Mechanism Underlying Effect Of Competitive Adsorption Between VMA And PCE On Plastic Viscosity Of Cement Paste

Abstract

Viscosity modifying admixture (VMA) is often combined with polycarboxylate superplasticizer (PCE) to secure high stability of self-consolidating concrete by increasing plastic viscosity. However, the blending of these admixtures can lead to competitive adsorption on particle surfaces, which poses challenges to achieve the desirable rheological properties. The objective of this study is to assess key factors affecting plastic viscosity through competitive adsorption between VMA and PCE, and to elucidate mechanisms underlying the variation of these factors during the competitive adsorption process. A total of 94 mixtures prepared with various VMA and PCE combinations and water-to-binder ratios of 0.16 to 0.30 were investigated in this study. The competitive adsorption between VMA with stepwise increased charge density and PCE was first quantitatively measured, and its effect on plastic viscosity was then analyzed using theoretical models. Results indicated that VMA with a high charge density of 75% exhibited a stronger competitive adsorption with PCE compared to VMA with a low charge density of 25%, leading to up to 2.5-fold higher plastic viscosity even when the adsorbed VMA content was fixed. For VMA with high adsorption capacity, the effect of competitive adsorption on increasing plastic viscosity was mainly attributed to the enhanced hydrodynamic interaction between adjacent particles resulting from a significant increase in floc size induced by bridging flocculation and lower interparticle distance caused by PCE desorption. The former factor played a dominant role, accounting for over 80% of the overall increase. In the case of VMA with low adsorption capacity, the increase of plastic viscosity was primarily due to higher viscosity of interstitial pore solution, reduced interparticle distance, increased particle size, and more interparticle contacts, with each factor contributing similarly to the overall increase in viscosity.

Department(s)

Civil, Architectural and Environmental Engineering

Comments

National Natural Science Foundation of China, Grant 52308239

Keywords and Phrases

Cement paste; Competitive adsorption; Superplasticizer; Viscosity; Viscosity modifying admixture

International Standard Serial Number (ISSN)

0008-8846

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2026 Elsevier, All rights reserved.

Publication Date

01 Nov 2026

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