage. Building production and use account for nearly 36% of global carbon emissions. Since concrete is responsible for much of this, it is vital that engineers develop ways to cut back on its embodied carbon. Green concrete has the potential to make a positive environmental impact and improve our way of life for the planet at large.
Sources:
Souto-Martinez, A, and W V Srubar III. Embodied Carbon of Buildings, edited by A B Liel, Springer International Publishing AG, 2018, pp. 77–98.
Kumar Pancharathi, Rathish, et al., editors. Advances in Sustainable Construction Materials. Springer Nature Singapore Pte Ltd., 2020.
Behera, Monalisa, et al. “Recycled Aggregate from C&D Waste & Its Use in Concrete.” Construction and Building Materials, vol. 68, 26 July 2014, pp. 501–516.
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Jahanbakhsh, Hamid, et al. “Sustainable Asphalt Concrete Containing High Reclaimed Asphalt Pavements and Recycling Agents: Performance Assessment, Cost Analysis, and Environmental Impact.” Journal of Cleaner Production, vol. 224, 13 Oct. 2019.
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