There is a need to develop innovative repair materials which can overcome the challenges of cement-based repair mortars being relatively prone to shrinkage effects. In practice, free shrinkage of repair mortar is often considered as an indicator for potential cracking and delamination of applied repair mortars due to restrained shrinkage effects. As it is hard to measure restrained shrinkage directly, a restraint factor (R) can be used to correlate both. This study investigates the shrinkage characteristics of strain-hardening cementitious composites (SHCC), making use of polyvinyl-alcohol (PVA), high-density poly-ethylene (HDPE), or short glass fibres, for the repair and strengthening of existing concrete structures. Along with drying shrinkage and autogenous shrinkage, restrained shrinkage has been characterized with respect to the concrete substrate. Furthermore, pull-off tests were performed to assess the bond properties of these repair mortars. The results show around 65% higher autogenous shrinkage in high strength SHCC mixes while there was a decrease in drying shrinkage compared to the reference mix. In contradiction to what was initially expected, an increase in fibre content from 1.5 to 2.0 vol% resulted in a significant increase in autogenous shrinkage, especially in the high strength SHCC mixes. The restraint factor for all repair mortars was determined and was found to be in the range of 0.82–0.94. The pull-off tests showed an overall excellent bond behaviour of all studied mortars.

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Ultra-high performance fiber reinforced concrete (UHPFRC) is an advanced cementitious composite with high compressive strength and low permeability. Due to its excellent mechanical properties and superior durability, UHPFRC is considered promising for strengthening of the existing concrete bridges. In order to examine its strengthening efficiency for shear capacity, an experimental study is carried out on shear-deficient beams without stirrups. Strengthening method comprising precast UHPFRC laminates being glued with epoxy resin on two lateral sides of the reinforced concrete beams, is examined. To investigate the robustness of the system under severe exposure conditions, some beams are subjected to freeze-thaw (FT) cycles. Beams are tested to failure under three-point bending configuration. Test results show that for epoxy resin bonding, UHPFRC shear strengthening is a promising method to increase the load and deformational capacity, and to limit the crack openings. The load capacity is doubled, and the deformational capacity is increased by around 60%. After exposure to 30 FT cycles, the strengthening efficiency and fracture behaviour of UHPFRC composite beams seem not to be affected. It seems that the interfacial bond strength is sufficient to prevent premature debonding between UHPFRC and NC, which under combined action of environmental exposure (e.g. FT) and mechanical loading might become a challenge. Finally, a finite element model is developed to predict and understand the shear behaviour of the reference and strengthened beams. In general numerical results show good agreement with the experimental results in terms of failure pattern and peak load prediction once the perfect bond model is used for the interface between UHPFRC and NC. In order to better understand the role of governing parameters on the shear capacity of the composite member, parametric studies are conducted focusing on the role of varying UHPFRC softening behaviour and UHPFRC-concrete interface properties.

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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

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

The form freedom enabled by digital fabrication with concrete technologies provides advantages for a wide range of concrete based objects, from architectural to structural elements. The current chapter focuses on the specifics of structural design and engineering of DFC with emphasis on those technologies based on Additive Manufacturing with extrusion. Since it is a new and innovative way to build, a clear common approach to structural engineering has not yet been developed. As a result, this chapter aims to introduce the specific challenges of structural design and engineering with the additive manufacturing technology, providing an overview of structural typologies that have been developed (especially concerning the reinforcement strategies, including fibre reinforcement). Furthermore, the structural principles adopted in DFC and the codified approaches used in conventional reinforced concrete is compared, and putative structural testing procedures and validation methods for DFC are reported.@en

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

A high performance fibre concrete with a cylinder strength of about 80 MPa was developed and tested both under laboratory and site conditions. The post-cracking properties were determined in a series of three-point notched beam tests according to EN 14651. Subsequently, double punch tests on 150 mm cubes were carried out to verify whether such tests could be used for control of the properties of the concrete cast at site. It was shown that the same relations can be obtained by using simple conversion factors. Additionally, it was studied if it is possible to test round panels according to ASTM C1550-02 to verify the properties of the fibre concrete. Also here, it turned out that it is possible to derive simple conversion factors to relate the results of the round panel tests to those of the notched beam tests. The findings provide useful information for a practical quality assessment with regard to the execution of fibre reinforced concrete structures.@en

