UHPFRC early age time dependent response - experimental characterization and numerical analysis

Eugen Brühwiler, Emmanuel Denarié, Aicha Kamen
Millpress, 2007
Article de conférence

Résumé

ABSTRACT: Thin ultra high performance fibre reinforced concretes overlays are suitable for rehabilitation of structures thanks to their enhanced properties. However, in such composite structures, restrained differential shrinkage cracking is an important concern. To investigate this problem a test set-up, inspired by previous research, was developed. The set-up simulates real restraint and thermal conditions commonly encountered in composite members. An analysis was first performed to identify the adapted configuration of the set-up from the point of view of geometry and cooling system, using a finite element program for time dependent behaviour of multilayer systems developed by (Femmasse 2007). The predicted temperatures and displacements are in reasonable concordance with measurements. The test results showed that the proposed set- up and the testing procedure are a practical and efficient approach for investigating the early age UHPFRC behaviour especially the evolution of the internal stresses, the autogenous shrinkage and the thermal effects.

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https://infoscience.epfl.ch/record/104204?ln=fr

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Thermo mechanical effects in Ultra-High Performance Fibre Reinforced Concretes (UHPFRC) at early age

Eugen Brühwiler, Emmanuel Denarié, Aicha Kamen, Hamid Sadouki

The extremely low permeability of Ultra-High Performance Fibre Reinforced Concretes (UHPFRC) associated to their outstanding mechanical properties make them especially suitable to locally "harden" reinforced concrete structures in critical zones subjected to an aggressive environment and to significant mechanical stresses. Composite UHPFRC-concrete structures promise a long-term durability which helps avoid multiple interventions on structures during their service life. Temperature Stress Testing Machines (TSTM) are very well suited to "experimentally simulate" the conditions encountered in composite structures in a new layer, at early age, subjected to restrained shrinkage under complex environmental conditions. They can also be used to determine intrinsic properties such as free shrinkage and creep response under well defined conditions of restraint and temperature. A new TSTM testing setup has been used to characterize the response of strain hardening UHPFRC, with different binders, under various thermo mechanical conditions. Isotherm tests as well as tests under realistic temperature conditions have been performed. Current numerical models have been applied to simulate the tests and the range of their applicability has been determined for temperatures between 10 and 30 °C. The test results showed a significant creep potential due to the high volume of paste. This beneficial effect was reflected by the linearly increasing-relationship between tensile creep and shrinkage. A Maxwell chain model was applied to predict the early age UHPFRC tensile creep at low stress levels. As expected, UHPFRC tensile creep behaviour was also sensitive to the stress level. Above 35 % of the tensile strength at the loading age of 3 days, the material exhibited a non linear behaviour.

2010

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The extremely low permeability of Ultra-High Performance Fibre Reinforced Concretes (UHPFRC)associated to their outstanding mechanical properties make them especially suitable to locally "harden" reinforced concrete structures in critical zones subjected to an aggressive environment and to significant mechanical stresses. Composite UHPFRC-concrete structures promise a long-term durability which helps avoid multiple interventions on structures during their service life. Temperature Stress Testing Machines (TSTM) are very well suited to "experimentally simulate" the conditions encountered in composite structures in a new layer, at early age, subjected to restrained shrinkage under complex environmental conditions. They can also be used to determine intrinsic properties such as free shrinkage and creep response under well defined conditions of restraint and temperature. A new TSTM testing setup has been used to characterize the response of two types of strain hardening UHPFRC, with different binders (CEM I and CEM III), under various thermo mechanical conditions. Isotherm tests as well as test under realistic temperature conditions have been performed. Current numerical models have been applied to simulate the tests and the range of their applicability has been determined for temperatures between 10 and 30 °C. Moreover, the significant influence of non linearity in the creep response of UHPFRC, at early age, under moderate to high tensile load levels has been demonstrated. The test results showed a significant creep potential due to the high volume of paste. This beneficial effect was reflected by the linearly increasing -relationship between tensile creep and shrinkage. As expected, UHPFRC tensile creep behaviour was also sensitive to the loading level. Above 35 % of the tensile strength at the loading age, the material exhibited a non linear behaviour. A Maxwell chain model was applied to predict the early age UHPFRC tensile creep and confirmed the observed non-linear response.

2008

Chargement

Thermo-mechanical response of UHPFRC at early age — Experimental study and numerical simulation

Eugen Brühwiler, Emmanuel Denarié, Aicha Kamen, Hamid Sadouki

The thermal effects on the Ultra High Performance Fiber Reinforced Concrete (UHPFRC) behavior are still not completely known. Under high temperatures, the processes that interact at early age are thermo-activated. All the experimental results obtained within this research confirmed it. Besides, certain authors observed a non-monotonous effect of temperature on the autogenous shrinkage and the creep of normal and high performance concretes. To clarify the thermal effect on the early age UHPFRC behavior an extensive experimental study was carried out. Tests results showed a non-monotonous effect of temperature on the autogenous shrinkage. In addition, finite element numerical simulations were performed to predict the experimental results and to validate existing models for different curing conditions. These models are necessary to predict accurately the deformations, the stresses and the damage (cracking) in the case of structural elements subjected to in-situ temperature variations.

2008

Chargement

, , ,

The extremely low permeability of Ultra-High Performance Fibre Reinforced Concretes (UHPFRC)associated to their outstanding mechanical properties make them especially suitable to locally "harden" reinforced concrete structures in critical zones subjected to an aggressive environment and to significant mechanical stresses. Composite UHPFRC-concrete structures promise a long-term durability which helps avoid multiple interventions on structures during their service life. Temperature Stress Testing Machines (TSTM) are very well suited to "experimentally simulate" the conditions encountered in composite structures in a new layer, at early age, subjected to restrained shrinkage under complex environmental conditions. They can also be used to determine intrinsic properties such as free shrinkage and creep response under well defined conditions of restraint and temperature. A new TSTM testing setup has been used to characterize the response of two types of strain hardening UHPFRC, with different binders (CEM I and CEM III), under various thermo mechanical conditions. Isotherm tests as well as test under realistic temperature conditions have been performed. Current numerical models have been applied to simulate the tests and the range of their applicability has been determined for temperatures between 10 and 30 °C. Moreover, the significant influence of non linearity in the creep response of UHPFRC, at early age, under moderate to high tensile load levels has been demonstrated. The test results showed a significant creep potential due to the high volume of paste. This beneficial effect was reflected by the linearly increasing -relationship between tensile creep and shrinkage. As expected, UHPFRC tensile creep behaviour was also sensitive to the loading level. Above 35 % of the tensile strength at the loading age, the material exhibited a non linear behaviour. A Maxwell chain model was applied to predict the early age UHPFRC tensile creep and confirmed the observed non-linear response.

2008