•Geopolymer/graphene nanoplatelets composites show an electro-mechanical behaviour.•The value of the charge coefficient d33 is equal to 11.99 pC/N.•Graphene increases stiffness and ultimate strength of nanocomposites up to 0.5%wt.•Graphene clusters are observed at 1%wt. In this work, authors report, for the first time, the evidence of an electro-mechanical behavior in geopolymer/graphene nanoplatelets (GNPs) composites, with the value of the charge coefficient d33, when 1%wt of GNPs is used, equal to 11.99 pC/N. The mechanical characterization of the nanocomposites is provided by using an innovative single test based on the combination of Brazilian disk test and Digital Image Correlation. The greatest increments in Young Modulus (E) and ultimate tensile strength (σT), with values of 17.44 ± 0.67 GPa and 6.26 ± 0.05 GPa respectively, were measured when 0.5%wt of GNPs was used.