Combining the high strength of Ultra High Performance Concrete (UHPC) and the strain capacity of Strain Hardening Cementitious Composites (SHCC), Strain Hardening Ultra High Performance Fibre Reinforced Concrete (SH­UHPFRC) could be a promising material for the application of strengthening RC elements. This research describes the development of an SH­UHPFRC mixture, using Ultra High Molecular Weight Polyethylene (UHMWPE) fibres. The benefits of using this material as a strengthening material were analysed using a numerical model and the environmental impact of the SH­UHPFRC was evaluated. During the material development the effects of different material types and the applied ratios were considered. The flowability of the mixture, compressive strength and tensile response were tested to determine the mixture design. The effect of different cement types and amount of superplasticizer played a significant role in the increasing of the workability of the mixture. The effect of using UHMWPE fibres over steel fibres was investigated, as well as the effect the amount of UHMWPE fibres had on different properties. The material properties of the material research were implemented in a numerical model using ATENA software, representing a strengthened reinforced concrete (RC) beam subjected to a three­point bending test. In addition to the modelling of a RC beam strengthened with SH­UHPFRC, a parameter study was executed to determine the effect of increased strain capacity in the strengthening material. This was done by adjusting the tensile stress­strain relation in the material model. Three levels of strain were tested and the capacity and cracking behaviour of the strengthened beam were compared. The environmental impact was evaluated using the CUR Groen Beton calculation tool. The mixture design of SH­UHPFRC was compared to that of relevant concrete types. The environmental impact per volume is high for SH­UHPFRC, but the mechanical properties are superior which leads to a lower required volume to achieve similar mechanical results. Comparing a strengthened beam to a RC beam demonstrated the contribution of SH­UHPFRC, proving that, including the environmental impact, SH­UHPFRC could outperform NC as a strengthening material. The developed mixture granted a compressive strength of nearly 120 MPa, a tensile strength of 8.9 MPa and a tensile strain capacity over 2%. The use of this material for the strengthening of a RC beam lead to an increase in shear capacity of 78%, following from the numerical model. Evaluating the environmental impact, the use of SH­UHPFRC overcomes the use of NC to strengthen a shear­deficient beam. It is recommended to conduct further research on specific aspects of the material optimization of SH­UHPFRC. For the numerical modal the resemblance to practice could be improved and the range of parameters expanded. The environmental impact of a beam strengthened with SH­UHPFRC proved to be lower compared to an RC beam with equal shear capacity, showing the benefit of this superior material. An analysis of the full life cycle of an element strengthened with SH­UHPFRC could be done to get a better estimation of the environmental effect of using this material for strengthening purposes over NC.

Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) is, due to its superior mechanical properties and low permeability, a promising material for the restoration and improvement of the mechanical resistance and durability of existing Reinforced Concrete (RC) structures. This paper reviews the strengthening applications of UHPFRC in flexure, shear and punching shear, with a focus on shear performance of hybrid structures and the UHPFRC-concrete interface behavior which is governing the response of the hybrid beams. Holistic review approach is adopted considering not only structural behaviour of hybrid UHPFRC-concrete beams at the macro-scale, but also parameters governing the interface behaviour between concrete and UHPFRC at the meso- and micro-scale. Current analytical and numerical methods to predict the shear or punching shear capacity of RC structures strengthened with UHPFRC are reviewed and critically analyzed. Furthermore, the frequently overlooked role of interface, the effects of bonding technique, moisture exchange between the two materials, differential shrinkage and the role of coupled environmental and mechanical loads are discussed. It is observed that although extensive research work has been conducted to study the performance of hybrid UHPFRC-concrete structures, poor understanding of the behavior at the interface between concrete and UHPFRC, the role of thermal and hygral gradients and stress concentration for premature debonding, and the lack of reliable models and design codes impede the wide application of UHPFRC.@en

