Compressive Strength
Ultra-High Performance Concrete (UHPC) represents a new class of concrete that has been developed since the 1990s. The inclusion of fibre in the composition offers enhanced strength characteristics that far exceed conventional concrete.
UHPC can exceed compressive strengths of 150-250 MPa. The use of micro and nano particles has a high impact on achieving these exceptional values. A low water to cement ratio is fundamental to the material's performance.
Flexural & Tensile Strength
UHPC is made with coarse, fine and micro fine aggregates combined with silica fume, producing a material with superior flexural and tensile properties compared to conventional concrete.
The fibre bridging effect across cracks is a key mechanism in UHPC's tensile performance. Various fibre types are used including PVA, steel, basalt, glass and carbon fibres, each contributing different characteristics to the composite matrix.
Fibre and Rebar Pull-Out (Bond Strength)
UHPC exhibits high bond strength due to its dense micro and macro-structures. The compact matrix creates exceptional adhesion between the fibres and the surrounding cementitious material.
Hooked and twisted fibres demonstrate significantly better pull-out resistance than straight fibres, providing enhanced structural integrity and load transfer capabilities.
Porosity and Permeability
UHPC has a remarkably fine pore structure with pore sizes less than 5nm and a pore volume of just 0.4-1.2%. This results in water absorption approximately 10 times less than High Performance Concrete (HPC) and 60 times less than Normal Strength Concrete (NSC).
The oxygen permeability of UHPC is approximately 1×10-19 m², making it virtually impermeable and highly resistant to environmental degradation.
Shrinkage and Creep
The creep coefficient for ordinary concrete can reach up to 3-4, whereas for UHPC it is less than 0.8. With heat treatment, this can be reduced further to less than 0.2, demonstrating exceptional dimensional stability under sustained load.
UHPC exhibits no drying shrinkage. Endogenous shrinkage is limited to 300-400 μm/m, significantly less than conventional concrete mixes.
Bending Behaviour
With approximately 2% metallic fibre content (equivalent to 50 million fibres per cubic metre), UHPC achieves a ductile bending performance that is fundamentally different from conventional concrete.
Under bending loads, micro-cracks are held closed by the fibre reinforcement, preventing crack propagation and maintaining structural integrity well beyond initial cracking.
Fatigue Behaviour
Under cyclic loading between 10-90% of the elastic limit, UHPC demonstrates excellent fatigue resistance. When loading remains below the endurance threshold, the material maintains its structural properties through millions of load cycles.
Behaviour under Fire
UHPC is classified M0 (non-flammable) and offers excellent resistance to fire exposure. Unlike conventional concrete, UHPC exhibits almost no spalling under fire conditions, maintaining structural integrity during and after fire events.
Mechanical Properties
| Property | Value |
|---|---|
| Compressive Strength | 120-250 MPa |
| Flexural Strength | 15-35 MPa |
| Water Absorption | <3.5% |
| Density | 2250 kg/m³ |
| Porosity | 1.5-6% |
| Poisson Coefficient | 0.2 |
| Coefficient of Thermal Expansion | 7.5-8.6 ×10-6 |
| Chloride Penetration | <100 coulombs |
| Carbon/Sulfates Penetration | None |