huangyhg

epoxy for doweling rebars in existing concrete
based on my experience, i do not have major problems with epoxy for dowells in concrete. in practice, we usually use hilti anchors or hilti epoxy with rebars. however, the dowel-in length must be followed according to hilti manual. i had a job failed in pull out force of rebars because the contractors did not dowel deep enough in concrete to develop sufficient bonding force for rebars. be carefull, when you design hilti epoxy system and also specifically require the min. dowel in length for contractors.
a few years back, we used 5000 hilti c-100 concrete/brick anchors in the earthquake retrofit on one of the buildings at usc. the los angeles county inspectors did a 10 percent pullout and all passed. with this many to install, we used an pneumatic roto-hammer which aided in cleaning out the holes and the pneumatic hilti injector tool (expensive) which eased the work load. in my experience, failure is caused by not following the instructions to brush out and blow out the holes before injecting the epoxy. with the brick anchors it is difficult not to drill deep enough because the cages stick out too far, but with rebar it is possible and you must have concientious and qualified workmen doing the installation. newer epoxies are now being used and you seldom see the c-100 any longer. as an engineer it would seem a certain redundancy in this type of installation would be of benifit.
rod
epoxy anchors are not specifically covered in building codes yet. aci is in the process of developing code requirements for various types of post-installed anchors for the next code cycle. in the meantime, such anchors are covered by icbo or nes evaluation reports.
the quality of epoxy anchors is generally very good. one thing to keep in mind is that the epoxies typically lose significant strength at high temperatures. so be careful if you are using them in fire-resistive construction.
also, curing times in cold weather is a problem. do not use epoxy in weather colder than 40 degrees f. another thing is clean out of holes. if the holes are dirty, the bond strength is reduced.
now, hilti has a new product the hit re 500 epoxy they say can cure at temps down to 23 deg f. they also have a new bolt that can be placed in dirty holes. i think its called the hit-tz bolts.
so a remark is that maybe when non redundant to an independent structural system these adhesive connections should be forbidden when they may be affected by (fire) heat...to what extent, or under which protection, or to what temperature?

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