Didier Brazillier, BHP 2000 Project*
The first use of the term high performance concrete (HPC) in France goes back to 1983 and the building of a bridge at Melun under the impetus of LCPC and SETRA (Research Agency and Bridge Department of the French Highways Administration, respectively). This is not only of historical interest but is also highly significant in terms of the logic underlying the application of these types of concretes in France. Firstly, HPC relates to bridges rather than buildings. In France, there are few high-rise buildings and very little competition with steel construction in this sector. Secondly, bridge ownership or sponsorship, particularly in the highly developed public engineering practice, has played a leading role. This includes the initiation and support of a large-scale research and development program on HPC, gathering together a large number of players in the civil engineering sector to form BHP 2000, and the preparation of an official design code for concretes with characteristic strengths up to 11,600 psi (80 MPa). Finally, HPC’s improved properties of durability and rheology have always been exploited hand-in-hand with the mechanical properties. Hence the name “high performance concrete” as opposed to “high strength concrete.”
Since 1983, over one hundred bridges have been built with HPC. They may be characterized by three approaches that correspond to the reasons for selecting HPC.
Structural Approach
The structural approach is based on enhanced mechanical properties. This leads to a reduction in materials and more slender structures. A parametric study performed by BHP 2000 has identified that span lengths could be increased by about 10 percent for equivalent design loads with the use of concretes with characteristic strengths of 11,600 psi (80 MPa) instead of 5800 psi (40 MPa). And so, new architectural concepts can become reality. Among bridges that have been constructed and serve to illustrate this approach are the following:
- The cable-stayed bridges of Normandy, Le Pertuizet, L’Elorn, and recently Beaucaire-Tarascon, with a 656-ft (200-m) central span constructed with a ribbed slab 31 in. (800 mm) thick
- The cantilevered viaducts on the Southeast TGV line in Avignon and on the Lyon ring boulevard with a slenderness ratio of 25:1
- The arched bridges over the Rance and the Crozet Rivers near Grenoble with an opening of 459 ft (140 m) for the main arch, which is made up of two ribs 47 in. (1.20 m) wide with an average depth of 78 in. (2.0 m)
- The pylons of the Chavanon suspension bridge with a 984-ft (300-m) span
Construction Method Approach
The construction method approach is used to optimize construction cycles. This may involve high strength concrete at early ages to ensure rapid reuse of formwork and/or earlier prestressing. Placement of concrete in congested areas is also made easier by the rheology of HPC. Bridges based on this approach include the Ile de Ré bridge, which is 1.9 miles (3.0 km) long, includes 44,000 cu yd (34,000 cu m) of concrete, and was completed in 12 months. Le Corbusier viaduct in Lille and the bowstring bridge over the canal from the Marne to the Rhine rivers in Strasbourg are composite structures where HPC was used in prefabricated concrete slabs.
Maintenance Approach
The maintenance approach involves improved properties resulting from the highly closed microstructure of HPC leading to a lack of carbonation, slower diffusion of chlorides, and lower porosity. The maintenance approach is supported by the ongoing development of predictive computational models based on the actual characteristics of the materials and the environment surrounding the structure. Consequently, a contractual objective for a minimum service life is now possible using design rules and a material formulation model. French engineering firms were able to construct the Vasco da Gama Bridge in Lisbon with this performance and durability approach. The maintenance approach is of particular interest for small bridges, which are, by far, the most common and for which the potential benefits of reduced maintenance are greater.
Following construction of the experimental bridge at Joigny, the French Ministry of Development initiated the design of a range of standard bridges with the objective of improved durability. The first series has been constructed at Bourges, Angoulème, Sens, and Montpellier. These bridges have a simple design consisting of a principal rib and very thin transversely ribbed cantilevers either prefabricated or cast-in-place. They make it possible to illustrate the three approaches described above:
- Structural—a 40 percent decrease in concrete volume, resulting in a very thin bridge deck and lighter foundations
- Construction Method—a gain of one week on a conventional construction cycle for the roadway
- Maintenance—better protection of the reinforcement from corrosion; thereby, generating substantial savings in maintenance and extending the service life
At present, the use of a wide range of HPCs is becoming more accepted. For example, the future bridge over the Rhine at Strasbourg is a prestressed concrete box girder with a central span of 673 ft (205 m) using concrete with a characteristic strength of 10,000 psi (70 MPa). Also, the use of prefabricated components and high early-age strengths for cast-in-place concrete or prefabricated components is increasing.
Considerable spin-offs have also been observed on all types of conventional concrete while the way has now been opened for the construction of the first experimental bridge with a 21,700 psi (150 MPa) fibrous concrete deck in Valence to be completed at the end of 2000.
Further Information
The following publications contain further information about High Performance Concrete in France:
Malier, Y. et al., “High Performance Concrete – From Material to Structure,” Van Nostrand Reinhold Inc, New York, 1992.
Malier, Y. and De Larrard, F., “French Bridges in High-Performance Concrete,” Utilization of High-Strength Concrete, Symposium Proceedings, Lillehammer, Norway, June 1993. De Larrard, F., “High-Performance Concrete: From the Laboratory to Practical Utilization,” CONTECH ‘94, RILEM Seminar on Technology Transfer, Barcelona, November 1994.
Brazillier, D., Bar, P., Millan, A. L., De Larrard F., and Roi S., “Innovative Design of Small Highway Bridges in HPC,” Fourth International Symposium on the Utilization of High-Strength/High-Performance Concrete, Symposium Proceedings, Paris, France, May 1996, pp. 1447-1456.
Toutlemonde, F., Brazillier, D., and De Larrard, F., “Recent Advances in France in High Performance Concrete Technology,” SEWC ‘98, Structural Engineers World Congress,
San Francisco, 1998, Paper T 185-3.
Malier, Y., Brazillier, D., and Roi, S., “The Bridge of Joigny,” Concrete International, American Concrete Institute, Detroit, MI, May 1991, pp. 40-42.
Brazillier, D., Roi, S., Hagole, D., and Ferte J. C., “New Developments in Standard Bridge using HPC,” New Technologies In Structural Engineering, FIP, Lisbon, 1997, pp 131-138.
“The French Technology of Concrete,” XIIIth Symposium, FIP, Amsterdam, May 1988.