There are a number of pressure treating methods used today. The one I have read the most about is the typical "pressure" process by which lumber is placed in a cylinder and it is pressurized with the chemicals inside.
But that is a general description for what really has a number of different kinds of pressure treating processes. The ones I have heard about are the a full-cell process, a fluctuating pressure process and the Boucherie process.
That is the extent of my knowledge. You will have to research further at your end as technology continues to evolve.
I am building a 10'x12'deck (not attached to a ledger board). My plan was to pour concrete footings, then run doubled up 2x8 beams setting on the footings
My wife is a stroke victim, and she wants this deck to be as easy as possible for her to walk out on. She would like it to be as high as possible, with