UHPFRC for the cast-in place reinforcement of offshore maritime signalization structures

[EN] Offshore lighthouses are a remarkable historical heritage often over 100 years old. The management of their aging is a challenge. The extremely low permeability of Ultra-HighPerformance Fiber Reinforced Concretes (UHPFRC), combined with their outstanding mechanical properties (robust tensile Strain Hardening (SH) for specific mixes) are particularly suitable for the reinforcement of this type of structures and more generally offshore maritime signalization structures. These structures under the influence of tides and weather, exposed to a very aggressive environment, have very limited access. As for existing bridges, SH-UHPFRC provide in this case a robust, effective, and very durable reinforcement solution, making it possible to simplify and reduce the duration of interventions. In this context, an existing turret at sea, on the south coast of Brittany, was reinforced by the application of a 60 mm UHPFRC hull, cast in place by helicopter in a formwork around the existing masonry structure. This application paves the way for the reinforcement with the same materials of lighthouses at sea exposed to extreme weathering conditions, such as "La Jument" nearby the island of Ushant (Brittany, France).Denarié, E. (2018). UHPFRC for the cast-in place reinforcement of offshore maritime signalization structures. En HAC 2018. V Congreso Iberoamericano de hormigón autocompactable y hormigones especiales. Editorial Universitat Politècnica de València. 17-30. https://doi.org/10.4995/HAC2018.2018.8261OCS173

ARCHE D06 - Recommendations for the tailoring of UHPFRC recipes for rehabilitation

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. UHPFRC provide a unique and robust solution to simplify the construction process, dramatically reduce the duration of sites, and save money with long term durability. Rehabilitations, especially with cast on site UHPFRC are among the most demanding applications for those materials and require a significant strain hardening response under tension. Achievement of tensile strain hardening, extremely low permeability and self-compacting character is indeed a challenge that few current UHPFRC recipes can satisfy. Cement-superplasticisers compatibility issues severely restrict the range of possibilities to develop new UHPFRC recipes based on locally available components with the required properties for cast in situ applications. An original concept of Ultra High Performance matrix has been developed that makes the application of UHPFRC technology feasible with a wide range of cements and superplasticisers, with outstanding mechanical and protective performance, without significant loss of workability. This concept is an extension to UHPFRC materials of the concepts of cements blended with Limestone fillers, already applied successfully to a wide range of normal or high performance concretes. In a further step, the rheology of those mixes has been adapted to enable them to support challenging 5 % slopes of the substrates at fresh state. The development of this new technology and its portability in various countries opens very promising perspectives for the dissemination of this concept not only for rehabilitation but also for various applications of UHPFRC, prefabricated or cast-in-situ. This document presents both a general methodology for the tailoring of UHPFRC recipes (fibrous mix and matrix) and its application to Slovene and Polish components

SAMARIS D25b - Guidance for the use of UHPFRC for rehabilitation of concrete highway structures

order to manage structures effectively and to reduce this burden to the minimum, the number and extent of interventions have to be kept to the lowest possible level. The extremely low permeability of Ultra-High Performance Fibre Reinforced Concretes (UHPFRC) associated with 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. UHPFRC materials can be applied on new structures, or on existing ones for reha-bilitation, as thin watertight overlays in replacement of waterproofing membranes, as rein-forcement layers combined with reinforcement bars, or as prefabricated elements such as kerbs. This document gives an overview of the conceptual approach, and provides basic guid-ance in view of the application of UHPFRC for the rehabilitation of reinforced concrete structures

Essais de caractérisation - réponse en traction

Le comportement en traction des BFUP (résistance élevée et déformabilité notable) est un de leurs principaux attraits. Pour valoriser au mieux ces propriétés, il importe de disposer d’essais et de méthode d’analyse inverse permettant de déterminer la réponse en traction des BFUP soit directement au moyen d’essais de traction uniaxiale, soit indirectement au moyen d’essais de flexion sur bandes minces. Dans un premier temps on présente les deux types d’essais proposés pour caractériser la réponse en traction des BFUP : traction uniaxiale sur éprouvettes cintrées non entaillées et flexion 4 points sur bandes non entaillées et les paramètres qui en sont extraits. Dans un deuxième temps on illustre l’analyse des résultats d’essais au moyen d’exemples d’application basés sur le cas de chantiers récents

SAMARIS D22 - Full scale application of UHPFRC for the rehabilitation of bridges – from the lab to the field

