Creep and Shrinkage of a Self-Compacting VHPC in Prebent Composite Beams for Innovative Railway Bridges in France-Part I: Modeling

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Title: Creep and Shrinkage of a Self-Compacting VHPC in Prebent Composite Beams for Innovative Railway Bridges in France-Part I: Modeling

Author(s): S. Staquet, C. Bouley, L. D’Aloia, R. Le Roy, B. Espion, and F. Toutlemonde

Publication: Special Publication

Volume: 246

Issue:

Appears on pages(s): 53-70

Keywords: creep recovery; shrinkage; very-high-performance concrete

Date: 9/1/2007

Abstract:
An extensive experimental study has been carried out to extend the Belgian technique of steel-concrete prebent beams to Very High Performance Concrete (VHPC: self-compacting C80/95 with silica fume). In comparison to the present constructions in Belgium, the main advantage of using VHPC instead of C50 concrete is to decrease the prestressing losses of the system thanks to a significant decrease of the creep deformations, together with the possibility to optimize the beam weight and its serviceability domain. As one research step was the casting of concrete around the bottom flange of two 13m-span steel girders, it was necessary to use a self compacting concrete with a suitable maximum aggregate size due to the very dense network of wires, sensors, ribbed stirrups and steel square ribs. In addition, the VHPC had to develop a very high compressive strength at early age to remove the prebending loads applied on the steel girders 48 hours after casting. The autogenous shrinkage development was examined both under standard isothermal (20°C) and realistic temperature (same as within the beams) conditions. Mechanical characterization, Young’s modulus, creep and shrinkage tests in standard (20°C, 50% RH) and variable (same as within the beams) ambient conditions were performed, so that a correct analysis of the structural behavior of the beams could be done. Due to the efforts of mixture proportions optimization, it could be demonstrated that VHPC delayed deformations were reduced by about a factor 2 in comparison with currently used C50 concrete, which made the use of prebending significantly more efficient. The purpose of this paper is to report on these experimental investigations and to present the computation method which was used to predict the time-dependent evolution of VHPC creep and shrinkage based on European model codes for the creep and shrinkage and on the recovery model proposed by Yue & Taerwe for the creep recovery.