Future Forward Interview: Materials Help Move Beyond Rehabilitation to Ongoing Sustainability
Ongoing research into micro- and nano-modified materials holds promise to improve material lifespan as well as rehabilitate compromised structures. Informed Infrastructure’s Editorial Director Matt Ball spoke to Nemkumar (Nemy) Banthia, PhD, PEng, a distinguished university scholar at the University of British Columbia, about his application of materials science to structural engineering as well as his work on overall sustainability in his role as scientific director of the India-Canada Centre for Innovative Multidisciplinary Partnerships to Accelerate Community Transformation and Sustainability (IC-IMPACTS).
[Banthia also is the focus of the “Future Forward” page in the inaugural January/February 2015 issue of Informed Infrastructure.]
I2: What has been the focus of your research?
Banthia: My focus has always been innovative construction materials, and expanding their use in concrete structures. I specialize on the material side, but my background is in structural engineering. I’m kind of a bridge to take the materials and apply them into structures.
We have these two isolated groups, where the materials people don’t worry about the structure that much. They get into the nano and the micro optimization, and they then give the material over to the structural engineers to use. I work on materials, and my training is in structural engineering, so I’m able to take innovation in materials and apply it into structural engineering.
As a structural engineer, I don’t treat materials as a “black box,” and as a materials engineer, I don’t treat structures as a “black box.”
I2: In terms of the fiber materials that you’ve developed, what are some of the factors in their application to ensure they perform well?
Banthia: In the case of repair, you’re looking for bond, so that the new material on an old structure has an optimized interface. The repair material also becomes the first line of resistance against the environmental conditions, so you need much better durability of the material.
In essence you are not developing repair materials but repair systems that not only bring the structure back to its old capacity, but we also need to make sure that the solution is sustainable and will last longer and perform as we expected it to perform.
I2: What is your definition of sustainability as it relates to infrastructure?
Banthia: Sustainability to me means using building materials that have a low carbon footprint. Materials that have come from different industrial sources and absorb waste products that would have ended up in a landfill are a start. Finally, sustainability means building really durable structures. Nothing is sustainable if the structures last just 50 years. If you’re demolishing and building new structures, the resource requirements are far greater than building the right way with durable systems so that the building lasts much longer.
I2: What is your big-picture view on where we can improve civil and structural engineering practice?
Banthia: Taking the whole spectrum, our biggest problem in civil engineering, and really every field, is that we are too fragmented. We stay in our little cocoons and don’t see the full length of application. If you look at structures today—a bridge, for example—we design it for 100 years, and the average lifespan is a dismal 37 years.
While we pretend that we understand how the bridge performs or how materials interact with loads or how structures interact with materials, we don’t do a good job of it. This means that our bridges last much shorter than what we pretend we are designing them for. That’s an indictment of a civil engineer, I think. If you know it so well, and if you’re doing a good job of optimizing materials and creating advanced designs, we should be able to at least design what we think we are designing.
The problem is that we are completely isolated—we don’t have a holistic approach. We need a full synergy among different disciplines. If you were able to do that, then I think these problems would go away.
I2: Your focus—and even the name of your lab with “rehabilitation and sustainability” in the title—is to extend lifespans, and you’ve done that through innovation in materials. It also sounds like you’re focused on how we can do a better job in our designs for better long-term performance.
Banthia: Part of the reason why bridges or structures don’t last very long is because we don’t maintain them very well. Maintenance means doing a proper condition assessment, and if we understand that the bridge does not have the load capacity that’s required, then we need to repair it and rehabilitate it. That’s not happening, unfortunately.
The problem is that we don’t have good condition-assessment tools. If you recall, the overpass that collapsed in Montreal in 2006 was inspected that same week that it collapsed. What it tells you immediately is that our condition-assessment tools are very poor. We have no idea what condition some of these old structure are in.
If you had a clear view of condition, then you would design and devise much better rehabilitation solutions. You would maintain these structures properly. But we do neither.
