Transition from Fluid to Solid Concrete in the Flexible Mould Process

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.Accepted Author ManuscriptConcrete StructuresApplied Mechanic

Self-compacting fibre-reinforced concrete

The project 'self-compacting fibre-reinforced concrete (SCFRC)' is part of the Dutch STW/PPM program - 'cement-bonded materials' - DCT.4010. Subproject III to which the project ,SCFRC' belongs deals with the development of new high performance concretes. The project 'SCFRC' aims at investigating the effect of type and content of fibres on the characteristics of self-compacting concrete in order to optimise the mixture composition. Fibres are able to bridge cracks and to improve the ductility of otherwise brittle cementitious materials. Therefore, the addition of fibres might extend the possible fields of application of self-compacting concrete. Besides the properties in the fresh state, while the concrete still flows, the mechanical behaviour will be investigated. This paper aims at introducing the reader to the goals, methods of research, and first experimental results of the project 'SCFRC'.Mechanics, Materials and StructuresCivil Engineering and Geoscience

Optimization of concrete for prefabrication and quantification of its environmental impact

The development of strength is an important criterion for the production ofprefabricated concrete elements. With seasonal changes of temperature that affect the development of concrete strength, daily cycles of often 18 hours or shorter have to bemaintained. The use of Ordinary Portland Cement (OPC) promotes high early age strength, but results in a relative high impact on the environment since cement production comes with decarbonation of components and a high energy demand. With the use of supplementary cementitious materials often comes a lower rate of strength development which might be compensated by one or more of the following measures: increase of cement fineness, curing at elevated temperature, optimization of the granular skeleton and/or use of accelerators.Steel & Composite Structure

Design considerations and sustainability of self-compacting concrete

Steel & Composite Structure

Strength development of concrete: balancing production requirements and ecological impact

The effective production of concrete structures requires adequate control ofstrength 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.Steel & Composite Structure

Rheological parameters used for deliberate deformation of a flexible mould after casting

This paper describes how curved precast concrete elements can be manufactured in an open and reusable flexible mould. The proposed method reduces formwork costs of architectural freeform elements in concrete. First, the method is described briefly, then a series of tests are discussed, demonstrating that by measuring the rheological parameters ofthe mixture during the process, the right moment of deformation con be determined. The measurements show that thixotropic behavior 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 the concretconcrete deformable in order to prevent cracking caused by the movement ofthe mould.Structural EngineeringCivil Engineering and Geoscience

Deliberate Deformation of Concrete in the Fresh State: Crack Risk and Efficient Production of Curved Precast Elements

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.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Steel & Composite StructuresMaterials and Environmen

Optimization of flowable concrete for structural design: Progress report of fib task group 8.8

With the tendency to apply concrete with a higher workability and the use of new concrete components more options are available to design concrete. New concrete types like self-compacting concrete (SCC), ultra-high performance fibre reinforced concrete (UHPFRC) and high performance fibre reinforced cementitious composite (HPFRCC) also require adopted mix designs and in case, a new engineering approach. Flowable concrete not only is an innovative material, but its application can lead to innovative structures, combinations of building materials and alternative and efficient production methods. fib Task Group 8.8 aims at facilitating the use of innovative flowable materials for the design of concrete structures and considers three aspects of flowable concrete for structural design: material properties, production effects and structural boundary conditions. The main objectives of this group of experts are to combine research findings with practical experience and to write a state of-the-art report and a recommendation on the structural design with flowable concrete. Areas of structural design where flowable concrete differs from traditional vibrated concrete have to be identified. This paper reports about the progress of fib TG 8.8 and discusses important aspects related to flowable concrete.Structural EngineeringCivil Engineering and Geoscience

Self-compacting fibre reinforced concrete applied in thin plates

Floor panels produced with traditionally vibrated concrete are relatively thick due to the need to reinforce concrete and consequently, heavy. Without the need to place rebars in panels and by applying self-compacting fibre reinforced concrete (SCFRC) the production process becomes more efficient. Fibres improve the performance of concrete by counteracting the crack-growth during loading. Their efficiency also epends on how they are distributed and oriented in a cementitious matrix. This paper describes a study on the application of thin plates with self-compacting concrete with and without fibres for floors; other materials like steel or wood often are applied for this application. Six concrete panels (dimensions: 600-600-15 mm3 ) were tested in this study; no rebars were placed in the elements. Self-compacting concrete was applied and the dosage of steel fibres was varied (0; 0,99 and 1,97 Vot.-%). The plates were tested by point-loading; the failure pattern depended on the fibre dosage.Structural EngineeringCivil Engineering and Geoscience

Shear behaviour of reinforced concrete beams strengthened with ultra-high performance fiber reinforced concrete (UHPFRC)

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.Concrete Structure