In North American regions with cold climates, snowfall, and freeze–thaw cycles are pretty common during winter seasons. This results in the accumulation of snow on concrete roads and flatwork and concrete freeze-thaw damage.
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However, on Drexel University’s campus, there is a section of concrete that showcases the future of frost-free sidewalks and highways. This section is located right next to the university’s parking lot.
It involves two 30-inch-by-30-inch slabs that have been clearing snow and freezing rain on their own, without having anyone shovel, salt, or scrap for as long as three years. But it’s not a miracle; what it is is self-heating concrete.
So, last week, researchers at Drexel’s College of Engineering reported on how they created this special concrete that can warm itself up when the temperature drops to freezing or it snows.
Published in the Journal of Materials in Civil Engineering, the paper discusses the development of self-heating concrete using low-temperature phase change materials, or PCM.
These experiments were conducted in Drexel University’s Advanced Infrastructure Materials (AIM) Lab. To conduct these experiments, the US-based Compass Minerals provided the financial support, while MicroTek Laboratories provided the materials for research purposes.
The study was conducted by Amir Farnam, Ph.D., an associate professor; doctoral student Robin Deb; undergraduates Nishant Shrestha, Kham Phan, and Mohamed Cissao; and doctoral candidates Sharaniaya Visvalingam, Angela Mutua, Yousif Alqenai, and Parsa Namakiaraghi, all of whom belong to the College of Engineering.
With this self-heating concrete, the goal, as Farnam explains, is to prolong the operational life of roadways and various surfaces. Specifically, it aids these concrete surfaces in maintaining temperatures above freezing during cold climates. The idea here is to foster resilient infrastructure in the US’s northern regions, where states annually invest approximately $2.3 billion in snow and ice removal operations.
So, in order to prevent freezing and thawing as well as reduce the need for plowing and salting to keep the surface from crumbling, the new experiment introduces special metals in the concrete that help it maintain a higher surface temperature when the climate changes.
This material has been in development for about half a decade with the aim of reducing the freezing, thawing, and salting that negatively impacts roads and other concrete surfaces. Self-heating concrete is reported to have the ability to melt snow and slow down or prevent the formation of ice for an extended period of time.
Up until now, self-heating concrete has shown great potential and success in a controlled lab setting, but now its viability has also been demonstrated in the real world, the outside natural environment. And it showed that the self-heating concrete can actually melt snow without needing any human assistance or heating systems. It can actually do it on its own using only the environmental daytime thermal energy.
“This self-heating concrete is suitable for mountainous and northern regions in the USUS, such as Northeast Pennsylvania and Philadelphia, where there are suitable heating and cooling cycles in winter.”
– Farnam
The Low-Temperature Phase Changes Material
The material in question, which helped the study achieve self-heating concrete, is low-temperature liquid paraffin. This is a phase-change material (PCM), meaning when the ambient temperature falls to ∼0°C or 32 °Fahrenheit, it releases desirable amounts of heat when it turns from its room-temperature state of liquid to a solid. This leads to the gradual melting of the accumulated snow and ice.
While the group has previously reported that incorporating the material into the concrete activates heating just as there’s a drop in temperature, the latest research involved evaluating the performance of self-heating concrete under both laboratory thermal conditions and outdoor real-time conditions during the fall and winter seasons.
The program’s purpose was to optimize concrete mix designs for maximum PCM incorporation and characterize the thermal properties of PCM-mortar examples using LGCC. LGCC, or longitudinal guarded comparative calorimetry, is a test device used to quantify the thermal properties and heat flow of concrete specimens.
Additionally, the idea has been to have large-scale concrete slabs treated with phase-change material outside the laboratory in natural conditions to assess how efficient they are in melting snow and their thermal performance in real-time against freeze-thaw events. The events refer to when temperatures fall enough to freeze water, which happens at 32°F or 0°C, and then increase enough for it to thaw again.
Now, to integrate the material into concrete, the team made use of two methods. This included microencapsulated PCM (MPCM), where micro-capsules of paraffin are directly mixed into the concrete. The other approach was submerging the liquid phase-change material in porous lightweight aggregates (PCM-LWA), under which fragments of small stones that make up concrete were treated with paraffin. These small stones and pebbles absorb the liquid paraffin before they are incorporated into concrete.
In their experiment, the researchers used three slabs: one poured using the MPCM method, the second using the PCM-LWA, and the third having no phase-change material as a control.
These slabs have been confronted with the natural climate since Dec. 2021. During this time, all three experienced 32 freeze-thaw events, with temperatures falling below freezing. In these first two years, they also faced five snowfalls of an inch or more. To monitor the temperature and the slabs’ behavior, the team used cameras and thermal sensors.
When air temperatures dipped below freezing, researchers found that the PCM slabs maintained a surface temperature between 42 and 55 degrees Fahrenheit (5.56 and 12.78 degrees Celsius) for up to 10 hours. This is enough to melt a couple of inches of snow. However, this happens at a slow speed, about a quarter of an inch of snow per hour. While not warm enough to melt heavy snow, it can help keep the road surface free of ice and increase transportation safety.
This is beneficial in preventing the deterioration of roads as periods of extreme cooling and then warming cause a surface to expand and contract in size, putting a strain on its structural integrity and potentially leading to cracking and spalling over time. All this creates a vulnerability that ultimately leads to the failure of the structure from the inside, which needs to be avoided.
“One of the promising findings is that the slabs with phase-change materials were able to stabilize their temperature above freezing when faced with dropping ambient temperatures.”
– Deb
In addition to helping extend the life of infrastructure, it can also save money on road maintenance. According to estimates by the National Highway Administration, millions of dollars are spent repairing roads damaged by winter weather. Furthermore, by removing the need for salting, states can not only save on labor and salt costs but also prevent cars from rusting. This approach also helps to avoid polluting aquifers with excess salt, ensuring they remain safe for human use.
