According to data from the National Highway Administration in the United States, the country spends up to $2.3 billion annually on snow and ice removal operations on roads, in addition to spending millions of dollars to repair roads damaged during cold weather.
However, on the campus of Drexel University in Philadelphia, there are two inconspicuous 30x30-inch stone slabs that have not needed to be shoveled or treated with deicing salt for over three years. Researchers at Drexel's College of Engineering reported the scientific principles behind this special concrete in the Journal of Civil Engineering Materials on March 18th. It is mixed with phase-changing materials, which allows it to self-heat when it snows or approaches freezing temperatures.
The leftmost is ordinary concrete, and the two on the right are high-end concrete. Image source: Dresel University. In winter, the road surface experiences a cycle of freezing and thawing, which causes the concrete surface to expand and contract, putting pressure on its structural integrity and eventually leading to destructive cracking and spalling.
Amir Farnam, Associate Professor at Dresel University's College of Engineering, said, "One way to extend the service life of concrete surfaces, such as roads, is to help them maintain a surface temperature above freezing in winter. Our work is to study how to incorporate special materials into concrete to help it maintain a higher surface temperature as the ambient temperature drops."
Over the past 5 years, this team has been developing elastic concrete mixtures for cold weather, but previously only in controlled laboratory environments. The latest achievement proves its feasibility in natural environments.
They used high-end phase change materials - 5°C phase change wax to transform the concrete. The solidification point of ordinary liquid paraffin is about 45°C, while 5°C phase change wax transforms from liquid to solid when the temperature is below 5°C, releasing heat during the phase change.
The researchers designed two ways to transform the concrete. One is to mix the phase change wax into porous lightweight aggregates before making the concrete and then make the concrete using wax-absorbed aggregates. The other is to directly mix micro-wax particles into the concrete.
They poured one concrete slab using each method and used a regular concrete slab as a control. Since December 2021, the three concrete slabs have been placed outdoors, and a total of 32 freezing and thawing cycles have occurred in the following two years, including 5 snowfalls of more than 2.5 centimeters.
Through long-term monitoring, they fo...
