Jinan, China – Asphalt is commonly used for road surfaces because it is quick to install, is comfortable for drivers, and its maintenance costs are low. However, it has its drawbacks – it is prone to cracking, pitting and rutting when subjected to extreme temperatures and precipitation, as well as when heavy loads are driven over it.
One way to improve its performance is to include polymeric materials in the mix, particularly polyurethanes, as they can increase the asphalt’s deformation resistance. It works because the isocyanate groups can react with hydroxyl and carboxyl groups in the asphalt to form carbamates. Hydrogen bonds also form.
Now, a team at Shandong Jianzhu University’s School of Transportation Engineering has looked at the potential of high-dosage PU-modified asphalt. They investigated the mechanism of modification and mix performance, and how the PU impacts the functional groups and microstructural morphology of the modified asphalt.
Earlier studies had shown that 40%, 50% and 60% PU content improves asphalt performance, so they used these proportions in their thermosetting PU-modified asphalt.
The two materials were first preheated to 120°C before the PU was added to the matrix asphalt, and subjected to high-shear mixing for 10min at 120°C. A polyol hardener was then added, and the mixing continued for a further 10min, giving the modified asphalt.
They also found that at a PU content of 50%, the curing reaction was most effective. This is beneficial for the bonding performance between asphalt and aggregate, enhancing its water stability.
Rutting tests, low-temperature bending tests and freeze-thaw splitting tests were carried out on the different mixtures. Its flexural tensile strength and strain were significantly improved, and the splitting strength before and after freezing and thawing is also somewhat better.
The work has been published in the journal Coatings.
