High Performance Concretes in the Elorn Bridge


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Title: High Performance Concretes in the Elorn Bridge

Author(s): J. Le Bris, P. Redoulez, V. Augustin, J. M. Torrenti, and F. de Larrard

Publication: Special Publication

Volume: 140


Appears on pages(s): 73-94

Keywords: bridges (structures); cable supported structures; field tests; compressive strength; curing; field tests; heat of hydration; tests; high-performance concretes; high-strength concretes; lightweight concretes; loads (forces); quality control; stability; st

Date: 9/1/1993

The cable-stayed bridge which is being built across the Elorn river near Brest (western France) will have the world's longest span (400 m, or 437 yd) in this range of full concrete bridge. Besides a normal-strength concrete (C 35/6,500 psi), a lightweight concrete (LC 32/4,600 psi) is extensively used in the deck, in order to minimize the effect of dead load on the overall stability. But the most significant part of the loads to be carried by the bridge is due to the wind, with a maximum accounted speed (in the design) of 210 km/h (130 mph). Furthermore, the bridge is located about 3 km (2 miles) from the sea; thus, the wind will carry a large amount of chlorides. This is why the term serve environment seems to be appropriate for the Elorn bridge. Two grades of high-strength concrete--namely C60/ psi and C80/ psi--are used in the towers. For the first time in France--and perhaps in the world--a strength of 80 MPa (11,600 psi cylinder strength) has been used in the design of a bridge. Details on the concrete mix proportions, producing facilities, placing techniques and testing of samples are given in this paper. A special emphasis is put on the thermal curing aspects. As the thickness of the towers walls is 1.10 m (3.5 ft), the temperature can reach more than 80 C in the pylons. The effect of heat of hydration on the long-term strength and modulus was investigated. Also, finite-element calculations were performed, in order to predict the stresses induced by thermal gradients, and to choose the most appropriate curing (thermal insulation, time of form removal, and so on).