Ultra high-performance fibre-reinforced concrete (UHPFRC) combines high strength concrete with steel fibres to increase the strength and durability of concrete. While there is much to be optimistic about regarding the use of this material in construction, research into UHPFRC is ongoing and will require further time to fully validate proposed industry uses.
Below, our own Andrew Young and Kevin Eisa, designers on our Bridge team, offer the key opportunities and challenges when working with UHPFRC.
Opportunities
1. Thinner, Lighter Structures: Since UHPFRC offers superior strength, less material is required than conventional concrete construction, resulting in the possibility of thinner and lighter structures.
2. Enhanced Durability: The UHPFRC matrix is very dense and effectively impermeable, resulting in low permeability and allowing minimal maintenance and a longer lifespan than conventional concrete.
3. Faster construction: Research into UHPFRC has often focused on prefabricated UHPFRC structural elements and this can allow for shorter construction time. These prefabricated elements can be built off-site and placed using UHPFRC closure pours on-site to significantly reduce construction time.
Challenges
1. Varying Strength: Tests of UHPFRC for structural applications show significant variation in tensile strength. This variation is an obstacle to being able to fully rely on the material’s tensile capacity.
2. Cost: While costs to produce and place UHPFRC have decreased in recent years, the presence of steel fibres and lower water-cement ratio compared to conventional concrete continues to result in a much higher cost of UHPFRC compared to conventional concrete.
3. Code Acceptance: While some codes, including the Canadian Highway Bridge Design Code (CHBDC), have started to include provisions to allow UHPFRC, code acceptance is ongoing and will take time. Where accepted in the CHBDC, most of a structure’s tensile capacity must still result from conventional reinforcement.
While UHPFRC offers new and interesting possibilities for design and rehabilitation, research is ongoing and will continue to focus on better quantifying structural capacity and developing innovative methods to use the material in a cost-effective manner.
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