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This thesis addresses numerical simulations of self-compacting concrete (SCC) castings and suggests a novel modelling approach that treats reinforcement zones in a formwork as porous media.
As a relatively new field in concrete technology, numerical simulations of fresh concrete flow can be a promising aid to optimise casting processes and to avoid on-site casting incidents by predicting the flow behaviour of concrete during the casting process. The simulations of fresh concrete flow generally involve complex mathematical modelling and time-consuming computations. In case of a casting prediction, the simulation time is additionally significantly increased because each reinforcement bar occurring in succession has to be considered one by one. This is particularly problematic when simulating SCC casting, since this type of concrete is typically used for heavily reinforced structural members. However, the wide use of numerical tools for casting prediction in practice is possible only if the tools are user-friendly and simulations are time-saving.
In order to shorten simulation time and to come closer to a practical tool for casting prediction, instead to model steel bars one by one, this thesis suggests to model zones with arrays of steel bars as porous media. Consequently, one models the flow of SCC through a reinforcement zone as a free-surface flow of a non-Newtonian fluid, propagating through the medium. By defining characteristic parameters of the porous medium, the influence on the flow and the changed (apparent) behaviour of concrete in the porous matrix can be predicted. This enables modelling of any reinforcement network as a porous zone and thus significantly simplifies and fastens simulations of reinforced components’ castings.
Within the thesis, a computational model for SCC flow through reinforced sections was developed. This model couples a fluid dynamics model for fresh concrete and the macroscopic approach for the influence of the porous medium (formed by the rebars) on the flow. The model is implemented into a Computational Fluid Dynamics software and validated on numerical and experimental studies, among which is a large-scale laboratory casting of a highly reinforced beam. The apparent rheology of concrete within the arrays of steel bars is studied and a methodology to determine unknown input parameters for the porous medium is suggested. Normative tables defining characteristic porous medium parameters as a function of the topology of the rebar zone for different reinforcement cases are generated. Finally, the major contribution of this work is the resulting numerical package, consisting of the numerical solver and the parameter library. The thesis concludes on the ability of the porous medium analogy technique to reliably predict the concrete casting behaviour, while being significantly easier to use and far less time consuming than existing tools.
The study introduces the porous medium model for the simulation of concrete flow through highly-reinforced sections. It shows that numerical simulations can predict concrete behavior during casting and help to avoid expensive mistakes.
This study focuses on concrete flow in presence of obstacles and develops a mathematical model and a computational approach for SCC flow through reinforced formworks. In order to decrease high computational times needed to simulate castings through reinforced elements, an innovative approach to model the reinforced sections as porous media is proposed here. In the previous work, this numerical model is proved able to simulate the free-surface flow of non-Newtonian fluids through the reinforcement networks. In the present study, the applicability of the model on the concrete flow will finally be proved. The large-scale form-filling experiments with SCC will be conducted and the experiments will be simulated using the proposed numerical model. The numerical model will then be validated through the comparison of the experimental results and the results of the numerical simulations.
Numerical simulations of concrete castings are complex and time consuming. In order to decrease simulation time and to simplify simulation procedure, an innovative modelling approach, which treats reinforced sections in a formwork as porous media, was proposed. In the previous studies, this numerical model was proved suitable to simulate casting of model yield-stress fluids through reinforced elements. This article focuses on the experimental validation of the proposed model at the concrete scale. For this purpose, a large-scale laboratory casting of a highly reinforced beam is performed. The casting process is numerically simulated and the numerical results are compared to the experimental measurements.
Computational modeling of fresh SCC flow is a comprehensive and time consuming task. The computational time is additionally increased when simulating casting of reinforced sections, where each single reinforcement bar has to be modeled. In order to deal with this issue and to decrease the computational time, an innovative approach of treating a reinforcement network as a porous medium is applied. This contribution presents the model for concrete flow through reinforced sections, based on Computational Fluid Dynamics (CFD), coupling a single-phase flow model for SCC and a continuum macroscopic model for porous medium. In the last part of this paper, numerical simulations are compared with experimental results obtained on model fluids.
Although being a very promising area of concrete technology, computational modeling of fresh concrete flow is a comprehensive and time consuming task. The complexity and required computation time are additionally increased when simulating casting of heavily reinforced sections, where each single reinforcement bar has to be modeled. In order to improve the computation speed and to get closer to a practical tool for simulation of casting processes, an innovative approach to model reinforced sections is proposed here. The basic idea of this approach is to treat the reinforcement zone as a porous medium in which a concrete is propagating. In the present paper, the numerical implementation of this concept is described. A methodology allowing for the computation of the equivalent permeability of the steel bars network is suggested. Finally, this numerical technique efficiency is evaluated by a comparison with experimental results of model fluids casting in model formworks.
The paper addresses numerical modelling of fresh self-compacting concrete. In the previous studies, a numerical tool for casting prediction is built based on the assumption that fresh concrete behaves as a yield-stress fluid and treating zones with rebars as porous media. The present contribution discusses the determination of material parameters, which are required as an input for numerical simulations of casting processes.