What Types of Fasteners are Used in Concrete?

When it comes to joining two objects together, choosing the correct fastener is crucial. Depending on the application and material being affixed, one must choose from the hundreds of fastener designs to find one that is compatible. In this blog, we will discuss the different types of fasteners that can be used when securing objects to concrete structures and what special considerations one must account for when dealing with this material.

Depending on its size and weight, a fastened object can be classified as structural or non-structural. An example of a non-structural item would be a picture frame or shelving, whereas a load-bearing wall would be considered a structural object. As such, the material and design of structural fasteners must be more durable than those supporting non-structural elements. However, some fastener designs can be used interchangeably.

Chemical fastening is a technique unique to concrete which involves drilling a hole into the material before filling it with a resin or epoxy. This resin will fill any gaps in the concrete and create a smooth, watertight adhesive surface to which the fastener can attach. This modality is beneficial because it allows the user to correct an oversized drill hole, fill any imperfections in the substrate, and protect the fastener from corrosion that may have otherwise occurred. However, improper resin application can degrade the fastener's ability to support heavier loads.

Mechanical fastening is the most straightforward method in concrete construction. This method involves the direct installation of a screw or anchor bolt into the concrete. Concrete screws work similarly to their wood counterpart, with the only difference being the need for a predrilled hole. Like any screw, they provide adequate tension and shear resistance, and because they are not designed to expand once applied, there is less chance of the concrete cracking. Alternatively, anchor bolts are explicitly designed for use in cracked concrete and can support heavier weights.

Expansion fastening is another technique implemented in concrete anchoring. Here, the fastener's base is designed to expand against the walls of the drilled hole, thus transferring the tension evenly throughout the concrete. While extremely effective when installed correctly, this method of fastening can destroy the underlying material if it is not sturdy enough to withstand the expansive force.

Determining the appropriate fastening technique for a given application depends on several factors. Primarily, one must consider the weight of the item they plan to mount. For example, an object like a metal door will require stronger and more frequently placed fasteners as compared to a picture frame. Additionally, one must consider the composition and rigidity of the substrate being used. As aforementioned, a thin or weak concrete base could easily be destroyed by an expansion fastener.

The installation process for concrete fasteners varies depending on the fastener type, but it is generally simple and can be done with few tools. For example, some mechanical fasteners are designed to be placed before the concrete has been set. This method saves time and slightly increases the anchoring strength, but is also permanent; thus, it necessitates proper placement. In contrast, post-installed fasteners require a hole to be drilled by a power drill with a masonry bit. When using this technique, it is important to use the correct sized hole and blow out any dust before installing the fastener.

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