The fib Model Codes aim at integrating in a single document the relevant knowledge for the structural design with concrete. Fibre reinforced concrete is already integrated in fib Model Code 2010 (fib MC2010) as a general category of materials. The group of flowable concrete consists of clusters of different types of concrete among others Self-Compacting Concrete, Ultra High Performance Concrete and Strain-Hardening Cementitious Composites. Being highly flowable is the distinguishing characteristic, flowable concrete might contain or not contain fibres. Although the fibre contribution on the structural level can be assessed on short-term, the structural behaviour also depends on the behaviour of the fibres and the matrix in which they are embedded. fib Task Group 4.3 worked on identifying and characterising different types of flowable concrete and discusses in a fib bulletin the most relevant aspects with regard to mix design, manufacturing, material performance and structural behaviour of flowable concrete which can allow innovative applications to be developed and realised. This paper discusses recent developments with regard to flowable concrete in a broader perspective and addresses the progress with regard to standardisation.@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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Strain-hardening cementitious composites (SHCC) have a high tensile strength and display a remarkable strain-hardening behaviour. These unique characteristics make them an interesting choice for improving the strength and durability of new and existing structures. The tensile strain behaviour of SHCC is strongly influenced by its rheological properties as they determine the hardened state behaviour such as fibre-bridging strength and ultimately the degree of multiple cracking. The presence of fibres significantly affects the rheological performance of SHCC.

This study aimed at investigating the relationship between rheological characteristics of SHCC mortar before and after the addition of different fibres. Polyvinyl alcohol (PVA), high modulus polyethylene (HDPE) and glass fibres were added at three different contents in order to assess their effect on the workability of SHCC. Flow tests along with rheological assessment were conducted to evaluate the fresh state behaviour of SHCC. The addition of fibres reduced the flowability of mix, especially at high dosages. A modified fibre influence factor was developed to characterize different types of fibres and was related to the viscosity and yield stress of the mix.@en

Discrete fibres have been added to concrete to improve its performance. Besides the post-cracking strength also other performance aspects can be enhanced. Fibre Reinforced SCC (FRSCC) and less flowable fibre concretes form the general group of fibre concrete. FRSCC distinguishes itself from conventional vibrated concrete in three main dimensions: strength, fibre content and flowability, the last two aspects being a prerequisite for FRSCC.
This chapter starts with a definition of FRSCC, which is a broad group of different types of fibre-containing mixtures. After consideration of their influence on the characteristics in the fresh state by adequate mix design and appropriate execution FRSCC can be applied to produce outstanding concrete structures. The discussion includes a broader view on execution, potential applications, material properties, structural behaviour and durability performance.@en

The transition period between the mixing of concrete and the begin of setting increasingly receives attention, as special production processes can be developed with tailor-made fresh state characteristics. In this publication the two processes of 3D Concrete Printing (3DCP) and the production with the Flexible Mould Process (FMP) are discussed and compared. The FMP is a relatively new manufacturing method that was developed to allow the efficient production of curved thin concrete panels for cladding or structural use. The term ‘flexible’ refers to the deformation into the required curved shape of both the compliant mould surface and the fresh concrete contained by the mould shortly after casting. After that deformation, both the mould and the concrete are left for further hardening until demoulding is possible. The development of the 3DCP technique progresses fast, hereby new perspectives are gained with regard to mix design, production and structural performance. Sideway, test methods need to be developed or re-evaluated. The early age strength and strain capacity are important parameters for both processes, although they are not the same with regard to magnitude, period or time after mixing. Both processes can be executed within an open window and with specific boundary conditions only. This publication discusses and compares both processes. The implications of these recent findings are translated to practical aspects with regard to the production with the FMP.

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Most of the bridges and viaducts in the Netherlands were built in the sixties and seventies of the last century, and an increasing number of them will have to be replaced due to technical or functional reasons. The Netherlands is not an exception, many industrialized countries will face a similar replacement task in the near future. With the increased traffic intensities and the importance of mobility, the design and construction strategies for new bridges have to be different from that in the past. New methods need to ensure that traffic hindrance due to construction works and (future) maintenance activities are minimized. At the Delft University of Technology, a SMART bridge concept is being developed for fast and hindrance-free infrastructural replacement. The optimal advantage is achieved by utilizing innovative but proven technologies, and by bringing academic research into practice. A combination of recent innovations in construction technology, such as advanced cementitious materials (ACM), structural health monitoring (SHM) techniques, advanced design methods (ADM), and accelerated bridge construction (ABC) is being used. These innovations represent a step towards the next generation of infrastructure where fast construction, intelligent bridge design, sustainability, zero-energy, no/low maintenance, and aesthetics are key features@en

