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

Abstract

This paper provides results of an experimental study on the force-distance relationship between two particles connected by a liquid bridge. This experimental research is based on water bridges and extended to cement paste bridges with the aim to explain and model the rheological behaviour of fresh concrete mixtures, and to create a fundamental basis for developing mixtures with a predefined deformation performance. The research approach is based on a conceptual idea where the mixture is considered as an assembly of mutually interacting “particle-pasteparticle” systems and the rheological behaviour of the mixture is related to the inter-particle interactions. The concept of capillary cohesion in wet granular materials, which describes the interaction between two particles connected by a liquid bridge, is considered the first step in the investigations. The effect of the wettability of the particles on the force-distance relation of two particles connected by a liquid bridge is studied. Static and/or quasi-static situations are in focus, i.e. where the cohesion dominates over other effects generated by the liquid, such as viscosity and lubrication. Tests were carried out using spherical stainless steel and glass particles and water was used as the liquid with a surface tension of σin=0.072 mN/mm. The contact angle between water and glass is about 15° while between water and stainless steel it is about 60°. It is found that the wettability of particles has a great influence on the force-distance relation of the interacting particles. Conclusion is drawn regarding the possibility to use the generated data as a basis for modelling the rheological behaviour of cement-based mixtures. Keywords: Fresh concrete, rheological model, wet granular material, liquid bridge, wettability, contact angle, interaction force