Effect of resting time on rheological properties of glass bead suspensions: depletion and bridging forces among particles
Source: BAM
Concrete rheology fundamentally investigates the flow, deformation and structural build-up of fresh concrete. Since concrete application technologies have become more complex due to higher materials performance specifications, today, rheology has a substantial impact on the overall technology of construction, including mechanical properties, durability and even sustainability. The flow properties of concrete can be manipulated using rheology modifying admixtures, such as superplasticizers or viscosity modifying agents, which liquefy or stabilise the cement paste, respectively. Once added in concrete these admixtures have a nearly instant mutual effect on the rheology and hydration of cement, which changes over the course of time. The change of properties is mainly related to the hydration of cement, which is the reaction between cement and water that eventually leads to stiffening, setting, and hardening of the materials.
The working mechanism of superplasticizer is explained through their adsorption on cement particles and a consequently occurring of steric hindrance between particles, resulting in the better and stabilised dispersion of the system. To better understand the impact of the molecular structure of superplasticizers on particle interactions in different liquid phases, glass beads with similar size as cement particles were used. Glass beads were investigated in the presence of superplasticizers and in an ionic solution that compares to the liquid phase of cement paste. Using this model system, it was possible to demonstrate that changes of the rheological properties over the course of time are not only related to adsorbed but also to non-adsorbed polymers. The main reason for this was found in the change of the hydrodynamic radius of the superplasticizer molecules with time.
Ji Y, Becker S, Lu Z, Mezhov A, von Klitzing R, Wolfram S, et al.
Effect of resting time on rheological properties of glass bead suspensions: Depletion and bridging force among particles.
Journal of the American Ceramic Society. 2024;107:624–639.