Characterization of Sodium Silicate-Activated Portland Cement: 1. Matrices for Low-Level Radioactive Waste Forms

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Title: Characterization of Sodium Silicate-Activated Portland Cement: 1. Matrices for Low-Level Radioactive Waste Forms

Author(s): Barry E. Scheetz and Jefferson P. Hoffer

Publication: Special Publication

Volume: 158

Issue:

Appears on pages(s): 91-110

Keywords: portland cement; radioactivity; sodium silicates; wastes; Materials Research

Date: 1/1/1996

Abstract:
The cement/silicate method of solidifying wastes was investigated. Emphasis was placed on the interaction between aqueous sodium silicate and portland cement hydration reactions. A definition of the role which the alkali- silicate plays in increasing the ability of cement hydration reactions to immobilize waste ions was the principal objective. Characterization relied upon calorimetry, X-ray diffraction, microstructural examination by scanning electron microscopy, and monitoring strength development of the waste forms. Increasing additions of sodium silicate to cement pastes accelerate hydration reactions, specifically the hydration of C 3 A and C 3 S, and decrease the presence of portlandite. Effects on compressive strengths of cement pastes were varied; at a water-cement ratio of 0.83, strengths increased with moderate sodium silicate additions, while at higher water-cement ratios, sodium silicate additions decreased strengths.