According to an article on TU.no (Norwegian), adding graphene to concrete could increase its hardness up to 50%. The article is referencing results from an ongoing study (Swedish) by Chalmers University of Technology in Gothenburg.
Graphene strengthen concrete
(Pictures from nyteknik.se / Johan Liu)
The study is part of a larger research campaign, targeting building a connected highway along the Norwegian coast from Kristiansand to Trondheim, utilizing extraordinary long bridges and undersea tunnels. Ferjefri E39 (TU.no)