Papers by Author: Eddy A.B. Koenders

Abstract: Modelling the rheological behaviour of fresh granular-paste systems is the main aim of this study. The research approach is based on a conceptual idea where the paste-interaction system is explicitly modelled by an interactive two phase particle system. As a first approach the cohesive force-displacement interaction was measured for two ideally shaped glass particles bridged by water. Later on, the water was replaced by cement paste and the attraction force acting on the glass particles was measured for increasing inter-particle distances. The results gave a very good impression of the cohesive forces acting on a granular paste system employed by the cementations material in its fresh state. The Discrete Element Method (DEM) is one of the computational techniques that is applied to simulate the granular-paste system. With this method, the fresh granular-paste system is divided into two phases (aggregate/paste) and is modelled by a single-phase or a double-phase system of DEM elements. At the first step, the interaction forces of the particle-paste system are compared with the experimental results achieved from the particle-liquid measurements and expressed as an explicit function based on local geometrical and physical parameters. Modelling and experimental results show good agreement.

Abstract: For developing a unique model in which the rheological performance of fresh concretes from zero-slump to self compacting concrete can be described, it is necessary to define workability in terms of fundamental physical entities. In order to achieve this, the concept of capillary cohesion from science of granular physics has been considered as the first step for investigation. In this paper, focus is on this concept and providing some preliminary achievements of the experimental work. In wet granular material the presence of liquid generates cohesion between particles and affects the mechanical properties of the granular media to a large extent. For the simulation of the behavior of this material by considering pendular state for liquid content, a discrete element method (DEM) is used. The cohesion between a grain-pair is expressed as an explicit function of local geometrical and physical parameters. In this study emphasis is on static and/or quasi-static situations. Since the cohesion dominates over other effects of the liquid, such as viscosity and lubrication, the effect of the size of particles on the cohesion arising from the liquid bridge is investigated explicitly. Based on experimental results, a closed-formula approximation is developed that can be used to calculate the capillary force acting between two glass spheres as a function of the separation distance for a given bridge volume.

Abstract: The purpose of this study is to establish an analytical formulation for determination of the critical chloride content in concrete. In this study, factors affecting the critical chloride content such as mix proportion, environment, chemical evolution of pore solution with time, carbonation and so on are taken into account. The numerical simulation program of cementitious materials, HYMOSTRUC was utilized for the construction of the formulation. This was expressed as a free chloride content in a mass unit of concrete as a time function.