The goal of this study is in investigating the effect of operating parameters on liquid-phase exfoliation and in testing the effectiveness of concrete modification with mechanically obtained graphene structures. Exfoliation was carried out with a rotor-stator mixer with the blades sliding on the inner surface of the rotor. The initial concentration of graphite in the aqueous suspension and the rotor speed were changed during the experiments. We have presented the results of the effect of these parameters on the processing time and the concentration of multilayer graphene structures formed through exfoliation. The finished suspension was used to prepare concrete samples for testing in compression and bending. It was established for the content of graphene structures of 1 mg/ml in water, used to prepare the concrete that its compressive strength increases by 1.7–2.5 times, bending strength by 1.2–1.5 times. The maximum concentration of graphene structures in the suspension is 1.7 mg/ml for the minimum time achieved at an initial graphite concentration of 50 mg/ml and a rotor speed of 10,000 rpm.