Question:
What is Reactive Powder Concrete?
Answer:
Reactive Powder Concrete is a high strength ductile material formulated from a special combination of constituent materials. These materials include portland cement, silica fume, quartz flour, fine silica sand, high-range water-reducer, water, and steel or organic fibers. The technology of the material is covered by one of many patents in a range known as Ultra-High-Performance Concretes, all under the trademark—Ductal®.
This new family of materials has compressive strengths of 25,000 to 33,000 psi (170 to 230 MPa) and flexural strengths of 4000 to 7000 psi (30 to 50 MPa), depending on the type of fibers used. The ductile behavior of this material is a first for concrete. The material has a capacity to deform and support flexural and tensile loads, even after initial cracking. These performances are the result of improved micro-structural properties of the mineral matrix—especially toughness—and the control of the bond between the matrix and the fiber.
The durability properties are those of an impermeable material. There is almost no carbonation or penetration of chlorides and sulfates, and high resistance to acid attack. Resistance to abrasion is similar to that of rock. The superior durability characteristics are due to the low and disconnected pore structure, which is generated as a result of the use of a combination of fine powder materials (maximum grain size of 600 microns), selected for their relative grain size and chemical reactivity. The net effect is a maximum compactness and a small disconnected pore structure.
There is almost no shrinkage or creep, which makes the material very suitable for applications in prestressed concrete. The use of this material for construction is simplified through the elimination of reinforcing steel and the ability of the material to be virtually self-placing or dry-cast. It can be produced with customary industrial tools by casting, injection, or extrusion.
Due to the use of powder-like components and the fluidity, the material has the ability to replicate the macro- and microtexture of the formwork. The result is a final product that can have a full range of colors and textures with a high quality surface.
Applications with Ductal® use less materials; are lighter in weight; more elegant; easier, faster, and safer to construct; lower in maintenance; and have a longer life than conventional materials. This new technology is consistent with the construction trends and demands for reducing labor, materials, construction time, and environmental impact, while increasing safety, security, durability, and the service life.
The first bridge project using this material was a pedestrian bridge in Sherbrooke, Quebec, Canada, constructed in 1997. The bridge was manufactured in a precast operation in six segments each 33 feet (10 m) long, transported to the site, and post-tensioned together. The bridge is a 3-D space truss with a clear span of 198 ft (60 m) and a top deck 1.25 in. (30 mm) thick. Currently under construction in Seoul, Korea, is a pedestrian bridge with a clear span of 390 ft (120 m) and a structural depth of 3.6 ft (1.1 m) using a modified double bulb-tee with a deck thickness of 1.25 in. (30 mm). Several other bridge projects are presently under development in North America, Europe, Australia, and Asia.
Answer contributed by Vic Perry of Lafarge Group, France. He may be contacted at [email protected].