THIS SAMPLE, a 14-inch-tall layer cake of asphalt, gravel, and brick, was extracted from Turn 4. It was still undergoing testing in April, a month before the Indianapolis 500. Testing is routine, but not done on an annual basis. The last time a core sample was taken was in fall 2017.
Over time, the track changes as it expands and contracts. Several years ago, engineers used a tool to laser-measure the surface and establish a baseline. “Now we can see the tiniest bit of movement in the track.” That helps officials head off potential problems and keep the track in racing shape.
Workers laid the original bricks from September to December in 1909, which provided the racing surface for the very first Indianapolis 500 in 1911. “The front stretch remained brick until the 1960s when they first put asphalt over the entire racetrack.”
“Most of those 3.2 million bricks that were laid in the fall of 1909 are still underneath there.” As the mortar between the bricks erodes, water finds a way into the void. “You can see places where the track is expanding and contracting, especially in the wintertime.”
A 6-inch diameter drill is used to cut the track samples. A stream of water keeps the circular bit from overheating. “We know when we’ve reached the brick [level] because the water coming out changes from the dark asphalt color to that red-brick color.”
Experts fill the sample holes with the same asphalt mix found in the top layer. In some parts of the track, “not all of the layers are there. Sometimes when they went to resurface, they might have removed an entire layer in certain areas.”
Because some layers have been completely removed over time, it can be difficult to establish a full history of the racing surface from one sample. To help, IMS officials work with asphalt experts at an Indianapolis company called The Heritage Group.
The IMS is one of Indiana’s crown jewels, but several layers down, there’s a gravel-and-asphalt mix that was produced by a plant in Kentucky. “Over time, we’ve come up with this completely different mix. It’s got a bit of metal inside of the mix itself to help it have a longer life.”
Last time the track was resurfaced was in 2004. “It’s been 18 years, which is pretty amazing especially when you consider our Indiana summers and winters.”
A case outside Boles’s office contains a fully intact sample extruded in 2017. “It’s a fascinating conversation piece.”
