Yes, the detail maps are 2 extra textures used for close up detail, one gives it the asphalt look... the other gives the cracked, rough look. Both are controlled by a RGB mask. If you use only the red channel, you only get one detail map to show, but if you start to use another colour of that mask, say blue, then you can get the crack detail map to show as well.
The mask is fairly simple, in photoshop anyways... you start with a black texture, then in the channels tab, you'll see 3 channels, RGB. Select the channel you want to use, then start colouring it. 100 percent white on a channel means that channel is 100 that colour, it will show the detail map 100 %.
50% (grey) on another channel, means you'll get another detail map to blend in around 50%.
And so on... its one of the more complicated shader setups, but it's the one that makes things look awesome!