What is UHPC?

What is UHPC

UHPC is a combination of binder and aggerate arranged and proportioned in a very specific way with a focus on particle packing. Ultra-High Performance Concrete is often referenced as extremely high performance concrete, ultra-high concrete, ductal concrete and always has excellent compressive, strength and durability. This concrete is extremely different from traditional concrete.

According to the FHWA, Ultra-High Performance Concrete is a cementitious composite material composed of an optimized gradation of granular constituents, a water-to-cementitious materials ratio less than 0.25, and a high percentage of discontinuous internal fiber reinforcement. The mechanical properties of UHPC include compressive strength greater than 21.7 kilopounds per square inch (ksi) (150 Megapascals (MPa)) and sustained post-cracking tensile strength greater than 0.72 ksi (5 MPa). Ultra-high performance concrete has a discontinuous pore structure that reduces liquid ingress, significantly enhancing durability compared to conventional and high-performance concretes.A handful of State departments of transportation have deployed UHPC components within their infrastructure, and many more are actively considering the use of UHPC. UHPC is a cementitious composite material composed of an optimized gradation of granular constituents, a water-to-cementitious materials ratio less than 0.25, and a high percentage of discontinuous internal fiber reinforcement.

A handful of State departments of transportation have deployed UHPC components within their infrastructure, and many more are actively considering the use of UHPC. UHPC is a cementitious composite material composed of an optimized gradation of granular constituents, a water-to-cementitious materials ratio less than 0.25, and a high percentage of discontinuous internal fiber reinforcement.

According to PCA

Ultra-High Performance Concrete

Ultra-High Performance Concrete (UHPC) is a cementitious, concrete material that has a minimum specified compressive strength of 17,000 pounds per square inch (120 MPa) with specified durability, tensile ductility and toughness requirements; fibers are generally included in the mixture to achieve specified requirements. Ultra-High Performance Concrete (UHPC), is also known as reactive powder concrete (RPC). The material is typically formulated by combining portland cement, supplementary cementitious materials, reactive powders, limestone and or quartz flour, fine sand, high-range water reducers, and water. The material can be formulated to provide compressive strengths in excess of 29,000 pounds per square inch (psi) (200 MPa). The use of fine materials for the matrix also provides a dense, smooth surface valued for its aesthetics and ability to closely transfer form details to the hardened surface. When combined with metal, synthetic or organic fibers it can achieve flexural strengths up to 7,000 psi (48 MPa) or greater.

Fiber types often used in UHPC include high carbon steel, PVA, Glass, Carbon or a combination of these types or others. The ductile behavior of this material is a first for concrete, with the capacity to deform and support flexural and tensile loads, even after initial cracking. The high compressive and tensile properties of UHPC also facilitate a high bond strength allowing shorter length of rebar embedment in applications such as closure pours between precast elements.

UHPC construction is simplified by eliminating the need for reinforcing steel in some applications and the materials high flow characteristics that make it self-compacting. The UHPC matrix is very dense and has a minimal disconnected pore structure resulting in low permeability (Chloride ion diffusion less than 0.02 x 10-12 m2/s. The material’s low permeability prevents the ingress of harmful materials such as chlorides which yields superior durability characteristics.

Some manufacturers have created just-add-water UHPC pre-mixed products that are making UHPC products more accessible. The American Society for Testing and Materials has established ASTM C1856/1856M Standard Practice for Fabricating and Testing Specimens of Ultra High Performance Concrete that relies on current ASTM test methods with modifications to make it suitable for UHPC. The following is an example of the range of material characteristics for UHPC:

Strength Compressive: 17,000 to 22,000 psi, (120 to 150 MPa) Flexural: 2200 to 3600 psi, (15 to 25 MPa)  Modulus of Elasticity: 6500 to 7300 ksi, (45 to 50 GPa)    Durability Freeze/thaw (after 300 cycles): 100% Salt-scaling (loss of residue): < 0.013 lb/ft3, (< 60 g/m2)  Abrasion (relative volume loss index): 1.7  Oxygen permeability: < 10-19 ft2, (<10-20 m2) 

Direct Tension test on Steelike UHPC
UHPC Direct Tension Test