qmorr....first of all, saw-cut joints are typically control joints, not expansion joints. There's a difference.
As for sealants, most pavement joints are either polymer modified asphaltic or urethane. Silicone is usually not used for pavement joints.
Pre-formed EPDM or other synthetic "rubber" joint seals are used as well.
Please note that there is little need for "expansion joints" but plenty of need for control and isolation joints, all of which should be sealed against water intrusion.