Ask HiltiAskLearnArticles
Ask Hilti

HILTI Kwik-X, A New Anchoring Technology

about 1 year ago

The First Innovation in Dual Action Screw Fastening Technology

anchor,productivity,Innovation,Dual-action

5.1K

Given the large variety of anchor systems available on the market today, designers or installation professionals may find it difficult to select the appropriate anchor for a specific application. Typically, for post-installed anchoring applications, the choice is between mechanical anchors or chemical anchors where the anchoring system is selected considering the design needs, jobsite application, and construction conditions.

Fig 1. Below provides common differences between mechanical and chemical anchors.

Fig 1: Characteristics of mechanical vs. chemical anchoring systems

In general, the benefit of mechanical anchors is the simplified installation process compared to chemical anchors. Additionally, mechanical anchors may be more economical than chemical anchors but are considered less flexible in design and installation due to limited diameters and limited embedment depths.

The benefit of chemical anchors is they yield higher loads and the anchoring system can often accommodate smaller edge and spacing distances (especially when compared to expansion anchors). However, the use of chemical anchors is considered more complex due to the influence of temperature and water, and the accessories needed for proper installation such as: need for a dispenser, cleaning effort etc.

Consequently, it can be said that there is a demand for an anchoring technology combining the benefits – as much as possible of both anchoring technologies – mechanical anchors, and chemical anchors.

The Hilti Kwik-X dual action anchor does just that with the combination of the KWIK HUS-EZ (KH-EZ) mechanical screw anchor with the Kwik HUS Capsule (KHC) containing a specialized two-part adhesive.

The dual action anchoring system employs a concrete screw with a hexagonal head in conjunction with a foil capsule filled with the constituent bonding materials of an injection system, see Fig 2.


Fig 2: Kwik-X dual action anchor

The KHC of the Kwik-X dual action system contains polymer resin, hardener, and aggregates in a defined mix ratio. The KHC is placed in a drilled hole produced by either a hammer drill or diamond core drill. The concrete screw is driven through the capsule using an impact drill specified in the manufacturers printed installation instructions (MPII). When driving the concrete screw into the hole the KHC is shredded but also compressed. The resin hardener and aggregate are mixed and fill the annular gap around the concrete screw as the thread cuts into the wall. Simultaneously cracks around the anchor are filled with resin, see Fig. 3.

The Kwik-X dual action fastener load transfer mechanism is based on mechanical interlock and friction. The adhesive from the KHC increases the area of the mechanical interlock of the threads as they cut into the surrounding borehole and as well as filling the annual space around the screw. Following the full cure of the adhesive there is friction interlock between the screw and the cured adhesive.


Fig 3: Threads cut by Hilti KH-EZ screw and Hilti Kwik-X dual action anchor (Hilti KH-EZ concrete screw with Hilti Kwik-HUS Capsule)

Understanding Kwik-X: the dual action fastener

To understand the dual action anchor and why this anchoring technology is combining the benefits of mechanical anchors and chemical anchors the following points are relevant:

If the adhesive would be completely removed, the residual anchoring system would be a pure concrete screw transferring the load by mechanical interlock via the threads cutting into the wall, see Fig. 4.


Fig 4: Separating the simultaneously acting load transfer mechanism

In general, screw anchors alone are not able to maximize the concrete capacity in tension since the leading screw threads that are inserted in the concrete wear down during the screw installation, especially in higher strength concrete. This leads to the effective embedment, hef, being less than the nominal embedment, hnom. The concrete capacity in tension for design purposes, for both ACI 318 Ch. 17 and CSA A23.3 Annex D, is based on hef. As seen in Fig. 4, now that the adhesive from the KHC is filling the annular gap between the concrete and KH-EZ screw it enhances the mechanical interlock of the screw and allows the Kwik-X system to realize the full concrete capacity and the designer can now use hef = hnom which can drastically increase the tension capacity of the Kwik-X. Fig. 5 shows how the increase in hef enhances the design capacity.


Fig 5: Increased effective embedment depth, hef, due to the KHC

Additionally, the conditions influencing the bond behavior are absorbed by the working mechanisms of the concrete screw. In the case of bonded anchors, these are borehole conditions like cleaned vs. uncleaned boreholes, drilling process (hammer drilling vs. diamond coring), temperature of the base material and the long-term behavior of the chemical anchor type. The qualification tests for the Hilti KWIK-X dual action anchor show that the dual action system is less influenced by the parameters that effect traditional bonded anchors systems. However, this is only true, if the combination of thread geometry and characteristics of the adhesives are balanced as provided with Hilti KWIK-X dual action anchor.
 
Compliance of Kwik-X for use in concrete

A safe anchorage requires not only detailed planning and design but also the consideration that the anchor system performs reliably under ordinary and adverse job-site conditions. In the US the performance and characteristics of a construction product may be evaluated based on the testing requirements included in an assessment criterion (AC) issued by the International Code Council Evaluation Services (ICC-ES).

