I don't have a hard number on the density, but the stuff is light - the hauler uses tridem trucks with 20' boxes and high box sides and a load is maybe 15 tons.  Our local ash we usually spread at 3x the recommended lime rate, the price is right (free) so for the cost of spreading getting rates exact isn't a big deal.  I have never noticed any crop problems even on the site where the ash is stockpiled.

I'd have to dig up the numbers for detail but by my figuring the ash I spread this past spring was worth around $30/ton just for the potassium value, the liming value and other nutrients would be in addition to this.