Speed Asphalt Cooling with Dry Ice
Asphalt paving work looks rough-and-ready, but it is actually a ballet. The hot mix has to leave the plant at just the right temperature to arrive at the job site ready for spreading. The paving machine needs a constant supply of asphalt from the trucks. The rollers must compact the asphalt effectively to get long-lasting pavement.
Highway agencies establish contract requirements regarding the acceptable compaction and final density of the asphalt paving. This is tested by cutting cores from the new paving for examination in a lab. The coring requirements are very particular in order to prevent damage to the core sample. To cut an undamaged core for testing, the asphalt must cool down. This time delay can be costly to the contractor if inadequate compaction is discovered much later in the lab.
To speed the cooling process and core the paving sooner, contractors use dry ice. The dry ice is not placed directly on the newly-rolled asphalt, because the thermal shock from the extreme cold would put micro-fractures in the sample core. Usually wet ice, left in a plastic bag to keep the asphalt surface dry, is placed between the dry ice and the pavement area. In addition, a mobile testing lab is positioned at the job site to speed up field evaluations.