I am reliably informed that they have a problem at Alf Barbagello racetrack.
Apparently, some time ago there was a crash during a truck race, and a truck deposited some diesel on the road, right at the end of the main straight.
They tried to clean it up, but every time it rains, it comes to the surface. This of course causes a problem, as not only is the track slippery with the water, but the film of diesel on top makes it extra slippery.
The reason this happens, of course, is that the diesel will soak into the bitumen when it’s dry. When it’s wet, however the diesel will float on the water which is why it comes to the surface and causes the problem.
It’s going to be impossible to remove when it’s dry, as it is right down in the pores of the bitumen. So, here is how you get rid of it.
Soak the relevant part of the race track with water so that there is water sitting on top. Now sprinkle on top copious amounts of gypsum (plaster of Paris). This is a very porous material that is a strong adsorbent. As the diesel comes to the surface the plaster will soak up the water, and the diesel will stick to that gypsum. So when it dries, it will stay in gypsum and not go back down into the bitumen.
The gypsum can then simply be swept off, solving the problem.