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Form Filling with Self-Compacting Concrete

Lars Nyholm Thrane

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Form Filling with Self-Compacting Concrete

The concept of self-compacting concrete was first introduced in Japan in the mid eighties and since then it has been subjected to much interest due to advantages that may be gained from the properties of self-compacting concrete with regard to quality, economics, working environment, and architectural degrees of freedom.

By definition, SCC is capable of flowing to every corner of the formwork influenced only by the concretes self-weight and casting technique while remaining stable (no blocking or segregation). Compared to traditional concrete, this may result in an improved concrete quality, because the homogeneity of traditional concrete is highly dependent on the vibration technique used, and most often, when using a poker vibrator, it varies according to the placement of the vibrator during the compaction process. Especially in confined zones, where manual vibration is difficult, the use of SCC may improve concrete quality.

The working environment and profitability may improve due to the elimination of health problems (white fingers, noise) derived from vibration, a shortened construction period, and a reduction in labour cost.

The development of SCC has contributed to an increasing degree of architectural freedom to carry out more complicated and advanced construction geometries, which may have been impossible to cast when using conventional concrete.

However, compared to traditional concrete it has proven much more difficult to control both the flowing properties and stability at the same time. It may be difficult to obtain a high flowability without segregation occurring. Therefore, it is important to put much effort in optimisation of the whole concrete composition from particle composition to water and superplastizicer concentrations.

Furthermore, no valid standards are available at the moment for the use of SCC, and in Denmark, for instance, ready mix self-compacting concrete is almost only used for floor applications.

An important tool in the ongoing industrialisation and automation of self-compacting concrete will be to be able to simulate form filling on the basis of the fresh concrete properties (rheological properties), form geometry, reinforcement configuration, and casting technique (the primary objective of this project) and to develop models to estimate the rheological properties and stability (the secondary objective of this project). Focus will be on vertical form filling situations.

In this project the fresh concrete properties are characterised by a continuum mechanical approach according to its rheological properties. Comparative studies of the form filling during actual castings and simulations by a commercial Computational Fluid Dynamics (CFD) program will be carried out to verify if a continuum mechanical approach is valid, and if the SCC can be characterised by the Bingham model or other parameters, such as thixopropic behaviour, have to be taken into account.

Investigations will be carried out to verify and further develop models based on the composite theory describing the effect of mixture composition on the rheological properties and stability of fresh SCC.

The project is carried out in co-operation between the Danish Technological Institute, Technical University of Denmark, and 4k-Beton A/S (ready mix concrete manufacturer).