Digital fabrication with cementitious materials is a rapidly growing field of research in which the evolution of strength during the various processes, such as 3D printing, is the key controlling parameter. The strength evolves over multiple orders of magnitude during the process, and thus, it is essential to properly characterize the strength evolution in order to guarantee process success. This chapter summarizes the state of the art in these characterization methods for digital fabrication with fresh cementitious materials, reviewing well-known and more recently developed methods.@en

An investigation was executed into the applicability of self-compacting high performance fiber concrete in foundations. The applied concrete has a concrete cube strength of about 110 MPa and contains 60 kg/m³ hooked-end steel fibers (L_F = 30 mm, D_F = 0.38 mm). This publication consists of two parts: (1) Experimental assessment and verification of design rules and (2) assessment of fiber orientation and distribution. In the first part, experiments are described which were carried out to determine the pre- and post-cracking strength properties, the shear resistance of short beams, the anchorage length of rebars, and the shear capacity of foundation slabs supported on piles. The test results were used for a verification and extension of design rules for fiber reinforced concrete (FRC) found in the fib Model Code 2010. The application of the FRC developed can lead to substantial savings in concrete and reinforcing steel. In the present second part, cross-sections of two slabs and a beam of this testing series have been analyzed with regard to fiber orientation and distribution. An image analysis, executed on 111 concrete areas, indicates that a preferred fiber orientation could not be identified throughout the assessed elements. The data supports the conclusion of a good fiber distribution as well; a strong correlation was obtained for the data set of full images between measured and theoretical relation of fiber orientation and fiber density.@en

An investigation is carried out into the applicability of self-compacting high-performance fiber concrete (HPFC) in foundations. A concrete mixture has been designed with a concrete cube strength of about 110 MPa. The concrete contains 60 kg/m³ steel fibers. The properties of the HPFC developed are very suitable for structural applications, especially because the post-cracking tensile strength, provided by the fibers, is higher than the axial tensile strength of the concrete so that hardening in tension occurs after crack formation, often characterized by multiple cracking. This not only results in a high bearing capacity but as well in substantial durability. As a potential application foundation elements are considered. Experiments have been carried out to determine the pre- and post-cracking strength properties, the shear resistance of short beams with loads near to the supports, the anchorage length of reinforcing bars, and the shear capacity of pile caps. The results of the tests are used for verification of the applicability of the general design rules for fiber concrete, as found in the fib Model Code 2010, to the HPFC developed. The HPFC developed is characterized by high strength and ductility, is durable and self-compacting. The research program showed that the design of structures with the HPFC considered can be based on existing design rules with some extensions.

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Recent developments in concrete technology with high potential include ultra high performance concrete and self-compacting fibre reinforced concrete, which have a flowable consistency and can transport relatively high fibre dosages. Flowability is achieved by adopted mix design and both the mix design and flow affect the distribution and orientation of the fibres, which affect the post-cracking behaviour and accordingly the structural performance. With new materials also come new manufacturing and design approaches. The prediction of fibre orientation with computational fluid dynamics (CFD) simulations can be an important instrument to predict, understand and influence fibre orientation. With better understanding the mix design and casting process can be optimized.

This paper reports about a study executed to determine the applicability of the software package Autodesk Moldflow for fluid dynamics simulations of flowable fibre concrete. After a discussion of relevant literature, two reference cases address stretching and shearing flow conditions in a qualitative and quantitative way. Concrete was modelled as an incompressible Bingham material with addition of a fibre orientation model that was developed by Folgar and Tucker. A third case, a square panel, was used as a reference and structural element for flow simulations. Parameters varied were among others rotary diffusion, wall-slip and duration of casting.@en

