A fastener or an anchor bolt is a device that is used to attach objects or structures to concrete. Though there are many types of anchor bolts and designs, they are mostly proprietary to the manufacturing companies. The fastener usually comprises a threaded end, which can be attached to a nut and washer for the external load. Anchor fasteners can be categorized into two types essentially, mechanical anchor fasteners and chemical anchor fasteners.
Let us now delve further to understand the different types of anchor fasteners available and how they work.
Types of Anchor Fasteners
Mechanical Anchor Fasteners
Mechanical anchors physically leverage friction anchor themselves in place. Often, the base of an anchor is designed to expand in diameter when it is inserted into the hole, such that, the expansion strongly grips the base material and wedges the anchor firmly in place. The force used in pushing the anchors the screw in place and prevents it from falling out.
In the world of mechanical anchors, the diameter of the hole drilled plays a critical role. It is important that the hole diameter is just right, because, if it is too large then it fails to sufficiently grip the sides of the hole and thus collapse when it is put to loading.
Chemical Anchor Fasteners
Chemical anchor fasteners come with a special injectable adhesive that helps to stick the anchor into the hole. The most load-affecting and time-consuming step in the installation process is cleaning the hole before injecting adhesive. Therefore, Hilti has brought in a range of tools that can help install adhesive anchors more quickly and reliably using SafeSet™ Technology. It includes hollow drill bits, vacuum cleaners, HIT-HY 200 and the HIT-Z anchor rod that can help you to accomplish tasks effectively. Once the hole is cleaned of all dust and debris, it is then filled with the chemical adhesive.
The chemical is then left to set. Quick setting chemicals may set in an hour, while the more common ones may take up to 24 hours. One must not apply load on the anchor until the chemical has set completely.
Mechanical vs. Chemical Anchor Fasteners – Which one should you choose?
The fundamental differences between chemical and mechanical fasteners are listed below:
Speed: Load can only be applied to chemical fasteners once the chemical has set completely, whereas, a load can be applied on mechanical fasteners immediately upon installation. So, in case of speed-critical projects, it would be ideal to choose mechanical fasteners. However, there are quick-setting anchor epoxies (chemicals) on the market that take about 45 min to 1 hour to set, while regular epoxies take around 12-24 hours.
Waterproofing: Most mechanical anchors leave a slight gap between the fastener and the base material. In case of fastener installations outside the building like fixing an external AC unit, signage, or TV antenna, a mechanical fastener version may cause leakage into the building. In such a scenario, a chemical fastener is superior as the epoxy chemical fills up the recess between the bolt and base material, rendering a water-tight connection. Chemical fasteners are therefore suitable for external fastenings where leakage may be a pertinent factor.
Load Capacity: Regarding load capacity, it is not that one version of the fastener can bear more load than the other. Both the versions i.e. chemical and mechanical fasteners are available in a wide range of load ratings and capacities.
Of course, most anchors for use in safety-critical applications are specified by an engineer. As long as the engineer inputs the right data in the first place, the software will recommend a possible range of suitable products. Since they understand the difference between a mechanical and a chemical fastener, they can choose between alternative anchor fasteners type that is appropriate to the particular application.