Glass Content Determination and Strength Development Predictions for Vitrified Blast Furnace Slag


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Title: Glass Content Determination and Strength Development Predictions for Vitrified Blast Furnace Slag

Author(s): R. Doug Hooton and John J. Emery

Publication: Special Publication

Volume: 79


Appears on pages(s): 943-962

Keywords: blast furnace slag; chemical analysis; compressive strength; glass content; pellets; regression analysis; silica flour.

Date: 5/1/1983

The estimated glass content of a vitrified slag is very sensitive to the method employed. The degree of vitrification (i.e., glass content) of a number of slags has been determined by several optical methods and X-ray diffraction. Based on this study, the XRD method is considered the most reliable. In this method the glass content is obtained by comparing the peak intensity ratios of a CaF. 2 internal standard to the mellilite and merwinite peaks in relation to those found for synthetic materials. The "McMaster Optical Method" that involves individual, optical particle analysis under crossed polars can be correlated to the XRD approach for rapid laboratory use. As part of this overall study, it has been shown that the compressive strengths of mortars containing 70 percent ground slag/30 percent portland cement as the binder can be related to the chemical composition, fineness of grinding and degree of vitrification by XRD. Of these parameters, key oxide chemistry and degree of vitrification are most important, with the best correlation at 7 day strengths. Since early strength development is important in applications, the hydraulicity prediction method will be of help during slag selection. However, it still appears that performance criteria (i.e., compressive strength development) are more realistic and should be adopted in specifications.