Additives of graphene nanomaterials for the improvement of cementitious compositions, cementitious composition, a process for preparing a reinforced concrete, a reinforced concrete and its use

A cementitious composition comprising cement and an additive of graphene nanomaterials, the additive including a mixture of graphene nanofibers, graphene oxide (GO), a dispersing agent (D) and a superplasticizer (SP), wherein said mixture comprises at least two different graphene nanofibers, selected among:

• graphene nanofibers of high specific surface area (GNF-HS), in an amount of between 10% and 75% by weight with respect to the additive, having an area comprised between 260 to 400 m2/g and length of 0.02 to 2 μm;
• graphene nanofibers of low specific surface area (GNF-LS), having an area comprised between 70 to 249 m2/g and length of 0.02 to 2 μm;
• or
• graphene nanofibers of long length (GNF-LL), with a specific surface area comprised between 30 to 100 m2/g and a length of 5 to 200 μm,
• wherein the superplasticizer (SP) is a polycarboxylate ether-based superplasticizer (PCEs) or a sulfonated superplasticizer,
• wherein the amount of dispersing agent (D) of the additive is of about 1% on the total weight of the graphene nanofibers and graphene oxide,
• wherein the graphene nanofibers have an average diameter comprised between 2 nm and 200 nm, and
• wherein the additive contains a total amount of graphene nanofibers and graphene oxide of between 0.0002% and 0.002% by weight with respect to the weight of the cement in the cementitious composition.