1. call 911, that will be your best witness. Pictures of damage could have been made anywhere else, a Police report would have been your best defense.
2. instead of wiping you should have grabed a water hose at the construction site and rinse it, you should know better then that not to ever wipe off dirt.
But really sorry to hear, what must have happened was that someone has blowing off the concrete lines and was too stupid to see where the concrete was going, good luck man.
Still letting it all sink in... and loving every minute of it!!