1. INTRODUCTION AND SCOPE
Throughout history, building materials have been reinforced with a variety of materials. In ancient times horsehair was used to reinforce mortar and straw was used to reinforce mudbricks. Moving into the 1900s, asbestos fibres found their way into concrete. The 1950s marked the emergence of composite materials, making fibre-reinforced concrete a significant area of exploration. In modern engineering, fibres of various materials like ceramics, plastics, cement, and gypsum products are used as fibres in plain concrete to improve composite features.

Lately, the construction industry is experiencing a growing trend – the use of steel fibre-reinforced concrete (SFRC) instead of traditional plain concrete for structural and non-structural concrete applications (Fig. 1.1). Multiple research studies have shown that SFRC has several benefits compared to traditional concrete such as increased tensile strength, higher resistance to crack opening, improved durability and improved resistances against fatigue, impact, and abrasion. Many of the available publications on this topic discuss the necessity to comprehend the performance of fastening systems in these specialised concretes.


Fig. 1.1: Different type of concrete reinforcement fibers (steel, white polypropylene etc.)

Today, Hilti brings you the first anchoring solutions approved for fastening in SFRC. The aim of this paper is threefold: to emphasise the importance of the growing trend to use this specialised concrete, to present an overview of the existing regulatory framework covering anchoring applications in SFRC, and to educate on the Hilti systems that are approved for use in SFRC: HAS-D with HIT-HY 200-A V3/-R V3, HUS4 in carbon steel and HST4. (HST4 is available from August 2025)

2. RELEVANCE OF THE TOPIC
To meet the growing demand for expanding applications, the EOTA Expert Group Fixings (EGF) has recently focused on incorporating steel fibre-reinforced concrete and the complete range of concrete strength classes defined in EN 1992-4:2018 [1] into the EADs. The latest updates for post-installed anchor qualification, such as EAD 330499-02-0601 [2] and variant EAD 330232-01-0601-v05 [3] introduce testing programs for anchor qualification in both normal weight concrete (C12/15 – C90/105, per EN 1992-4:2018) and steel fibre-reinforced concrete (SFRC; strength classes C20/25 to C50/60).

EAD 330499 [2] and EAD 330232 [3] adhere to the logic of normal weight concrete testing but include additional test series in SFRC to demonstrate equivalency, and a provision according to EN 14889 [4] which sets a maximum limit of 80 kg/m3 on the volume of steel fibres in the concrete.

For design purposes, a statement will be given in the relevant ETAs to allow following EN 1992-4 [1] regulations for anchors adequately qualified in SFRC. Static/quasi-static and seismic loading and performance in case of fire are already considered in EAD 330232 [3], while fatigue cyclic loading actions are currently not addressed in EOTA.

The option of a national-level qualification, such as through a general design approval in Germany ("Allgemeine Bauartgenehmigung"), remains available for conditions not regulated at European level, such as fatigue cyclic loading.

The new generation of Eurocode 2 (EN 1992-1-1:2023 ( [5])) addresses the design of steel fibre-reinforced concrete in a new informative annex. It is important to point out here that the new regulations for anchors in concrete only cover steel fibres and no other fibre types, nor a combination of steel fibres and other fibre types.

3. STEEL FIBRE REINFORCED CONCRETE
Plain unreinforced concrete has a low tensile strength and a low strain capacity at fracture. Concrete's fractile behaviour is enhanced by incorporating steel fibres into the mix. This transforms the brittle matrix of conventional concrete into a composite material, strengthened by randomly oriented, short, and discontinuous steel fibres with a specific geometry. The most significant properties of SFRC are the improved load-bearing behaviour, limitation of crack widths, improved shock and abrasion resistance, increased resistance to flaking and advanced notice of failure. Following crack initiation in SFRC, internal forces are efficiently transferred through fibres, optimising stress redistribution across the component cross-section (see Fig. 3.1and Fig. 3.2). These advantages mean that we see more and more SFRC relevant applications (e.g., industrial floors) which are subject to high loads and impact [6].

In addition, steel fibres may even replace standard bar reinforcement to a certain degree, since reinforcing with steel-fibres is a more productive process for casting large areas, e.g. in industrial floorings.

Fig. 3.1: Stress distribution in normal concrete [7] Fig. 3.2: Stress distribution in Steel fibre-reinforced concrete [7] 

3.1 Steel fibres
Steel fibres are commonly characterised by their shape, cross-section and length, aspect ratio, and tensile strength (Fig. 3.3). The aspect ratio, defined as the fibre length divided by the equivalent diameter of a fibre, influences the maximum volume of fibre per cubic meter of concrete. In concrete containing normal quantities of coarse aggregate, exceeding 1% steel fibre dose rate (approximately 80 kg/m3 ) is rare due to the interference and Stress-free crack Aggregate interlock Fiber bridging 2 / 6 impact on workability between the fibres and coarse aggregate. Typically, steel fibres account for 0.3% to 0.6% of the overall concrete volume (25 to 45 kg/m3 ), with higher doses used in specialised concrete with minimal coarse aggregate.

