Authors: Zhijun Tan, Geert De Schutter, Guang Ye, Yun Gao, Lieven Machiels
This paper investigates the influence of slag particle size on its hydration speed at particle level in the early age. Slags were separated with sieves into groups of different size fractions, considering a wide range of sizes. The chemical compositions of each group were analyzed by X-ray Fluorescence (XRF). Activated by 15% Ca(OH)2 (by mass) at water/powder ratio 1:1, the hydration heat evolution was recorded by isothermal calorimetry up to 84 hours and converted to hydration degree. Based on the hydration degrees and particle size distributions, the rate of increase of hydrating layer thickness of each single slag particle (k value) was calculated. Results reveal that k values of coarse particles are higher than that of fine particles. Coarse particles contain higher content of CaO but relatively lower content of MgO, Al2O3 and SiO2, resulting in higher reactivity index of (CaO+Al2O3+MgO)/SiO2.
Keywords: Blast-furnace slag, Particle size distribution, Reactivity, Hydration degree
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It is well known that cement is the most used construction material in the world. In the mind of most of people, cement is a kind of grey powder and only used as construction material, to build gardens, bridges, road etc. However, we can do more with cement, here are nice pictures showing some stuff made of cement. Creactive!
Even as a guy like me who deals with cement everyday, I really think these items are pretty funny. What do you think you can do using cement? make the most of your imagination, dare to think.
These following conclusions are summarized from the work of Kocaba’s PhD thesis.
- alite: no influence is shown on the consumption of alite measured by XRD.
- belite: the substitution of cement by both slags seems to result in a delay in the hydration of belite in the first days.
- aluminate phase: there is a filler effect using inert filler at about 12 hours of hydration, which shows slag can also has filler effect in the early hydration period. Transformation of AFt to AFm causes cumulative heat shoulder at about 60 hours.
For all systems, slags did not have a strong influence on hydration of C3A phases. Taking into account the low content of C3A and the corresponding error, it was difficult to highlight any relevant difference between blended paste and corresponding pure pastes.
There was no evidence of slag itself reacting and the effect of slag on aluminate phases can be only attributed to a filler effect.
The raw calorimetry curves of pure cement system showed a peak (called IV) which was attributed to monosulfoaluminate reaction just around 60 hours of reaction. In this way, calcium hemicarboaluminate and monocarboaluminate could be some possible AFm phases corresponding to the second peak of aluminate. But there is no evidence of that and it could be some monosulfate. The corresponding XRD patterns did not show any peaks corresponding to AFm phases at early ages which indicate a very low content if they are present.
- Ferite: The slags seem to favour the hydration of the ferrite phase.
Influence of slag on the degree of reaction of cement
From XRD-Rietveld refinement and SEM-IA, the degree of reaction of cement did not seem to be strongly affected by the slag.