With expert Edgar Kälin, CEO of his namesake engineering firm
Summary
In this episode of Podcast Concretely, the Ultra-High-Performance Fiber-Reinforced Compound (UHPFRC)—is introduced as a material that is revolutionizing structural preservation. Edgar Kälin, managing director of his eponymous engineering firm, shares his extensive experience with the material and explains its technical properties, advantages, and applications. The discussion also touches on market acceptance and the challenges engineers face when working with this innovative material. Furthermore, the potential for wider adoption of UHPFRC, particularly in the restoration of aging structures, is explored. Finally, the episode emphasizes the need to convince engineers and building owners of the material’s significant benefits.
What is UHPFRC?
Ultra-High-Performance Fiber-Reinforced Compound (UHPFRC or often just UHPC), is revolutionizing the construction industry. With its exceptional properties, including high compressive strength, water impermeability, and extreme abrasion resistance, UHPFRC offers a sustainable alternative for the repair, reinforcement, and waterproofing of structures.
Obwohl UHPFRC oft mit Beton verglichen wird, unterscheidet er sich deutlich: Es handelt sich um einen Hochleistungsverbundstoff mit einem hohen Anteil an Stahlfasern, der speziell entwickelt wurde, um die Schwächen herkömmlicher Materialien zu überwinden. Mit über 500 Anwendungen allein in der Schweiz hat UHPFRC bereits bewiesen, dass es ein unverzichtbarer Bestandteil moderner Bauprojekte ist.
Technical Advantage of UHPFRC
UHPFRC combines a variety of outstanding properties, making it a preferred material in the construction industry:
- Extreme strength: A compressive strength of 120 to 150 N/mm² (compared to 30–35 N/mm² for conventional infrastructure concrete).
- Water impermeability: UHPFRC contains no capillary pores, and shrinkage cracks are prevented by the steel fibers. This eliminates the need for minimum reinforcement. As a result, UHPFRC is permanently waterproof—making it ideal for structures exposed to extreme weather conditions or other environmental stresses.
- Abrasion resistance: The robust surface allows for use without additional coatings or overlays.
- Resistance to contaminants: UHPFRC is resistant to chlorides, CO₂, and other chemical influences, effectively eliminating the risk of corrosion.
- Fire resistance: By adding polypropylene fibers, spalling during fires is prevented, making it suitable for structures with high fire safety requirements.
These advantages make UHPFRC ideal for demanding projects such as bridges, underground parking structures, or heritage-listed buildings.
Example Applications
UHPFRC offers versatile applications, from reinforcing existing structures to developing innovative composite constructions. Here are some examples:
- Reinforcement of Existing Structures: UHPFRC enables the strengthening of concrete slabs, columns, beams etc. without restricting the use of the structures. One example is the punching shear reinforcement of an underground parking slab, where the material was applied directly to the existing slab. In another project, UHPFRC was pumped directly into the ceiling from below to secure a weakened load-bearing structure.
- Heritage Bridges: A 110-year-old bridge in the Emmental region was reinforced with UHPFRC after being closed due to the risk of collapse. The restoration was not only significantly more cost-effective than a new construction but also avoided 80–90% of CO₂ emissions. UHPFRC allowed the bridge to retain its historical integrity while meeting modern traffic demands.
- UHPFRC-Wood Composite Structures: A notable highlight is the combination of UHPFRC with wood. Two heavy-load bridges in Switzerland were built using glued laminated timber beams topped with UHPFRC slabs. These slender constructions support loads of up to 40 tons and require no additional sealing or asphalt surfacing.
- Directly Drivable Surfaces: UHPFRC is also suitable for directly drivable road surfaces, eliminating the need for asphalt.
- Stairs: An innovative example is an 8 cm thin UHPFRC staircase, which impressed the client with its aesthetics and stability.
Sustainability and Cost Efficiency
Despite its higher material cost (approximately 20 times that of conventional concrete per cubic meter), UHPFRC stands out for its long-term cost efficiency:
Reduced Material Usage: Its high strength allows for slender constructions, requiring less material.
Avoidance of Demolition: Restoring existing structures with UHPFRC saves resources and benefits the environment.
Extended Lifespan: Thanks to its resistance to water and contaminants, UHPFRC remains low-maintenance for decades.
A sustainability comparison for a heritage bridge revealed that resource consumption was 99% lower compared to a new construction. Such figures highlight the advantages of UHPFRC for resource-efficient construction practices.
Challanges and Recommendations for Engineers
The application of UHPFRC requires a precise understanding of the material. Edgar Kälin, CEO of a Swiss engineering firm, emphasizes:
Training is essential: Workers need specialized training, as UHPFRC has a thick consistency and cannot be handled like conventional concrete.
Material adaptation per project: UHPFRC can be used in different consistencies, ranging from honey-like thickness to a more fluid state.
Support from experienced suppliers: The success of a project often depends on the expertise of material suppliers.
Kälin recommends that engineers start with smaller projects, such as waterproofing or reinforcement, to become familiar with the material’s properties.
In the future, UHPFRC could develop into a specialized field within civil engineering—similar to steel or timber construction today. It will not only make existing structures safer but also pave the way for new approaches to sustainable building.
Future of UHPFRC
UHPFRC will not replace concrete but will continue to gain importance as a highly specialized material for sustainable construction projects. Its potential is particularly significant in the rehabilitation of old bridges and structures from the 1960s and 1970s.
In the future, UHPFRC could evolve into a distinct specialty within civil engineering—similar to steel or timber construction today. It will not only enhance the safety of existing structures but also open new pathways for sustainable building practices.
Conclusion
UHPFRC is more than just a building material—it is a solution to the challenges of modern construction. Its unique properties and versatility make it an essential tool for engineers seeking sustainable and innovative solutions.
From the restoration of heritage bridges to new constructions, UHPFRC offers possibilities that conventional materials cannot match. For engineers ready to take the next step, UHPFRC presents an exciting and forward-looking opportunity.