No, the dumpster. The concrete was brand new and very grippy. We didnt want to melt the blacktop and didnt want the car to get out of control if a tire blew (especially with camera people and Tim spraying the water around). For safety'* sake we strapped it down. The water was sprayed in an effort to keep the heat of the tires down so they would not catch on fire or explode.
Towards the end I could feel the car floating and bouncing which to me meant a tire was about to blow so thats why I got out of it.