Removing Carpet Adhesive from Concrete?

Spray liberally with WD-40 and let it sit overnight.
Spray again in the morning and it will come off with a putty knife.

Try cider vinegar. I have used it to get old glue off wood floors that had tile glued to them, it worked great. In some areas I heated it up on the stove with rags then let the rags soak on the floor for about a half hour.

Having tried everything under the sun, the best answer I found was first to use a hand scraper to take off the top layer, then follow up with Mister Clean (or some other cleaner) and a power scrubber. Next, you mop up the goop that's left and in the end, have clean concrete. It's a lot of work but the stuff comes off without the incredible mess encountered with liquid chemicals.