Capillary Cohesion between Two Spherical Glass Particles

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.

Simulating the behaviour of fresh concrete with the Distinct Element Method – Deriving model parameters related to the yield stress

“…For purposes of this article only the principal shape of the measured curves and the approximate value of the distance between the particles at reaching the maximum force are essential. The material model at hand is also in good agreement with the experimental results presented by Hoornahad et al [29,30].…”

Towards a Model for Fresh Granular-Paste Systems Based on Discrete Element Method

“…Regarding the results it was observed that the paste behaves quit similar to other liquid materials, and, by assuming the paste to be uniformly distributed over the surface of the particles and the thickness layer surrounding each particle equal to 150 µm (observation), an analytical formula for describing the interaction force arising from the formation of liquid bonds between particles [5] could be derived (Eq. 1).…”

“…The experimental tests were done by considering the glass spheres mimicking the particles for different paste mixtures (Table 1). For each mix, a displacement controlled tensile deformation test is performed by a specially designed experimental apparatus [5]. After covering the particles by an undetermined volume of paste, two particles are brought into contact and then slowly separated incrementally until rupture.…”

Wettability of particles and its effect on liquid bridges in wet granular materials

“…In a static or quasi-static situation, where the cohesion dominates over other effects generated by the liquid, such as viscosity and lubrication, the magnitude of the liquid bridge force is related to the geometry of a liquid bridge [6,7,8]. The geometry of a liquid bridge depends on 1) the characteristics of the particles (shape, size and wettability), 2) the surface tension of the liquid, 3) the volume of the liquid and 4) the inter-particle distance [2,6,9]. In this paper the wettability of solid particles and its effect on the force-distance relation of two particles connected by a liquid bridge is in the main focus.…”