The International Code Council Evaluation Services (ICC-ES) provides testing requirements and assessment criteria intended to verify the suitability of a system, to specify the admissible conditions of use (e.g., loading type, environmental exposure among others) and ultimately to determine the characteristics of performance (i.e., resistance of the anchor) which are needed for the design of a fastening point. The outcomes of the evaluation with all relevant parameters for the construction product are then published in an evaluation service report, as usually foreseen by the International Code Council Evaluation Service Report (ICC-ESR) or IAPMO Evaluation Report (ER).

The ICC-ES Acceptance Criteria for Post-Installed Adhesive Anchors in Concrete Elements (AC308) is the current criteria used to evaluate post-installed chemical anchors prior to receiving an ICC-ES ESR or IAPMO ER. In February 2022, AC308 was revised to permit the use of screw anchors with chemical anchors, provided the screw anchor has an existing evaluation report based on ICC-ES Acceptance Criteria for Mechanical Anchors in Concrete Elements (AC193). The Hilti KWIK-X dual action anchor is tested to the assessment criteria AC308 and has subsequently been issued ESR-5065 by ICC-ES. The test program determines the characteristics of the product for all the potential failure modes. The values are then provided in the evaluation report. The test program includes a baseline tension resistance of the anchor as well as several sensitivity and robustness tests to verify the mechanical response of the entire system. The test includes the assessment of the combined pull-out and concrete resistance and an evaluation of the sensitivities and durability of the bonding material. These tests are conducted with the condition of fastener diameter and embedment depth, that is identified having the largest contribution to performance from the bonding material.

Benefits of the Hilti Kwik-X dual action anchor screw fastener depending on the applications
 
The Hilti KWIK-X dual action anchor provides key design and installation advantages due to the following reasons:
(a)     Additional flexibility for anchoring in cold weather conditions. The Hilti KWIK-X dual action anchor offers an extended temperature range for installation compared to traditional injectable adhesive by allowing installations in temperature conditions ranging from
-17°F (-27°C) up to 104°F (40°C). (Additional cure time is needed for lower temperatures, refer to MPII)
(b)     KWIK-X offers designers flexibility for design changes or even anticipate for future design requirements with the ability to fully remove the anchor and re-install in the same borehole with no reduction in capacity per the MPII (only one removal and reinstallation is permitted).
(c)     For installers, using the KWIK-X dual action anchor means 30 second cure times in temperatures 41°F (5°C) and higher, no hole cleaning for proper installation, no torquing (beyond the use of impact wrench to install), or restrictions of drilling techniques.

KWIK-X brings key benefits to the following applications:

Hilti Kwik-X is most applicable for structural baseplate connections and equipment and machinery attachments in normal weight or lightweight cracked or uncracked concrete under static, quasi-static and seismic loading. The benefit of Kwik-X is the dual action function (micro-keying & adhesion) adapting the performance to the application requirements.

Fig 6: Hilti Kwik-X for secondary structural attachments, machinery, and equipment

Hilti KWIK-X dual action anchor may also be used in non-structural safety related applications. For example, the attachment of handrails, guardrails, roofs, and lightweight steel structures to new or existing structures. For such applications the Hilti Kwik-X fastening system provides you the possibility of designing with smaller edge and spacing distances while also providing installers an anchor that is easier and faster to install that is still completely removable, see Fig. 7.


Fig 7: Hilti Kwik-X may be removed and re-installed into the same borehole up to one time per the MPII. Removability and re-installation is not covered in the Kwik-X dual action anchor Evaluation Service Report (ICC-ESR 5065) 

Poor performance of fastenings for equipment and anchoring systems can contribute to damage and productivity loss. The dual action technology and removability of KWIK-X when changing the position of the equipment provides you the advantages of being more flexible against functional changes.
 
Summary

The new Hilti KWIK-X dual action anchor is the first of its kind post-installed anchor that combines the advantages of chemical anchors with the advantages of mechanical anchors.
Hilti KWIK-X brings a productive solution with its easy method of installation in conjunction with high-capacity performance helping meet the needs of both designers and contractors. It pushes the boundaries compared to traditional injectable adhesive technology by offering extended temperature range for installation down to -17°F (-27°C) for cold weather installations and offers flexibility to accommodate design changes by offering a removable and re-usable solution.
Hilti Kwik-X also supports contractors with a productive anchor solution that no longer requires them to deal with extended cure times in installations 41°F (5°C) or higher, has no cleaning or torquing requirements (beyond the use of impact wrench to install), and has no mandatory accessories or restrictions of drilling method.
 
The best of both worlds for designers and contractors
… brought to you by Hilti.
 

No comments yet

Be the first to comment on this article!