GGBS with Concrete, Reducing Pollution A SIMPLE GUIDE TO GGBS
What does "GGBS" stand for?
Ground Granulated Blast Furnace Slag
>>How is it made?
GGBS is made from a by-product of the production of pig iron. It is made by grinding the granular material produced by the rapid quenching of molten slags formed during the manufacture of the pig iron.
>>What does it look like?
It is an off-white powder. It has the same main constituents as ordinary Portland cement but in different proportions.
>> How long has it been used in the Concrete Industry?
For over 100 years,
commercial production of GGBS commenced in 1865 in Germany.
It has been used in the UK in concrete production for over seventy years. Production of GGBS commenced in Ireland in 2001.
>> How does it work?
GGBS reacts with water in a similar way to ordinary Portland cement. However its rate of reaction is slower, so it is blended with ordinary Portland cement to allow activation in the concrete mixes to occur.
>> How much is used in concrete mixes?
It is blended with ordinary Portland cement at ratios of 30% to 85%. Its most common blend is 50% for normal concrete mixes. All existing recipes and mixing procedures do not have to be changed with the introduction of GGBS into a plant.
>> How is it transported and stored?
In the same manner as ordinary Portland cement.
>> Will the concrete produced be as strong when we use GGBS?
The concrete produced will be at least as strong as our mixes made without GGBS. Early age strengths e.g. 7 day tests are usually slightly lower. 28 day strengths are usually the same or higher. As the concrete matures, the ultimate strength is much higher than mixes made without GGBS. Some advantages of using GGBS in our mixes.
> Produces a stronger concrete.
> Produces a more durable concrete.
> Produces a more workable concrete. Easier to compact on site. Easier to pump on site.
> Produces a lighter, even and better surface finish.
> It keeps the temperature down in a large mass of concrete. This reduces the risk of cracking while the concrete is curing.
>> Is using GGBS good for the environment?
Yes, its production does not require extraction of any raw materials.
The levels of pollution caused when producing GGBS is much less than that caused during the production of ordinary Portland cement.
Some high profile projects that used GGBS are:
Westlink Toll Bridge
Luas Bridge
Lee Tunnel
Boyne Bridge