• The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.

International Concrete Abstracts Portal


Title: Dispersed Nano- and Micro-sized Portlandite Particulates via Electrosteric Exclusion at Short Screening Lengths

Author(s): Iman Mehdipour

Publication: Web Session



Appears on pages(s):



Date: 3/28/2021

In spite of their high surface charge (? = +34 mV), aqueous suspensions of portlandite (calcium hydroxide: Ca(OH) 2 ) exhibit a strong tendency to aggregate, and thereby present unstable suspensions. While a variety of commercial dispersants seek to affect suspension stability, and rheology (e.g., yield stress, viscosity) it remains unclear whether electrostatically, and/or electrosterically based additives may be the most effective additives. We show that the high native ionic strength (and pH ˜ 12.6, IEP: pH ˜ 13) of portlandite suspensions strongly screens electrostatic forces (Debye length: ? -1 = 1.2 nm); as a result of which simple Coulombic repulsion alone is insufficient to affect rheology. On the other hand, the longer-range geometrical particle-particle exclusion that arises from electrosteric hindrance is far more effective at affecting rheological properties. We reveal this behavior to be on account of a generalized scaling between the thickness of the adsorbed polymer layer and the observed yield stress reduction. As a result, electrosterically-based dispersants reduce the suspension’s yield stress by nearly 10x at similar dosage as compared to electrostatic action alone. This nature of electrosteric effects allow for the formulation of suspensions wherein the critical solid loading, i.e., at which jamming is observed, to increase from 33 % for a Coulombic repulsion additive to 50 % (volume basis) for an electrosterically-based additive. By identifying the properties which result in the most effective dispersant, new insights are gained for the design of dispersants tailored for concentrated suspensions presenting strong charge screening behavior.