Why Mixing More Recycled Rubber Into Asphalt Changes How It Breaks Down Over Time

A new study looked at what happens when a lot of waste tire rubber gets mixed into asphalt. Old tires create a big mess in landfills, so scientists wanted to see if huge amounts of ground rubber, between thirty and fifty percent of the mix, could still make good road material. They wanted to understand how this rubber-asphalt blend ages when it sits in the sun and air for a long time.

The research team used several lab tests that mimic how asphalt breaks down. One test, called RTFOT, copies the effects of hot mixing during construction. Another test, named PAV, copies what happens after years on the road. They also used powerful machines like DSR and BBR to measure how the asphalt stretches and bends. Other tools, like TD-GC-MS and FTIR, helped them see what chemicals were floating off the material as it aged.

Here's something interesting they found. When they used fifty percent rubber, the blend showed a strange behavior. At first, the rubber bits tended to clump together and separate from the asphalt, which is bad for roads. But after the aging process kicked in, something unexpected happened. The heat and oxygen made the rubber network swell up and form new connections inside. This actually locked everything in place. The high-temperature performance got much better, not worse.

But there was a catch. All that dense rubber created a new problem in cold weather. When temperatures drop below freezing, the material couldn't flex and relax as easily. Think of it like a rubber band that gets too stiff. The tight network left very little room for the asphalt to move, so stress built up instead of being released.

The scientists also discovered that the rubber acts like a shield for the asphalt underneath. During aging, the rubber breaks down first, soaking up most of the damaging energy from heat and oxygen. This protects the base asphalt from getting hard and brittle too quickly. As time goes on, the way the material fails completely changes. Instead of the asphalt itself cracking apart, the rubber pieces start pulling away from the asphalt. Eventually, everything mixes into one uniform blob. This research opens up new possibilities for designing roads that last longer while recycling way more old tires.