2 of the 6 6" 5/8 expansion anchors have failed in that the nut just turns with the bolt and doesn't tighten. I'm actually more concerned about how I pull them out as they seem to have expanded enough that a crowbar doesn't budge them.
Bob:
It is difficult to troubleshoot installation problems from afar without more information such as the embedment depth, base material type and strength, age of base material, thickness of base material, anchor spacing and edge distance, tools used during installation, etc. With that said, my initial thoughts regarding the anchors that failed to achieve installation torque: damage to the anchor threads is causing the nut to be bind, voids in the base material and/or excessive/prolonged force used to hammer the anchor into the hole.
Typically expansion anchors cannot be removed without damaging the base material after they have been installed in the hole. Many Customers will diamond core drill around the failed expansion anchor to remove it and use an adhesive anchor system such as Hilti HIT-RE 500 V3 to reinstall an anchor of the same diameter.
Feel free to send me more information by posting to the Ask Hilti forum or sending an email to teamaskhilti.us@hilti.com.
Regards,
Randy