A road’s base layer is made entirely from aggregate. Generally 12 inches deep and of various sizes of aggregate from 1” down to fines.
The base layer distributes the weight of vehicles onto the sub base layer of the roadway.
1 or 2 aggregate sizes are mixed with 2% to 3% water in the pugmill mixer to improve compaction.
Most state road departments require mixed material to be stored in a surge hopper to prevent aggregate segregation before it enters the dump truck