Advances in Organic Rheology-Modifiers (Chemical Admixtures) and Their Effects on the Rheological Properties of Cement-Based Materials

Abstract

Organic rheology modifiers, especially superplasticizers and viscosity-modifying admixtures (VMAs), have become key components for the workability optimization of modern concrete. The development of these admixtures is crucial to the further performance improvement of modern concrete under different casting and service conditions. Many of the former reviews have summarized research advances in respect of these admixtures from chemical and material perspectives, focusing on the effects of structure and the performance. In this paper, from a rheological perspective, an overview is provided of the microscale behavior of polycarboxylate (PCE) superplasticizers and VMAs (e.g., adsorption, conformation, and bridging) in terms of the evolution of the microstructure of the paste, the effect of chemical structure on the yield stress, the apparent viscosity and thixotropy of cement-based materials, and the structure design of these admixtures. Most importantly, in addition to a general discussion with assumptions (monolayer adsorption of a “flat” conformation, with each molecule on a single particle; statistical polymer composition), special conditions (e.g., preferential adsorption, depletion effects, hydration modification effects, and the polydispersity of the polymer composition) are discussed. Newly developed admixtures, realized through regulation of the microscale behavior, and by the modification of adsorption, topological structure, and molecular frame, are introduced.

Comparative Study of the Performance of Underwater Concrete between Anionic and Nonionic Anti-Washout Admixtures

“…In conjunction with the experimental program, molecular dynamics (MD) simulations will be performed to elucidate AWAcement-water intermolecular interactions at the nanoscale and microscale [10,11]. These simulations can solve Newton's equations of motion for matrix components to determine atomic trajectories and reveal transient binding phenomena [12,13].…”

On the Flow of a Cement Suspension: The Effects of Nano-Silica and Fly Ash Particles

“…The study showed that the viscosity reached its maximum at 2% nano-silica content, and larger fly ash content increased the viscosity when used together with the nano-silica additives. In addition, researchers have used various additives such as viscosity modifying agents, superplasticizers, and organic chemical admixtures [21][22][23][24]. In this paper, we are focusing on nano-additives and fly ashes since they have been widely used in cementitious materials and exhibit effectiveness in improving the rheological properties of fresh cement and concrete.…”

Rheological behaviour, setting time, compressive strength and microstructure of mortar incorporating supplementary cementitious materials and nano-silica

“… 13 Currently, research on the rheological properties of mortar focuses on the evolution of the microstructure of mortar influenced by organic rheology modifiers, the impact of the chemical structure of mortar on yield stress, the apparent viscosity and thixotropy of mortar, as well as the structural design of organic rheology modifiers such as superplasticizers and viscosity-modifying admixtures. 14 Also, coarse aggregate is excluded in many new generations of cementitious materials, which are the mortar mixtures. Therefore, it is critical to study the rheological behavior of the mortar.…”