This paper investigates the influence of a plasticizing admixture on the pore structure refinement of alkali-activated concrete and paste mixtures and the consequently enhanced performance. Alkali-activated fly ash-slag concrete and paste are designed using a polycarboxylate-based admixture with different dosages. The pore structure and porosity are analyzed using mercury intrusion porosimetry (MIP). The workability, compressive strength, chloride migration resistance and electrical resistivity of alkali-activated fly ash-slag concrete and paste are determined. The results show that significantly improved workability and strength development are obtained at an increased admixture content. The admixture improves the gel polymerization product layer most likely around the GGBS particles, densifying the matrix. The 28-day Cl-migration coefficient of admixture (1–2 kg/m³) modified concrete is equal to the reference mixture, while at the highest admixture content the Cl-ingress is increased. At the later ages (91-days), the Cl-migration coefficients of all concretes, non- and admixture-containing samples, are comparable and low (about 2.6 × 10⁻¹² m²/s). The MIP analyses show a significant decrease of the total and effective capillary porosity over time at an increased admixture content. The relationships between the porosity and other properties are discussed, at varying admixture contents.

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During the production of ordinary Portland cement (OPC) clinker a lot of carbon dioxide (CO2) is emitted. To improve the sustainability of concrete production, many studies were carried out to evaluate alternative binders for OPC. The use of alkali-activated cementitious materials (AAMs) reduces the amount of Portland cement clinker and a larger volume of industrial by-products such as fly ash (FA) and blast furnace slag (BFS) can be applied. The combination of an aluminosilicate precursor and an alkali activator is characterised by a slower early age strength development compared to OPC. Thermal curing of the concrete is a successful technique to overcome this drawback. Although, thermal curing promotes the early age strength development of OPC-based concrete, the strength at 28 days often is relatively lower. In terms of environmental impact of AAMs, a significant reduction in production-related CO2-emissions is possible by replacing OPC by FA and/or BFS. With a relatively small activator dosage, it was found that the CO2-emissions can be decreased by up to 85% for AAMs compared to OPC-based mixtures. In this research, the effect of the mix design and curing temperature on the early age strength development and the environmental impact of AAMs was investigated.@en

Double-curved structures in general, and monolithic concrete shell structures more specifically, can transfer forces very efficiently. As a result, the thickness-to-span ratio can be very low, which, material-wise, can lead to a very economical design. However, the construction of shell structures is very labour-intensive and comes with high formwork costs and shells in modern building practice are rarely constructed. Concrete shell structures can be cast in-situ making use of temporary formwork and falsework, but they can be (partially) prefabricated as well, like the Palazzetto dello Sport in Rome. Although precasting is an effective technology for the repetitive production of concrete elements, for double-curved structures, having a large variety of shapes, the advantages of precasting seem to diminish quickly as a result of high formwork costs. Another disadvantage of precasting shell elements obviously seems to be the complexity of the required connections. For shell structures, the loss of stiffness of the connections might even lead to a crucial reduction of the buckling stability. A combination of both building methods, the prefabrication of the supportive structure and a finish with a cast in-situ layer, solves this before-mentioned issues and the advantages of both methods are combined: reduction of the complexity of the connections with an in-situ cast concrete layer and integration of the supportive structure in the design for a more cost-efficient erection. This paper describes the study of an innovative, partially precast, alternative solution for the construction of shell structures, and specifically addresses the influence of connections between precast elements on the overall shell behaviour. The Green Planet gas station along the A32 highway in The Netherlands was selected as a design case for such a building method.@en

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

Expensive CNC (computer numerical controlled)-milled formwork is required for the production of double-curved precast concrete elements for cladding or shell structures. The innovative flexible mould method for economically efficient and sustainable production of such elements, developed at Delft University of Technology, comprises the use of a flexible, CNC-controlled formwork, which is filled with self-compacting concrete (SCC). This paper describes how curved precast concrete elements can be manufactured in this open and reusable flexible mould. The proposed method reduces formwork costs of architectural freeform elements made with concrete. First, the method is described briefly, then tests are discussed, demonstrating that by measuring the rheological parameters of the concrete during the process, the right moment of deformation can be determined. The measurements show that thixotropic behaviour of concrete for this manufacturing method is very helpful, since it leads to a quick increase of the yield strength of the fresh concrete, but still leaves concrete deformable in order to prevent cracking caused by the deformation of the mould. The change of the rheological behaviour of concrete in the period between mixing and deformation of the mould was assessed; an additional study was executed in order to assess the integrity of the concrete after the deformation of the mould.@en