Gradual Progress, Potential for Growth
The group examined the self-heating concrete in different scales and found PCM to be showing satisfactory supercooling, long-term thermal stability, and high enthalpy of fusion. Overall, both the concrete slabs with the material showed positive snow-melting capabilities while lowering the number of freeze-thaw cycles in winter, as per the study results.
The slab treated with porous lightweight aggregates (PCM-LWA) was found to be better at decreasing the number of freeze-thaw (F-T) cycles. This was because of the relative disbursal of the PCM within the pores and the undercooling phenomenon created by the confinement pressure of the LWA pore network.
In turn, this allowed the release of latent heat gradually. The undercooling here generates phase transformation in a larger range of low-temperature, that is, 3.94°C to −13.04°C or 39.09°F to 8.52°F. Hence, the PCM-LWA method was found to be more effective in melting snow at this low-temperature range.
Meanwhile, the “one-shot” heat release phenomenon of MPCM concrete helps it melt snow at a fast pace. The slab treated with microencapsulated phase-change material (MPCM) while able to heat up more quickly, could only maintain the warming for half as long as LWA-PCM.
So, while PCM-LWA slabs were able to hold the release of its heat energy until the material reached 39 degrees Fahrenheit, MPCM started releasing its heat just as the temperature reached 42 degrees, contributing to its relatively shorter activation period.
As a result, the team stated that the PCM-LWA method is better suited for de-icing applications at sub-zero temperatures.
Despite both applications’ ability to raise concrete temperature between 53 and 55 degrees Fahrenheit, the rate of snowfall and the ambient air temperature before a snowfall affect both PCM-LWA and MPCM performance.
Pavements incorporated with PCM were found to be unable to completely melt heavy snow accumulation (larger than 2 inches), but below this, they can melt snowfall “quite effectively.” They actually start defrosting the snow the instant it begins to collect.
According to Deb, the gradual release of heat can successfully thaw the concrete’s surface, eliminating the need for pre-salting prior to heavy snowfall. However, it must be noted that the material needs some recharge time between snow or freeze-thaw events to work effectively. If it doesn’t return to its liquid state at this time, then the performance may diminish.
Now that the team understands how concrete incorporating PSM behaves in nature, it will work on improving the system to optimize it for longer heating and greater melting. Researchers need to collect more data to understand the material’s long-term effectiveness and conduct a study to determine how this method might extend the concrete’s lifespan.
This is just the latest advancement in improving the infrastructure while saving the environment as organizations and governments work on finding better ways to handle the cold and hot seasons. Recently, we reported how scientists at the University of California detailed how to cut heat and cooling costs through adaptive roof tiles. The tiles feature a radiative switch or a passive thermoregulation device to respond to a range of temperatures.
Another solution has been an all-season smart-roof coating developed in Berkeley Lab’s Materials Sciences Division that keeps homes warm during the winter and cool during the summer without requiring natural gas or electricity. It utilizes a new material called a temperature-adaptive radiative coating (TARC) that automatically turns off the radiative cooling in winter to ensure there is no overcooling and energy waste. All of this shows a brighter future ahead for us and our planet.
Working on Winter Maintenance
Now, let’s take a look at some of the names in the industry that offer deicing solutions and are involved in finding more innovative options:
#1. Clear Roads
This program brings together transportation professionals and researchers from all over the country to drive innovation in winter maintenance. Clear Roads evaluates materials, equipment, and methods in real-world conditions to find the best technologies and solutions to help save money, increase efficiency, and improve safety.
In its 2024 TRB Annual Meeting, the program focused on topics like the implementation of salt stockpile inventory using LiDAR measurements, salt sustainability, artificial intelligence, and roadway friction modeling. It also covered predicting winter road surface conditions using a data-driven approach, a winter pavement temperature prediction model based on transfer learning and long and short-term memory neural networks, developing a prototype of a digital twin for winter road maintenance, the future of road weather, and more.
#2. Cargill
The company provides deicing solutions for roads and highways. Cargill’s effective winter maintenance solutions minimize environmental impact as well as the associated costs. The company’s wide range of products includes granular deicers, anti-icers, automated brine-making systems and additives, and solutions for pavement overlay.
In the second half of last year, it was reported that the company has been looking to offload a selection of its US deicing salt businesses, which at the time had been generating roughly $40 million of EBITDA on about $375 million in revenue.
The assets the company is looking to sell consist of facilities that mine, process, and transport deicing salts to municipalities, government agencies, and private commercial businesses across the nation for use on roadways during winter storms. This came after Cargill closed its third salt mine in Avery Island, La., in 2022.
#3. Clariant
This one offers aircraft deicing, a growing sector projected to grow to $1.83 billion over the next seven years at a CAGR of 5%. North America is leading the charge of this growth thanks to the region’s robust aviation industry. Aircraft deicing systems are critical for safe take-offs and landings.
In addition to aircraft deicing, Clariant offers recycling solutions and assistance to customers to overcome operational difficulties in adverse weather conditions on the runway. For this, it has developed extremely effective Deicing Fluids that keep the surfaces of aircraft free from snow and ice. The company also specializes in de-icing the runway and anti-icing chemicals.
Conclusion
So, as we saw, self-heating concrete is a big invention that can be used to construct pavements, driveways, bridge decks, and many other types of flatworks. The product developed also helps improve concrete durability and service life, saving money on road maintenance, labor, and product usage while helping prevent cars from rusting and excess salt from polluting aquifers. Research like this is not just good for humans but also for the environment, helping enhance our lives while protecting the ecosystem.
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