Within the Dutch infrastructure there is the challenge of having to replace or strengthen a large number of existing structures within the upcoming years. This challenge also provides the opportunity to develop new concepts. The promising concept described in this report involves the application of UHPC to redesign the decks of existing concrete bridges in combination with the reuse of existing foundations. The Twentekanaal was selected as the topic of the project, because it comprises many bridges of which various have similar characteristics and were built in the same period. Not all bridges could be considered in-depth simultaneously. Therefore, one representative bridge was selected, the Eefdesebrug, after which the results for this bridge would be generalised onto all other relevant bridges across the canal. To determine the full potential of the project, it was investigated up to what extent the results for the Eefdesebrug could be projected onto other bridges across the canal. An inventory was set up containing all bridges. These were characterised and compared based on bridge category, year of construction and dimensions. This resulted in a total of twelve bridges with similar characteristics, to which the results of the redesign of the Eefdesebrug could potentially be generalised to. After the potential of the project had been determined, the focus was placed on the redesign of the Eefdesebrug, which was carried out following a stepwise approach. After each design phase, the global goal of the project was reflected by means of a weight comparison with the existing bridge. To limit the scope of the project, the new deck should be constructed using prefabricated beams. The design would be based on the Eurocode, supplemented by the AFGC-SETRA 2013 guideline. The final design resulted in a 32% reduction of the self-weight compared to the existing bridge. This design comprises pretensioned box beams with a slenderness of 36. A global assessment of the existing foundation was subsequently carried out. A criterion for reuse of the existing foundation was formulated based on the vertical loads due to permanent and vertical variable actions in the new and existing situation. This criterion was satisfied, with which the possibility of reuse of the foundation of the Eefdesebrug had been demonstrated. It was subsequently investigated what may be expected if the solution for the Eefdesebrug would be applied onto the group of twelve aforementioned bridges. Using the results for the Eefdesebrug it was possible to estimate the dimensions for the other bridges and to consider the vertical forces acting upon the foundations. It was shown that a similar solution can be applied to all twelve bridges across the Twentekanaal with characteristics similar to those of the Eefdesebrug.

The growing need for strengthening of concrete structures to improve their structural performance challenges structural engineers to come up with strengthening techniques that is most suitable and effective for a structural system in its deteriorated state. Although there are quite a few techniques in practice for strengthening of concrete structures -reinforced or prestressed, various factors limit their efficiency and performance. Use of novel concrete-based materials such as Ultra High Performance Fibre Reinforced Composite (UHPFRC) can lead to an effective strengthening system due to the exceptional material properties of UHPFRC. In particular, the strain hardening behavior of UHPFRC in tension and its excellent durability. Out of the two main mechanisms of failure in concrete elements namely flexure failure and shear failure, shear failure is the most critical due to the abrupt nature of its mechanisms that leads to complete collapse of the structures with no sign of warning. This makes shear strengthening of prestressed concrete structures, that typically form the supporting elements in large infrastructural units such as bridges, a very essential course of action. To investigate the effectiveness of using UHPFRC in shear strengthening of prestressed concrete elements, the post-tensioned T girders of Helperzoom bridge, Groningen, Netherlands are chosen as reference beams which are strengthened with UHPFRC. The reference beams are subjected to a 3-point bending test to determine their failure mechanism and structural capacity. The reference beam is modelled, and tests are simulated by finite element analysis using ATENA. Since the simulated beam failure in shear compression rather than shear tension by localization of the shear tension crack. In order to understand this behavior and the failure mechanism and to check if the results from the simulations are reasonable, a detailed analysis is performed. The influence of shear reinforcement and prestressing, active in the critical shear region, on the shear capacity and the final failure mode are investigated. The results from the numerical analysis are compared to the results from experimental shear tests performed on existing post-tensioned girders which exhibit a similar mode of failure as observed in the reference T beams. The shear capacity of the reference T beam is also calculated from the Flexural Shear Crack Model proposed by Huber et.al and it is seen that the shear capacity from the numerical analysis from ATENA is in close match to that obtained from the analytical model. The contribution of the arching effect to the shear capacity calculated from the model is between 77% and 87% for the beams tested in this research and the contribution is between 28% and 58% in the beams tested in the experiment. In the last step, the effectiveness of strengthening the reference beam with UHPFRC is determined. The results show that the effect of strengthening with UHPFRC is maximum in the reference beam without stirrups and prestressing both in terms of shear capacity and ductility.

