OCS Student Intern Nina Sing (N) interviewed Dr. Kimberly Kurtis (K) about innovations in smart city infrastructure.
The size of populations residing in cities has continued to grow since the 1950’s calling for a new way to organize and maintain its growth. The ‘smart cities’ initiative incorporates elements aimed to improve resiliency, environmental stability, and quality of life. An interesting component of this initiative is Dr. Kimberly Kurtis’s research on alternative cements. Dr. Kurtis shares with me how her research plays an innovative part in creating the new wave of cities’ infrastructures.
N: Can you tell me about your background as a researcher and what prompted your focus on sustainable research?
K: I think it’s just been a natural evolution, with respect to cement and concrete, the area which I work in. You could argue that for a long time there was a real emphasis on strength, and that was the primary property that people were interested in that material. From there research evolved and people started looking at performance criteria beyond strength or other mechanical properties. Looking at things like permeability and durability of the material, how it can last longer. And so then the natural evolution to that is to make structures last longer, extending the life span and reducing the need to reconstruct, reducing the need for maintenance and repair, and start looking at the planning of the project. How do we choose the right material for the application, how do we compose and process that material so that its environmental impact is as minimal as possible?
N: What was your inspiration behind this research?
K: Most people recognize that concrete is a ubiquitous material, you encounter it every day. But they may not realize that it is the most widely used material on the planet after water. We build so many things out of concrete, tall buildings, dams, bridges, sidewalks, your home, your driveway. As a result, there is a tremendous opportunity to contribute to sustainability even by reducing the environmental impact by a small fraction.
N: The description of your research states that alternative cement chemistries such as calcium sulfoaluminates and magnesium phosphates can cut CO2 emissions by one-half. How does that process work?
K: Part of the embodied CO2 gas emissions are associated with the calcination process. Traditional cements are based on calcium silicate chemistry and calcium aluminate chemistry. In the process we heat up a lot of calcium carbonate, limestone, and decompose that to calcium oxide. So as a result you emit CO2. So some of the greenhouse gas emissions come from that process, another portion comes from the heat that’s needed in order the get the calcination to happen. For traditional cement manufacturers that can be as hot as 1450°C there are a lot of fossil fuels needed in order to make the flux to make those reactions occur in a kiln. With alternative more sustainable cements there are two ways to save in greenhouse gases. One you can reduce the amount of CO2 that’s evolved from the calcination of limestone simply by shifting the chemistry. We can look at cements that have a lower calcium oxide content, then they will have a lower CO2 emission during the manufacturing process just by the calcination process itself. In addition, some of these cements can be calcined at lower temperatures, so there’s a fuels savings as well.
N: How are you able to reduce the content required for the cement while increasing its durability?
K: Some of these alternative cements have higher strengths, and so the 50% savings in greenhouse gas emissions assumes we are using it as a 1:1 replacement. If I was using a ton of cement to create a column that calculation assumes I need a ton of this alternative cement, but it may be that the alternative cement has twice the strength of the traditional cement so we could reduce the cross section of the column because it will have more load bearing capacity. So you could achieve even greater savings through increased strength.
N: Is it through the different compositions that there’s increased strength?
K: Not all compositions will have increased strength. Strength is no longer the only quality we are designing for anymore. Some will have reduced permeability and some will have greater resistance to extreme environments like high temperature that can make them suited for specific applications. And that’s really what we’re working towards, figuring out which alternative cements are best for which applications and which environments.
N: You mentioned that each type of binder has its own pros and cons. Can you give me an example of each in a certain scenario?
K: Two examples come to mind. One is magnesium phosphate cements; they have extreme resistance to high temperature so there’s a plethora of useful applications for those materials. They can be used in manufacturing processes, they have airfield applications, but they also have challenges in setting time, they can set very rapidly so it may not be the best material for constructing in a remote location where you have to transport the material. Another example would be calcium aluminate cements. They have very good sulfate attack resistance and good corrosion resistance but they are also susceptible to a process called conversion where they lose some of their strength over time, so you need to account for that when you design with calcium aluminates and design with the converted strength rather than the initial strength.
N: What issues have you faced while developing this research?
K: Right now one of our biggest challenges is adapting existing test methods so these materials can be rapidly assessed and their results quantified in a way they can be included in specifications. Civil infrastructure is largely designed according to code, so if these materials are not in the code it makes it very challenging to be able to use them in practice especially in large scale infrastructure applications. So the first step in getting them into the codes and infrastructure are consistent and standardized ways to assess their properties so they can be compared to one another. And current specifications, current test methods don’t do a good job of addressing a range of materials, they’re really focused on traditional materials.
N: How soon do you see the implementation of alternative cement and on a broader scale the smart city.
K: From my perspective, we were surprised in the beginning how open different state departments of transportation were in considering smart cements. Maybe about half of the states already have experience with these. So I think it’s here, and it’s only going to be growing and I think our real challenge is going to be going to facilitate the more rapid upscaling of their use. I think on a broader scale materials are an important part of the smart city’s concept. They physically embody the infrastructure that we are delivering to society, and so I think the choice in materials plays an essential role in the smart city. And we can go way beyond alternative cement and think about smart or adaptable materials, self-healing materials, lots of different opportunities exist there and I think green cement is one small part of the role materials play in developing smart cities, but an important one.
N: Why do you believe sustainable research as a whole is relevant today?
K: Ahh that’s a challenging question in this political climate. Everyone recognizes there are resource constraints, it could be time, money, and in this case we think about environmental impact, and economy. So if we extend service we life we contribute not only to sustainability but we also reduce the economic cost of infrastructure by reducing the needs for maintenance and repair, rehabilitation, and reconstruction. Thinking about material selection in a comprehensive and holistic way at the beginning of a project is very helpful in terms of delivering resilient infrastructure to society.