I don’t want to be too negative, but there is a lot of synergy needed among disciplines. At the very least, we must have better tools for condition assessment, which is what my research chair is working on right now.
I2: Are you involved in the ongoing sensing and monitoring of structures?
Banthia: Yes, that’s part of the condition assessment. The assessment could either be a periodic one, where you can do a scan with short-pulse radar, ultrasonics, CT-scans, radiography, radiometry, magnetic resonance imaging, stress-pulse methods or active thermographs. You can do a lot of things to a bridge, hooking up these different instruments. The other thing you can do is to put embedded sensors—such as fiber-optics or piezoresistives– in the structures, which can give you real-time readings. With continual data, you get a sense of how it is performing overall. It is important to do both.
We are working on these assessment technologies as well as developing sensors from carbon nanotubes. These are very tiny sensors that you can place on the structure and hook up on a transmission device to tell you wire-lessly over the Internet what’s happening with a structure over time. You have both periodic and continual assessments with this approach.
I2: With carbon nanotubes embedded in the concrete, is the material then becoming the sensor?
Banthia: Yes, but I would not go so far as to construct the entire bridge with carbon nanotubes, that would be too expensive. I would install small sensors that are also made of concrete throughout the structure, with hundreds of sensors in strategic places. These sensors would have nanotubes, and hooked up to a power and transmission source would give a complete picture of what the bridge is undergoing at any point in time. I could reconstruct what the bridge is doing from these sensor readings.
For example, during an earthquake, these sensors would transmit data so that at the end of the shaking, I would be able to tell if that bridge should be used, repaired or condemned.
There are a lot of questions that are asked right after an earthquake: whether a bridge should be closed or repaired. This kind of data would allow us to make that decision. We would be able to see how the bridge performed and calculate the residual capacity.
I2: Does this get us to the point where we understand performance in a whole new light?
Banthia: Absolutely. What we’re also doing with sensors is giving you design rationale. There are a lot of knowns in our designs factors: you multiply the live load by a factor or the dead load by a factor. The factors account for uncertainty, because we don’t really know. If you had the data, then you would design better for uncertainty and reduce the multiplication factors further to design what is needed. That’s sustainability.
We are wasting a lot of material in our structures now due to uncertainty. The moment you have real data from a real structure, you can truly understand what kind of live loads we see in a specific region, on a specific road, at a specific time of year, etc., for the next one you design. This would help us to tighten our design and see how the structures perform.
On the materials side, we have a lot of variability in there. We have all of these wonderful safety factors that make some of these structures “over-safe.” We’re just wasting materials, and its unsustainable. The sensors will tell you how materials are behaving, and then we can reduce the factors coming from uncertainty on material performance.
I2: With sensors inputs, what does the modeling and monitoring look like?
Banthia: Once you have sensors on a structure, it can generate terabytes of data. You collect so much data, and you need to analyze it. Generally, the infrastructure owners would contract out monitoring. An engineering company that understands the bridge performance would plug that data into the bridge model to understand an anomaly. Because you’re getting so much data, a lot is within an acceptable range. Within the wide range of performance, if the data is within that range, things are fine.
If you get an anomaly in a specific area, you feed it back into the model to understand what part of the bridge is in trouble and potentially what repair needs to be performed. The sensors trigger a more-intensive condition assessment when you get data that falls outside of the range. We call that anomaly assessment.
Bridge models are fairly developed. The structural side isn’t that complicated, as we understand structural design and have good structural models. It’s the input in terms of what the loads are and the conditions that are uncertain. Once you feed the sensor data into a model, if the performance data falls outside the range allowed, then you know something wrong is going on.
It may not even be obvious visually. That’s the real power of this approach, because only the sensor would tell you.
I2: Is there a move to mandate and use more sensors on bridges?
Banthia: In some countries (Denmark, for example) they are already requiring sensors on structures of strategic importance, and I’m pretty sure that’s where we’re heading. Any structure of critical importance, an arterial bridge for example, absolutely needs to be monitored.