Ultra-High Performance Concrete (UHPC), supplied by Hofmann 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.
Components
Fiber types often used in UHPC include high carbon steel, PVA, Glass, Carbon or a combination of these types or others. 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.
Compressive Strength
The UHPC 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.
Flexural Strength
When combined with metal fibers it can achieve flexural strengths up to 7,000 psi (48 MPa) or greater. 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 anchor embedment in applications such precast balconies or façade panels.
Construction
UHPC construction is simplified by eliminating the need for reinforcing steel in some applications and the material's 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.
Steel-Reinforced UHPC
Steel reinforced ultra-high performance concrete, in particular, stainless steel reinforced UHPC is the pinnacle of this innovative material group. It is achieved by randomly dispersed steel fibers achieving up to 2.5% vol. or discretely placed and staggered stainless or carbon steel mats achieving up to 10% vol. Both approaches are classified as UHFRC (fiber reinforced UHPC) and UHPMRC (mat reinforced UHPC).
Due to its high flexural capacity at minimal thickness, steel reinforced UHPC is ideally suited for façade/roof/soffit panels, louvers, lattice systems, and fins as well as other architectural elements such as balconies, stairs, etc.
Veneer-Faced Cladding
Stone, Brick, Terra-cotta, Ceramic, and even wood can be combined with thin ultra-high performance concrete elements to form precast veneer-faced cladding elements, which can span multiple floor heights. The integration of capillary mats allows the activation of the facade and roof elements for energy harvesting.
Worldwide Project References:
- World Trade Center Vehicular Security Center, New York
- WTC Liberty Park, New York
- Bronx 40th Precinct Police Station, New York
- WeWorkPark Avenue, New York
