An anchor bolt is a unique type of fastener that’s designed to secure an object or structural component to a concrete surface. They don’t feature the same long shank with a flat tip as other bolts. Rather, anchor bolts feature a unique design that allows for embedding inside of concrete. There are several types of anchor bolts, however, each of which is used for a different purpose.
A cast-in-place anchor bolt is a type of anchor bolt that lives up to its namesake by being cast inside of concrete. It’s similar to a traditional bolt but with a few nuances. Cast-in-place anchor bolts almost always have a hexagonal head, whereas traditional bolts can have a variety of heads. More importantly, cast-in-place anchor bolts are installed upside down. The head is inserted into an open cavity of the concrete, after which it’s cast in place. Casting requires the use of concrete. Concrete is poured in the cavity so that it encompasses the anchor bolt.
Another common type of anchor bolt is post-installed. Post-installed anchor bolts consist of a similar design as cast-in-place anchor bolts. They both feature a hexagonal head, and they are both installed upside down with the head first. The difference is that post-installed anchor bolts are installed in a pre-drilled hole, whereas cast-in-place anchor bolts are installed inside of a cavity that’s later filled with additional concrete.
There are also expansion anchor bolts. Expansion anchor bolts are those that expand when installed inside of concrete. To use an expansion anchor bolt, you’ll need to drill a hole into the concrete surface. You can then install the expansion anchor bolt inside of this pre-drilled hole. As the expansion anchor bolt enters the hole, it will expand. This expansion helps to secure the anchor bolt — as well as the structural component or object to which it’s connected — in place. Technically speaking, an expansion bolt is a type of post-installed anchor bolt because it’s installed in a pre-drilled hole.
Most anchor bolts can be classified as either cast-in-place or post-installed. Cast-in-place anchor bolts are the most common. They are installed inside of a cavity of a concrete surface, after which they are cast in place. Post-installed anchor bolts, on the other hand, are installed inside of a pre-drilled hole. Expansion anchor bolts are considered post-installed. Other types of post-installed anchor bolts include undercut, self-tapping and power-actuated.