The premature deterioration of reinforced concrete structures is a heavy burden for society. In order to manage structures effectively and to reduce this burden to the minimum, the number and extent of interventions have to be kept to the lowest possible level. The extremely low permeability of Ultra-High Performance Fibre Reinforced Concretes (UHPFRC) associated with 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. UHPFRC materials can be applied on new structures, or on existing ones for rehabilitation, as thin watertight overlays in replacement of waterproofing membranes, as reinforcement layers combined with reinforcement bars, or as prefabricated elements such as kerbs. This document gives an overview of the conceptual approach, and provides detailed informations on the first application performed during the European project SAMARIS (Sustainable and Advanced MAterials for Road InfraStructures), in view of the application of UHPFRC for the rehabilitation of reinforced concrete structures

Etude expérimentale des couplages viscoélasticité-croissance des fissures dans les bétons de ciment

Viscoelasticity and crack growth govern the long-term deformability of concrete and thus its service behaviour and its durability. For low load levels, viscoelasticity behaves quasilinearly and crack growth is inactive. On the other hand, for high load levels, cracks grow and interact with viscoelasticity. Numerous authors have long demonstrated the influence of microcracking on creep qualitatively. Moreover, rate effects on the fracture behaviour of concrete are clear for low and high loading rates. Nevertheless, the mechanisms involved in these effects are not yet clearly determined. Cohesive crack approaches extended to time dependent parameters, give some elements of explanation, although without providing a general tool capable of explaining all the phenomena. The dissipative nature of crack growth and viscoelasticity naturally encourages one to model their couplings by means of an energybased approach to fracture. This is the meaning of the continuum thermodynamics of dissipative multicracked granular bodies developed by Huet (1997). This theoretical formalism puts the emphasis on the effect of viscoelasticity on the driving (reactive) part of the propagation criteria (energy release rate). The aim of this experimental research was to investigate coupling effects between viscoelasticity and crack growth in concrete. With this aim in view, 4 different types of fracture test have been performed on the same material (concrete with a maximum aggregate size of 8 mm), with a constant specimen geometry (rectangular wedge splitting specimens 20 by 20 by 10 cm). The first type of test consisted of performing a series of successive relaxations, at various increasing load levels, before, on and after the peak force, following the envelope of failure. Special attention was devoted to the influence of the control parameter ("active": with respect to displacements measured on the specimen, or "passive": crosshead displacement) and loading history. The results showed a progressive deviation from the linear viscoelastic behaviour starting from a load level of approximately 50 % of the peak force, before the peak. This deviation was significantly higher with crosshead control ("passive"). It depended on the loading history. After the peak, in "active" displacement control, relative relaxations tended to be similar whatever the load level. The displacement parameters (other than control) measured on the specimen or crosshead during relaxation, showed an evolution dependent on the control parameter. This effect was significant at the beginning of the relaxation and tended to disappear later. Furthermore, acoustic emissions could be detected at the beginning and during some relaxations, for high load levels (nearby peak force and after). The second type of test consisted of one or more successive creep levels up to eventual failure under sustained force. In certain cases, during creep levels leading to fracture, alternating secondary and tertiary creep with multiple concavity changes correlated with measured acoustic emissions could be observed. The tertiary creep leading to fracture developed over several minutes. Unstable sudden crack propagation was only seen at the end of the tertiary creep levels, accompanied by a sudden and very fast increase of the number of acoustic emissions. Moreover, during tertiary creep, an increase of the crack length measured on the specimen's surface by means of a conductive crack graphite gauge could be observed, correlated with the evolution of the creep displacements. The third type of test was performed under constant displacement speed (displacement measured on the specimen in the axis of the splitting force) with a range of speeds from 5 x 10-4 to 5 x 10-1 mm/minute. The results show a clear influence of the displacement speed on the response in terms of force-displacement curve, in the vicinity of the peak. The maximum force decreases with the displacement speed. On the other hand, the displacement at peak force was not significantly influenced by the displacement speed. Surface crack length measurements by means of a conductive graphite gauge enabled the determination of the surface crack speed as a function of the imposed displacement. The obtained surface crack speed depended quasi linearly on the imposed displacement speed. The fourth type of test, complementary to the former ones, was especially for the study of the evolution of internal micromechanical parameters during crack growth. Two wedge splitting specimens were equipped internally, near to the potential crack path with optical strain gauges (Bragg gratings). The internal strain measurements, revealed two zones of very different behaviour, with similar tends for the two specimens. Optical strain gauges close to the fracture plane (less than 5 mm from gauge axis) measured high strains (around 1000 με) significantly greater than the ultimate tensile strain of normal concrete (0.1‰ or 100 με) and mostly irreversible. At the contrary, optical strain gauges farther from the fracture plane (over 10 to 15 mm) measured strains that were always smaller than 100 με , and mostly reversible. Finally, two types of computer simulation (homogeneous materials) were performed in order to complement the interpretation of experimental results. A linear viscoelastic calculation, for a constant crack pattern, was used to illustrate quantitatively the progressive deviation from linearity observed in the experimental successive relaxations. A non-linear calculation of the propagation of a discrete crack with softening behaviour, in a linear elastic material, accurately predicted some of the strains measured with optical strain gauges during crack propagation. The experimental results demonstrated many indications of crack growth activity during creep as well as relaxation levels. These measurements confirm the significant contribution of propagation and coalescence of microcracks to the non-linear viscoelastic response of concrete. Indications of microcrack growth during relaxation can be explained by unstable propagation phenomena triggered by the small size of the microcracks. These phenomena could be amplified by viscoelastic effects of the redistribution of internal stresses in the heterogeneous structure of concrete. All the work performed clearly shows the need to complement macroscopic measurements such as the reaction force of a specimen or external displacements, with the measurement of micromechanical parameters in order to distinguish the contributions of the different active phenomena and of their coupling

