Structural behaviour of hybrid elements with Advanced Cementitious Materials (HPFRCC)

Advanced Cementitious Materials such as HPFRCC are well adapted for durable repair and strengthening of concrete structures. Experimental and numerical investigations have been conducted to study the behavior of hybrid structural elements consisting of HPFRCC and ordinary concrete. The behavior at service state as well as at ultimate limit state of the beams reinforced with HPFRCC was comparable or better than the behavior of the beams reinforced with ordinary reinforced concrete. The sensitivity of numerical models for hardening materials such as HPFRCC was demonstrated

UHPFRC tensile creep at early age

Ultra high performance fibre reinforced concrete (UHPFRC) early age viscoelastic behaviour under tension was investigated. The tests results showed a high creep potential due to the high volume paste (88%). This result is of major importance because the viscoelastic properties contribute to mitigating the high early age stresses generated under restrained shrinkage. This beneficial effect was reflected by the increased linear-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 viscoplastic behaviour. A Maxwell chain model was applied to predict the early age UHPFRC tensile creep and confirms the induced non-linear respons

Evaluation of UHPFRC activation energy using empirical models

The influence of thermal curing on the evolution of the material properties and the UHPFRC behaviour was investigated. Tests results showed a beneficial effect of a high temperature curing on the early age material properties due to the thermo-activation effect on the hydration process. However, an inverse effect was observed at long-term. In our study, activation energy of UHPFRC was evaluated from experimental data by means of empirical models. The traditional maturity-function based on Arrhenius law, generally used to describe thermally activated physical or chemical processes, was used to predict the evolution of the UHPFRC autogenous shrinkage and to validate the applicability of this concept for such cement-based materials. Results showed that the concept based on Arrhenius law could describe correctly temperature effects on UHPFRC for temperature lower than 30°

Stahl-UHFB – Stahlbeton Verbundbauweise zur Verstärkung von bestehenden Stahlbetonbauteilen mit Ultra-Hochleistungs-Faserbeton (UHFB)

Die Grundidee der Stahl-UHFB – Stahlbeton Verbundbauweise besteht darin, mit einer UHFB Schicht, die in Haupttragrichtung mit Bewehrungsstäben versehen ist, Bauteile aus herkömmli- chem Stahlbeton zu verstärken, indem deren Tragfähigkeit er- höht und die Dauerhaftigkeit verbessert werden. Dadurch kön- nen die bekannten Schwachstellen und Mängel der Betonbau- weise eliminiert werden. Es wird ein Überblick über die Stahl- UHFB – Stahlbeton Verbundbauweise gegeben, indem die wesentlichen theoretischen Aspekte des Tragverhaltens von Stahl-UHFB – Stahlbeton Verbundbauteilen kurz erläutert und anhand von Anwendungen bei der Instandsetzung und Verstärkung bestehender Betonbauten illustriert werden. Schließlich werden Möglichkeiten des Einsatzes dieser neuartigen Bau- weise beim Bau von neuen Tragwerken aufgezeigt

Moisture Diffusivity of Fiber Reinforced Silica Fume Mortars

The moisture diffusivity is of considerable importance for quantitative assessments of creep and shrinkage as well as durability of cementitious material. For this reason, the influence of the composition of repair mortars on their effective moisture diffusivity as a function of the relative humidity of the surrounding air has been investigated. Silica fume, superplasticizer and polypropylene fibers have been added in order to reduce the permeability and to control cracking induced by drying shrinkage. It has been shown that the moisture transport in cementitious materials can be realistically described by a non-linear diffusion process governed by Fick's law. A computer program based on the finite volume method has been used in order to get the best effective moisture diffusivity by comparing experimental results (moisture losses of drying mortar cylinders) with the numerical solution. The applicability of a combined experimental-numerical approach to characterize repair mortars regarding their moisture diffusivity has been demonstrated. The material properties necessary for the characterization and qualification of new materials can be found numerically. Moreover, the diffusivities obtained provide useful input data for further numerical calculations. The positive effect of the addition of silica fume on the moisture diffusivity was clearly shown. The positive combined effect of polypropylene fibers and silica fume with increasing entrained air content was observed. Finally, no significant detrimental effect on the addition of fibers (even at relatively high volumes) has been observed for materials cast under shrinkage free conditions

Model for predicting the UHPFRC tensile hardening response

Ultra High Performances Fibre Reinforced Concretes (UHPFRC) are characterised by an ex-tremely low permeability and outstanding mechanical properties. These characteristics make UHPFRC suitable for locally “harden” reinforced concrete structures subjected to aggressive environments and/or mechanical stresses. Results from uni-axial tensile tests on different UHPFRC materials and cast in different directions have shown a variety of mechanical behav-iour. In particular, the hardening behaviour ranges from 0.1-0.4 % but is, in some cases, not existent. A meso-mechanical model is developed to predict the UHPFRC tensile response as a function of the volume, aspect-ratio, distribution and orientation of the fibres and the mechanical properties of the matrix. The model allows determining the effect of two parameters, the coeffi-cient of orientation and the volume of fibre, on the hardening behaviour

Evaluation of UHPFRC activation energy using empirical models

The influence of thermal curing on the evolution of the material properties and the UHPFRC behaviour was investigated. Tests results showed a beneficial effect of a high temperature curing on the early age material properties due to the thermo-activation effect on the hydration process. However, an inverse effect was observed at long-term. In our study, activation energy of UHPFRC was evaluated from experimental data by means of empirical models. The traditional maturity-function based on Arrhenius law, generally used to describe thermally activated physical or chemical processes, was used to predict the evolution of the UHPFRC autogenous shrinkage and to validate the applicability of this concept for such cement-based materials. Results showed that the concept based on Arrhenius law could describe correctly temperature effects on UHPFRC for temperature lower than 30A degrees C

UHPFRC tensile creep at early age

Ultra high performance fibre reinforced concrete (UHPFRC) early age viscoelastic behaviour under tension was investigated. The tests results showed a high creep potential due to the high volume paste (88%). This result is of major importance because the viscoelastic properties contribute to mitigating the high early age stresses generated under restrained shrinkage. This beneficial effect was reflected by the increased linear-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 viscoplastic behaviour. A Maxwell chain model was applied to predict the early age UHPFRC tensile creep and confirms the induced non-linear response