Researchers from Drexel University Philadelphia, Pennsylvania, Purdue University West Lafayette, Indiana, and Oregon State University Corvallis, Oregon, USA, have made a discovery that could create roads that melt off ice and snow during winter storms. Their secret? — Adding a little paraffin wax to the road’s concrete mix.
Led by Yaghoob Farnam, PhD, Assistant Professor-Drexel University College of Engineering, the researchers explain how substances like paraffin oil—known in chemistry as “phase change materials” (PCMs)—can be used in concrete to store energy and release it as heat when a road needs a melt-off in a paper titled “Incorporating phase change materials in concrete pavement to melt snow and ice” recently published in the journal “Cement and Concrete Composites”.
Keeping roads open to travel is a persistent challenge during winter months, but efforts to make them safely passable—including the constant use of snow plows, deicing chemicals and road salt—tend to deteriorate the surface. The chemicals and road salts currently used to melt snow and ice can also have a deleterious environmental impact when surface runoff carries them into nearby ecosystems (Pennsylvania alone dumps more than 900,000 tons of it on roads each winter). So, researchers have been searching for a much more eco-friendly winter option for quite a long time.
The research group(s) are among the first to demonstrate that using PCMs as an environmentally friendly alternative can be just as effective as the standard salting and scraping methods. “PCMs can be incorporated into concrete using porous lightweight aggregate or embedded pipes. When PCM transforms from liquid to solid during cooling events, it can release thermal heat that can be used to melt ice and snow,” Farnam said. “By inhibiting the formation of ice and snow on the pavement or bridge surface, the use of PCMs may reduce or eliminate the need for deicing chemicals/salts, snowplowing or both—thus saving money and positively influencing the environmental impact of such operations.”
Paraffin oil, a common ingredient in candles, wax polishes, cosmetics and water-proofing compounds, was their material of choice for this endeavor because it is organic, widely available, chemically stable, and relatively inexpensive. Like all phase change materials, paraffin oil releases thermal energy when it changes its physical state, which means as temperatures drop and the oil begins to solidify it releases energy through latent heat of fusion. This means paraffin oil can be tailored to embed deicing capabilities in a road surface so that it becomes thermally active during snow events or when deicing is needed.
To test its snow and ice-melting ability, the team created a set of concrete slabs:
- Slab One: with paraffin-filled pipes inside
- Slab Two: containing porous lightweight aggregate that had been infused with paraffin
- Slab Three: reference slab without paraffin
Each was sealed in an insulated container and then covered with about five inches of lab-made “snow”. Both of the paraffin-treated slabs were able to completely melt the snow within the first 25 hours of testing, while the snow on the reference sample remained frozen.
1st Experiment: Temperatures inside the boxes held between 1.7-6.7°C (35-44°F):
Slab One with the paraffin-filled tubes melted the snow slightly faster than Slab Two composed of paraffin-treated aggregate. Farnam suggests that this is because the paraffin inside the tubes is able to solidify more quickly, thus releasing its energy. This is due to the regular diameter of the pipes, while the diameter of the pores of the aggregate vary in size.
2nd Experiment: Ambient air temperature in the box was lowered to freezing o°C (32°F) before the snow was added:
Slab Two paraffin-treated aggregate was more effective than Slab One with embedded pipes. Because the capillary pore pressure delayed the freezing of the paraffin, it allowed it to release its heat energy over a longer period of time. “The gradual heat release due to the different pore sizes in porous light-weight aggregate is more beneficial in melting snow when concrete is exposed to variety of temperature changes when snow melting or deicing is needed,” Farnam said. “We believe that using porous lightweight aggregate can be potential way of incorporating phase change materials in concrete as it is easy to be implemented in practice and can cover environmental conditions of various locations in the US dealing with snow, especially melting snow or deicing in roads and bridges in the Northeast.”
One of the first uses of this infrastructure technology could be at airports, where keeping runways clear of snow and ice is vital and a perpetual challenge in the winter. The Federal Aviation Administration (FAA) supported this research as part of its “Heated Airport Pavements Project” in its Partnership to Enhance General Aviation Safety, Accessibility and Sustainability program.
Farnam concluded, “Additional research is needed to further understand other factors influencing concrete constructibility, including concrete fresh and hardened performance when the concrete contains phase change materials, and the PCM’s thermal performance in different locations in the U.S. But before it can be incorporated to reduce deicing chemicals used or used as a new deicing method improve the safety of roads and bridges, we will need to better understand how it affects durability of concrete pavement, skid resistance, and long-term stability.”
For the article (and Home page photo), please go to: http://drexel.edu/now/archive/2017/September/self-melting-concrete-roads/
For the paper abstract (and to purchase the paper) titled “Incorporating phase change materials in concrete pavement to melt snow and ice”, please click on image to left, or go to: http://www.sciencedirect.com/science/article/pii/S0958946516307417.
For the VIDEO titled “VIDEO: Wax On, Melt Off—Melting Snow Using Phase Change Materials (PCM) in Concrete” posted just before this article, please go to: https://www.concretepavements.org/2017/09/19/video-wax-on-melt-off-melting-snow-using-phase-change-materials-pcm-in-concrete/