If the road freezes over, you don’t always have to spread salt. Researchers at Drexel University in Pennsylvania have developed a concrete that thaws itself. To do this, they introduced paraffin into the concrete. The waxy material melts at temperatures above 5.5 degrees Celsius and absorbs the heat from its surroundings. This phase change allows it to store the absorbed energy for as long as desired without loss. If the temperature drops below the melting point, it becomes solid and releases this heat again.
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The research team tried two methods of introducing the phase change material into the concrete. The first method was to dip porous aggregate material in liquid paraffin before adding it to the concrete. The second method was to add paraffin-filled micro-capsules directly into the concrete.
The concrete slabs with the different approaches in the test.
(Bild: Drexel University)
Comparison of methods for snow and ice
Using these two processes (plus a batch of conventional concrete for comparison), the team produced concrete slabs in late 2021 and exposed them to the weather. Since then, the half-square-meter slabs have endured 32 frost events and five snowfalls. Meanwhile, cameras and heat sensors monitored the plates. The result: The panels produced using the first method were able to maintain a surface temperature of 6 to 13 degrees for ten hours after the onset of frost. That was enough to melt away a layer of snow several centimeters thick. The plates with the paraffin microcapsules released their heat more quickly, but could only maintain it for about half as long. The researchers’ explanation: The porous material ensures that the paraffin only melts below its normal melting temperature, namely 3.9 degrees Celsius. The microcapsules, however, gave off their heat at just 5.5 degrees.
The self-heating concrete panels are not only safer, they also last longer because they suffer less frost damage. However, with more than five centimeters of snow, the concrete mixes were overwhelmed. Even if there is not enough time to heat up between the frost phases, the material reaches its limits. Next, the researchers want to collect more data on the durability of the new concrete.
(grh)
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