All of the piers and abutments have been made from high-strength mortar mix.  You can see the forms I made here.  They are made from 1/2" plywood smooth on one side.  Drywall screws were used to hold them together.  Don't skimp on the number of screws you use.  80lbs. of mortar puts an awful lot of pressure on the forms!  The abutment form above has been filled with mortar and is waiting to be removed from the form.  One lesson I learned is to not open the forms too soon or the mortar will crumble.  I wound up pouring the mortar one day and waiting overnight before removing the form.

In the upper left you can see the empty form for the piers.  It has been lined with aluminum flashing as it will be used many times over.  There is a 3 degree taper built in.  Only one side of the form has to be removed and then the pier will with a little effort just drop out.

Just to the left of the abutment form is the small form for the pier caps.  The caps are only about 3/8" thick and slightly fragile.  I had a few break on me in the forming process.