I read this as less concrete used for any one application. It's also not clear to me that this would reduce net costs, as producing bulk graphene is likely not as cheap as any other conceivable additive. From an environmental perspective, if required volume is reduced but cost is the same, then worldwide consumption could be reduced.

It's cheaper than many other additives.

Graphene flakes are all that is needed for concrete reinforcement, and it's trivial to produce, even at scale. Carbon chunks are thrown into industrial blenders with water and detergent, resulting in graphene flakes sheared and then separated in suspension. The flakes are separated, washed, and dried.

Large graphene sheets are hard. Tiny flakes are trivial, gradeschool kitchen science.

For it to come into effect, the cost of the concrete should be a major part of its usage. This may or may not be true in this case, since there's land costs and a lot of regulations

It's "Jevons", and it is pronounced with a "j" sound.