Ground granulated blast furnace slag GGBS and my experiments

In one of my previous article, I mentioned GGBS:

Now with the development of steel-making, a great quantity of slag is discharged. Because the most common technology of iron-making is blast furnace. Let's talk about blast furnace slag, especially granulated blast furnace slag (GBFS).

In the furnace, the molten iron is heavier than the slag so the slag floats above and flow in a different way. Cold water is sprayed to molten slag (prox. 1400 degree) and it is immediately cool down and broken into small particles (less than 5mm in size) with hardly any crystallization. GBFS mainly consists of Ca, Si, Al, Mg. Clinker can be added with iron slag when being ground to produce cement or GBFS itself can be ground (GGBS) and then added to concrete, mortar and grout. 

In Vietnam, we can substitute up to 30% cement with ground granulated blast furnace slag. An estimated of 300kgs iron slag is discharged for every ton of iron.

GGBS is white, contrary to the grey color of cement. GGBS is much cheaper than cement so it profitable to substitute cement with GGBS.

GBFS and GGBS can resist high temperature so it is also used as refractory. I learn that in some plants, they mix GBFS with cement to use in building coking oven.

The finer the particle size is, the more quickly the hydration reaction is speeded up. Because GGBS is really fine, finer than authentic cement, the particles fill the cavity to form a solid block for a better  waterproof ability, prevent the penetration of even sea water so it is applied in coastal construction and can stand in severe environments. Besides, as we can see, the hydration reaction of cement generates heat while GGBS generate no heat, it can be used to make cold concrete and build big blocks.

GGBS itself reacts really slowly in normal environment. I did an experiment with GGBS by mixing it with normal water only and it took several days to become hard. I learn that the alkaline environment can speed up the setting time so I repeat the experiment with lime. This time it took only several hours. I wish I have time and equipment for further experiment to see how much lime is optimal for the reaction.

Quangngai, November, 25th, 2022