Ultra-High Performance Concrete (UHPC), also known as reactive powder concrete (RPC), is a high-strength, ductile material formulated by combining portland cement, silica fume, quartz flour, fine silica sand, high-range water reducer, water, and steel or organic fibers. The material provides compressive strengths up to 29,000 pounds per square inch (psi) and flexural strengths up to 7,000 psi.

The materials are usually supplied in a three-component premix: powders (portland cement, silica fume, quartz flour, and fine silica sand) pre-blended in bulk-bags; superplasticizers; and organic fibers. 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 use of this material for construction is simplified by the elimination of reinforcing steel and the ability of the material to be virtually self placing or dry cast.

The superior durability characteristics are due to a combination of fine powders selected for their grain size (maximum 600 micrometer) and chemical reactivity. The net effect is a maximum compactness and a small, disconnected pore structure.

The following is an example of the range of material characteristics for UHPC:

Strength
Compressive: 120 to 150 MPa (17,000 to 22,000 psi)
Flexural:15 to 25 MPa (2200 to 3600 psi)
Modulus of Elasticity: 45 to 50 GPa (6500 to 7300 ksi) 

Durability
Freeze/thaw (after 300 cycles): 100%
Salt-scaling (loss of residue): < 60 g/m2 (< 0.013 lb/ft3) Abrasion (relative volume loss index): 1.7 Oxygen permeability: <10-20 m2 (< 10-19 ft2) Cl - permeability (total load): < 10 C Carbonation depth: < 0.5 mm (< 0.02 in.)
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Figure 1. Shawnessy Light Rail Transit Station, Calgary, Canada

First Use of Ultra-High Performance Concrete for an Innovative Train Station Canopy

By V. H. Perry and D. Zakariasen, Lafarge Canada Inc.

The Shawnessy Light Rail Transit (LRT) Station, constructed during fall 2003 and winter 2004, forms part of a southern expansion to Calgary’s LRT system and is the world's first LRT system to be constructed with ultra-high performance concrete (UHPC). The innovative project, designed by Enzo Vicenzino of CPV Group Architects Ltd., is owned by the City of Calgary, managed by the Transportation Project Office (TPO), and constructed by general contractor, Walter Construction.

The Design

The station's 24 thin-shelled canopies, 16.7 feet by 19.7 feet, and just 0.79 inch thick, supported on single columns, protect commuters from the elements. Ultra-high performance concrete has a unique combination of superior technical characteristics including ductility, strength, and durability, while providing highly moldable products with a high quality surface aspect. The contract document specified a minimum requirement of 19,000 psi. In addition to the canopies, the components include struts, columns, beams, and gutters. The volume of material used totaled 105 cubic yards.

Manufacturing and Installation

The precast canopy components were individually cast and consist of half-shells, columns, tie beams, struts, and troughs. Table 1 summarizes test data from production of the twenty-four canopies.

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Figure 2. Half-canopy in steel form
  

The columns and half-shells were injection cast in closed steel forms (Figure 2). Troughs were cast through displacement molding, while struts and tie beams were produced using conventional gravity two-stage castings.

The columns were installed on the concrete platform first. Then, the right and left half-shells, along with the tie beams, were pre-assembled in the plant and transported to the site where they were lifted (by crane) over the railway tracks, for placement on the columns (Figure 3). Upon arrival at the site, the canopies were set on temporary scaffolding, and struts were attached to the shells and previously installed columns with welded connections.


Figure 3. Canopies ready for transportation   uhpc_Fig3

Conclusion

The material's unique combination of superior properties and design flexibility facilitated the architect's ability to create the attractive, off-white, curved canopies. Overall, this material offers solutions with advantages such as speed of construction, improved aesthetics, superior durability, and impermeability against corrosion, abrasion and impact—which translates to reduced maintenance and a longer life span for the structure. 


Iowa Boasts First Ultra-High Performance Concrete Highway Bridge in United States

uhpc01Iowa’s Wapello County boasts the first ultra-high performance concrete (UHPC) highway bridge in the United States, completed in May 2006. Although a simple, single-span bridge with a three-beam cross section, the Mars Hill Bridge is a significant step toward “The Bridge of the Future” – utilizing 110-feet UHPC girders that do not have any rebar for shear stirrups. The project was one of 96 presented at the 2006 Concrete Bridge Conference held in May in Reno, Nevada. 


References

Lafarge North America Inc. Ductal Website

Perry, V.H."Q&A: What Is Reactive Powder Concrete?" HPC Bridge Views, No. 16, July/August 2001.