FEHS – BUILDING MATERIALS INSTITUTE | INSTITUTE OF NON-METALLIC MATERIALS

The thermal history of granulated blast furnace slag and its impact on reactivity

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1 World-wide production of pig iron, blast furnace slag and steel slags

2 Several exemplary GBS, No. 3 (left),
No. 13b (middle) and No. 14 (right)

3 Parameters with influence on the properties of granulated blast furnace slag [2]

4 Schematic dependence of glass enthalpy on cooling/heating conditions

5 Small sample chamber for Differential Scanning Calorimetry

6 Measured and calculated dynamic viscosity of liquid blast furnace slags

7 Particle size distributions of ground GBS 3, 13b and 14 being used for heat of hydration and mortar strength tests

8 Heat capacity curves of GBS 14 after wet granulation (left) and after annealing at 0.93 x T_gfor 24 h (right). The red curve represents the heat capacity of the first upscan (c_p1), while the black line represents the heat capacity of the second upscan (c_p2) after standard cooling at 10 K min^-1

9 Dependence of the fictive temperature T_fon the annealing time

10 Temperature dependence of viscosity of GBS 3. Line is best fit through the data using MYEGA viscosity model [9]

11 XRD of GBS 13b before (left) and after (right) 24 h annealing procedure

12 Fraction 40-63 µm of crushed GBS 13b (above) and GBS 14 (below) before (left) and after (right) 24 h annealing procedure (transition light microscope)

13 GBS 13b before (above, left), after 90 min (above, right), after 24 h (below, left) and after 96 h (below, right) annealing procedure (reflected-light microscope)

14 Slag cement mortar strength for original and annealed GBS

15 Dependence of the slag cement mortar strength on the fictive temperature of GBS

16 Heat of hydration for original and annealed GBS 3, 13b and 14

Many approaches have been developed to evaluate the reactivity of GBS in cementitious systems based on glass content, chemical composition, fineness, etc. However, a general method could not be found. The basic idea of a research project was to use already established analytical techniques. With Differential Scanning Calorimetry and viscosity measurement, in combination with classical cement-based tests, a correlation between the thermal history of GBS and its reactivity in a blastfurnace cement could be demonstrated for the first time.

About 400 million t of blast furnace slag are produced annualy world-wide, together with about 1247 million t of hot metal (2018). About 300 million t are quenched forming the glassy granulated blast furnace slag (GBS). For more than 130 years the GBS has been used as a clinker substitute in cement and concrete due its latent hydraulic property. Many approaches were developed in order to evaluate GBS reactivity in cementitious systems based on glass content, chemical composition, fineness, etc. However, a general method could not be found. Only a rough differentiation might be possible....

TEXT Dr.-Ing. Andreas Ehrenberg, FEhS – Building Materials Institute, Duisburg/Germany,
Dr. phil. Natalja Romero Sarcos, M.Sc. Daniel Hart, Dr.-Ing. Hansjörg Bornhöft, Prof. Dr.-Ing. habil. Joachim Deubener, Institute of Non-Metallic Materials, Clausthal University of Technology, Clausthal-Zellerfeld/Germany

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The thermal history of granulated blast furnace slag and its impact on reactivity

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ZKG 4/2020