SAMARIS D13 - Report on preliminary studies for the use of HPFRCC for the rehabilitation of road infrastructure components

The aims of the preliminary study reported in this document were twofold. Firstly, within the context of the application of UHPFRC for the rehabilitation of reinforced concrete structures, to identify the phenomena that require further study with respect to the risk of delamination, transverse cracking and overall performance of the new layer and of the composite structural elements with UHPFRC. Secondly, on the basis of a state of the art, of experimental tests and numerical simulations, to select the UHPFRC materials that will be used in the main test series on the basis of their performance with respect to the processing (mixing, casting) as well as in the hardened state, for protection or reinforcement

SAMARIS D26 - Modelling of UHPFRC in composite structures

The extremely low permeability of Ultra-High Performance Fibre Reinforced Concretes (UHPFRC) associated with 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. UHPFRC materials can be applied on new structures, or on existing ones for rehabilitation, as thin watertight overlays in replacement of waterproofing membranes, as reinforcement layers combined with reinforcement bars, or as prefabricated elements such as kerbs. The successful rehabilitation of existing structures is a major challenge for civil engineers. When existing concrete needs to be replaced, a new composite structure formed of the new material cast on the existing substrate will result from the intervention. Both the protective function and the mechanical performance of the composite system have to be guaranteed over the planned service life. These requirements can be fulfilled by a sound understanding of the origin of deteriorations, and by proper design and application. Further, to take the full benefit of the potential of UHPFRC to rehabilitate or reinforce structures, it is often needed to get better insights of the performance of composite UHPFRC-Concrete members by means of numerical models such as finite element simulations. The numerical modelling of multiple layer systems involves comprehensive models of the time dependent behaviour of the materials at early-age and long term. UHPFRC require special consideration of their tensile hardening behaviour. This document gives the theoretical background, and provides validations of a constitutive model for UHPFRC under tensile loading. This model is then applied to the inverse analysis of test results in bending, and to the simulation of various configurations of application of UHPFRC in composite structural members

Next generation UHPFRC for sustainable structural applications

Over the last few decades, ever-increasing demands of society to the built environment have continually increased consumption of energy and materials for the construction and maintenance of structures. Meanwhile, Strain Hardening Ultra High-Performance Fiber Reinforced Concrete (SH-UHPFRC) have the potential to be one of the solutions to contain the explosion of maintenance costs (Economy and Environment), considering their extremely low permeability associated to outstanding mechanical properties and load bearing efficiency compared to deadweight. The objective of this research is to further improve the already established concept of UHPFRC application for rehabilitation. This paper reports firstly on the development and validation of new low Embodied Energy (EE) SH-UHPFRC mixes with 50 % clinker replacement by Supplementary Cementitious Materials and replacement of steel fibers by ultra-high molecular weight polyethylene (UHMW-PE) ones. In a second step, the mechanical and protective properties of the mixes are investigated with a special emphasis on their quasi-static tensile response, and transport properties. Finally, the dramatic improvement in terms of reduction of EE and deadweight of the proposed mixes is demonstrated