How to Improve Anchor Rod Performance

Why is hole prep so important?

An anchor rod will often fail pull testing due to an issue with the hole preparation and cleaning.

Allfasteners has been spending a significant amount of time in the field with contractors reviewing best practices for post installed anchor rods.

The first step in the process is drilling the hole in the tower foundation, a diamond core drill is the most common equipment for this. This type of coring creates a very smooth side wall which does not allow epoxy to bond well. The smooth, almost polished wall creates a need to mechanically roughen the cored holes to give more strength to bond between the concrete and epoxy.

The term “mechanically” roughen the hole has a very wide variety of definitions to the installer, with varied outcomes. Allfasteners quickly identified the need to create a standard for hole roughening which led to the development of our complete hole roughener kit. These come in different configurations based on hole diameter and depth. Common sizes range from 1.5” to 3” with 14’, 20’, and 30’ flexible shaft options. With this tool now as the standard for preparation, bond strengths of the epoxy have greatly increased. The hole roughener creates a surface more like a rock drill or SDS type bit.

Allfasteners has found that bond strength can rise up to 25% as a result of increased surface area. Once the holes are roughened they need to be flushed with water and brushed with the nylon brush included with the hole roughening kit. The roughened hole is flushed with water a second time, and compressed air is used to blow dry the holes. At this point, the holes should be dry and free of any loose material. A successful outcome is guaranteed when installers correctly use the AF35LVE epoxy and AF Hole Roughener.

The first step in the process is drilling the hole in the tower foundation, a diamond core drill is the most common equipment for this. This type of coring creates a very smooth side wall which does not allow epoxy to bond well. The smooth, almost polished wall creates a need to mechanically roughen the cored holes to give more strength to bond between the concrete and epoxy.

The term “mechanically” roughen the hole has a very wide variety of definitions to the installer, with varied outcomes. Allfasteners quickly identified the need to create a standard for hole roughening which led to the development of our complete hole roughener kit. These come in different configurations based on hole diameter and depth. Common sizes range from 1.5” to 3” with 14’, 20’, and 30’ flexible shaft options. With this tool now as the standard for preparation, bond strengths of the epoxy have greatly increased. The hole roughener creates a surface more like a rock drill or SDS type bit.

Allfasteners has found that bond strength can rise up to 25% as a result of increased surface area. Once the holes are roughened they need to be flushed with water and brushed with the nylon brush included with the hole roughening kit. The roughened hole is flushed with water a second time, and compressed air is used to blow dry the holes. At this point, the holes should be dry and free of any loose material. A successful outcome is guaranteed when installers correctly use the AF35LVE epoxy and AF Hole Roughener.

How much working time is needed?

The period of working time needed varies with the depth of hole and climatic conditions. Other commonly used epoxies have only 12 minutes of working time at higher temperatures; in many cases not long enough. Some contractors have tried refrigerating the epoxy to keep it from hardening as quickly; others have tried heating it up so the epoxy flows into the hole faster. Neither method has a reliable result, and the issue of working time still remains. AF35LVE has 22 minutes of working time, even when the base material temperature is as high as 100° F, allowing sufficient time to get the anchor installed even in the case of unforeseen site complications.

What happens if an anchor rod fails?

Anchor rod failure is serious and costly. It has been reported that the cost of a failed anchor rod could exceed $5,000. Failure can require purchasing replacement materials, remobilizing a crew to the jobsite, and additional testing is required on replacement anchor rods. Often, the new anchor must be rotated around the tower or the failed anchor rod must be extracted. Even all that additional time and money doesn’t guarantee a successful pull-test. 

Newly-approved AF35LVE epoxy has been specifically designed and tested for deep embedment anchor rods. To illustrate the obvious difference, Allfasteners compares the consistency or viscosity of other epoxies to peanut butter whereas the AF35LVE epoxy has a consistency similar to motor oil. To simplify installation, the anchor rod may be installed before the epoxy in most applications. The low viscosity will allow the material to flow around the anchor rod to the bottom of holes up to 20 feet deep.

Installers that use the AF35LVE epoxy and AF Hole Roughener, and utilize proper preparation methods, can have confidence that a successful pull test will be the result. We have tested and proven the integrity of this epoxy, and we guarantee that it will not fail when installed to our specifications.

For More Information, Contact Us

For more information regarding getting the most out of our products, contact a representative from the place For All Things Fastening, Allfasteners by calling 888.859.6060 or via email.