The production of double-curved precast concrete elements for cladding or shell structures requires expensive CNC (computer numerical control)-milled formwork. As an alternative method, the innovative flexible mould for economically efficient and sustainable production of such elements is discussed in this paper. This method comprises the use of a flexible, CNC-controlled formwork, which is filled with self-compacting concrete. After a short period of thixotropic stabilization in the fresh state, the flexible mould is then deformed into its desired geometry, typically having a strong curvature radius of only a few metres in one or two direction(s). After hardening and de-moulding, the flexible mould can be reused for elements with the same or different curved geometry. The present paper describes the outcomes of a study focussing on two aspects relevant for the abovementioned production method: effect of change of rheological properties in the first 90 min after casting and assessment of the risk of cracking and development of cracks during the deformation process. In an experimental study the following parameters were modified: radius of deformation, moment of deformation in time, panel thickness and water-cement ratio. The presence of cracks after deformation was investigated quantitatively, using a petrographic technology. The results show that for the application of the flexible mould method the plastic stage of concrete is important to be considered.@en

The effective production of concrete structures requires adequate control of strength development in order to realise the scheduled production cycles. Demoulding of elements can take place only when sufficient strength is gained and the production cycle has to be maintained with seasonal changes of temperature. The use of Portland Cement promotes high early age strengths, but comes with a relative high impact on the environment since decarbonation and a high energy demand come along with cement production. Supplementary cementitious materials have been widely applied to improve the sustainability of concrete but the rate of early age strength development often is compromised to some degree.@en

Innovative structures can be designed with flowable concrete. A homogenous fibre distribution has to be assured by adequate mix design, whereas the fibre orientation depends on the flow and casting conditions, fibre length and rheological properties. Important work has been carried out during the past years on test methods and methods for non-destructive testing highlighting the necessity for on-site assessment of material behaviour of fibre concrete. The translation of results of small scale specimens tested in bending or in uniaxial tension is not necessarily straightforward and easy to execute considering a larger number of affecting parameters in the case of flowable concrete. This paper reviews the progress in understanding of how test results of small scale specimens relate to the structural behaviour of flowable fibre reinforced concrete. Results of recent studies reported in literature and carried out by members of fib Task Group 8.8 are considered.@en

Nachhaltiges Bauen ist ein wesentlicher Bestandteil des nachhaltigen und schonenden Umgangs mit der Umwelt. Da Beton bekannterweise der meist angewandte Baustoff weltweit ist, ist nachhaltiges Bauen mit Beton von groBer Bedeutung. Die Konzepte für die Planung, Qualitatssicherung und Bewertung beim nachhaltigen Bauen sind bereits sowohl auf der europaischen Ebene als auch landerspezifisch in Europa erarbeitet. Die Umsetzung dieser Konzepte befinden sich aktuell in unterschiedlichen Stadiën. Über das in den Niederlanden entwickelte Modell zur Bewertung der Nachhaltigkelt von Gebauden und die Erfahrungen aus den Niederlanden zum nachhaltigen Bauen mit Beton wird in dem Beitrag berichtet. @en

Advantages of concrete are freedom of shape, possibilities to integrate other functions and components, to build structures with limited maintenance costs, ease of use and very high durability. The use of sustainable building materials is important because they are used in large volumes. A significant reduction of the environmental impact can convince owners to select concrete instead of other building materials. Effective concrete production requires an adequate rate of strength development, which is especially important for prefabricated elements and ready-mix applications with a high early age strength requirement. This paper discusses the influence of the mix design on the global warming potential and the relative strength cost, the ratio between strength and environmental cost; 3 conventional vibrated concrete (CVC) mixtures and 9 self-compacting concretes (SCC’s) selected from literature are compared for the age of 24 hours and 28 days. Quantifying the trade-off between the use of Portland cement and other mixture components is important information to balance production requirements and to determine the environmental impact of concrete structures produced with SCC. @en