EN 14889-1 [4] classifies steel fibres into five groups. Group I fibres are the most widely used steel fibres:

• Group I: Cold-drawn wire
• Group II: Cut sheet
• Group III: Melt extracted
• Group IV: Shaved cold drawn wire
• Group V: Milled from blocks


Fig. 3.3: Example of steel l fibres

4. TYPICAL APPLICATIONS
In contemporary construction, conventional fibre-reinforced concrete (FRC), like SFRC, is extensively employed in industrial flooring. Its primary purposes include mitigating premature shrinkage cracks and enhancing resistance to impact loads or abrasion. Post-installed anchors are also applied in such settings, securing industrial components or heavy machinery. In fact, the crack bridging mechanism of fibres and the less brittle concrete breakout failure mode improve the load-bearing capacity of SFRC, making it an ideal base material to install anchors in concrete [6].


Fig. 4.1: Industrial flooring Fig. 4.2: Civil construction (pre-cast)

Approximately 60% of all new industrial floors are currently made using steel fibre concrete (Fig. 4.1). They are especially prevalent in places where concrete floors must withstand heavy mechanical loads, such as in high rack warehouses, production halls, or logistics centres.

Additionally, steel fibre-reinforced concrete is used in civil construction (Fig. 4.2). The use of steel fibres in a precast element factory can optimise processes considerably, with significant cost savings. Other SRFC applications may include fibres mixed into thin concrete elements, for example, in a residential sector, shotcrete applications and applications within a specialised construction.

Although steel fibres are used in tunnels, in some cases this application also contains a portion of polymer fibres to prevent spalling in case of fire.

5. HILTI ANCHORING SYSTEMS ASSESSED FOR SFRC
Post-installed anchors assessed for use in SFRC have valid ETAs and the approval clause is also added. Table 5.1 shows popular anchor solutions with diameter range, the relevant approvals and loading conditions for use in SFRC.



Table 5.1: Hilti anchors used in SFRC

Sample approval clause from ETA-21/0878 [8] valid for Hilti HST4 / HST4-R mechanical anchors shown in Fig. 5.1 is valid for the other anchors mentioned in Table 5.1 as well.

Fig. 5.1: Sample approval on SFRC from ETA-21/0878

6. DESIGN WITH PROFIS ENGINEERING
PROFIS Engineering software has included SFRC as a new base material for both uncracked and cracked concrete, which can be selected through a drop-down menu (Fig. 6.1). The approved anchors are shown in a list in the “Anchor” tab and user can select the suitable anchor from the list, when SFRC is selected as base material

Fig. 6.1: PROFIS Engineering covering SFRC The design report generated by PROFIS Engineering is also adjusted for the cases when steel fibre-reinforced concrete is used.

An example report is shown in Fig. 6.2.

Fig. 6.2: PROFIS Engineering report highlights the use of SFRC as a base material

7. SUMMARY
In conclusion, the historical evolution of building materials has led to the current trend of utilising steel fibre-reinforced concrete (SFRC) in construction and using this type of specialised concrete is becoming more and more common. SFRC offers several advantages over traditional concrete, including increased tensile strength and enhanced resistance to cracking, fatigue, impact, and abrasion. For these reasons, the use of SFRC in the construction business is steadily growing.
On the other hand, the lack of anchoring solutions with an ETA for fastening in SFRC has been a challenge for those applications which need to be designed according to Eurocode regulations.

Hilti solutions approved for use in SFRC with updated relevant ETAs can be designed as per EN 1992-4 [1] and using PROFIS Engineering software.

To start designing, visit https://profisengineering.hilti.com


8. REFERENCES
[1] EN 1992-4:2018: Eurocode 2 - Design of concrete structures - Part 4: Design of fastenings for use in concrete, Brussels: CEN, 2018.
[2] EOTA EAD 330499-02-0601: Bonded fasteners and bonded expansion fasteners for use in concrete, Brussels: EOTA, 2022.
[3] EOTA EAD 330232-01-0601: Mechanical fasteners for use in concrete, Brussels: EOTA, 2021.
[4] EN 14889-1 – 2007 – Fibres for concrete, Part 1: Steel fibres - Definitions, specifications and conformity, 2007.
[5] EN 1992-1-1:2023: Eurocode 2 - Design of concrete structures - Part 1-1: General rules and rules for buildings, bridges and civil engineering structures, Brussels: CEN, 2023.
[6] B. B. A. S. Mate Toth, Anchorage in steel fiber reinforced concrete – concept, experimental evidence and design recommendations for concrete cone and concrete edge breakout failure modes., Stuttgart: Institute of Construction Materials, University of Stuttgart, 2019.
[7] M. T. A. S. Boglarka Bokor, Influence of steel fiber content on the load-bearing capacity of anchorages in concrete., Stuttgart: 3rd international Symposium on Connections between steel and concrete., 2017.
[8] ETA-21/0878: HST4-R, HST4; Torque-controlled expansion anchor for use in concrete: sizes M8, M10, M12, M16 and M20, Marne-la-Vallée: CSTB, 31.10.2024. (HST-4 available August 2025)
[9] S2C Handbook: Steel to concrete connections using Post-installed systems, Schaan: Hilti Corporation, 2024.
[10] ETA-18/0972: Injection system Hilti HIT-HY 200-A, HIT-HY 200-R, HIT-HY 200-A V3 and HIT-HY 200-R V3 with HAS-D, Berlin: DIBt, 2023.
[11] ETA-20/0867: Hilti screw anchor HUS4. Mechanical fasteners for use in concrete, Berlin: DIBt, 2024.
[12] abG Z-21.3-2155: Injektionssystem Hilti HIT-HY 200 mit HAS-D zur Anwendung in Stahlfaserbeton unter ermüdungsrelevanter zyklischer Beanspruchung, Berlin: DIBt, 2024.