Compatibility of Viscosity-Enhancing Agents and Superplasticizers in Cementitious and Model Systems: Rheology, Bleeding, and Segregation

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Title: Compatibility of Viscosity-Enhancing Agents and Superplasticizers in Cementitious and Model Systems: Rheology, Bleeding, and Segregation

Author(s): N. Mikanovic, J. Sharman, C. Jolicoeur, K. Khayat, and M. Pagé

Publication: Special Publication

Volume: 262

Issue:

Appears on pages(s): 67-84

Keywords: admixtures; bleeding; calcium carbonate; cement; paste; rheology; sedimentation; segregation; superplasticizers; viscosity-enhancing agents.

Date: 10/1/2009

Abstract:
Viscosity-enhancing agents (VEA) are often used to improve the cohesiveness and stability of self-consolidating and underwater concrete. However, because of various types of interactions occurring between the VEA polymers and other components of fresh cementitious systems, the beneficial effects of the VEA is found to depend on the nature of both the VEA and the other the other components, particularly the superplasticizer (SP). Hence, different VEA-SP combinations are found to yield different dose-response effects in application. To investigate the origin and consequences of VEA-SP interactions, the influence of two common VEAs on the properties of cementitious and reference (limestone) systems was investigated through rheological and stability (bleeding and segregation) measurements in the presence of two typical SPs, a naphthalene-based (PNS) and a carboxylate-based (PC) polymer. The rheology of cement and powdered limestone pastes was evaluated through the Kantro mini-slump test and from measurements of yield stress and plastic viscosity in simple shear, and dynamic moduli obtained through oscillatory measurements. The bleeding and sedimentation behaviors were monitored using a multipoint conductivity method. Corresponding rheology and stability data were also obtained on mortars incorporating the same VEA-SP admixture combinations. In these systems, the different VEA-SP couples demonstrate varying compatibility which impact on their performance.