What is the disadvantage of the usage of GGBS in concrete?

If steel manufacturing isn’t local the cost goes up due to transportation costs.

In order to get most of the corrosion resistance from GGBS the ratio reduces the 28 day and ultimate strength of the concrete. But this almost always is quite a bit higher than similar concrete without GGBS.

GGBS can produce a finer surface texture compared to typical concrete. This can affect coatings requiring a mechanical bond rather than a chemical one.

Lastly, if you are worried about specific chemical (corrosion) interactions where your concrete is being placed, the plant was not able to give us a specific makeup of the GGBS additive. They simply stated that the material was within tolerance of GGBS additives. This won’t be an issue for most users, but it was a problem with concrete directly exposed to industrial materials.