A method for making parallelepiped square cross-section formwork modules for building constructions, cut-off walls, embankments, dams, anti-erosion and anti-seismic foundations, starting from used pneumatic tires, characterized in that said method comprises at least the steps of: a) providing a used pneumatic tire (P) deriving both from a periodic replacement of worn tires or from the rubber industry wastes or from the recovering of used pneumatic tires; b) removing from said pneumatic tire (P) the two sidewall iron beads; c) performing cuts (T1, T2, T'1, T'2, T3, T4, T'3, T'4) at diametrically opposite positions on the edges, said cuts defining cut-out regions separated by a middle solid region (T5) of the tire sidewalls; d) removably mounting said pneumatic tire (P) on basket-drum supporting means (C); e) pressing in diametrical directions towards a center of said pneumatic tire (P) the tread portions of said pneumatic tire near said cuts thereby causing said tire to assume a parallelepiped configuration, of a square cross-section; f) pressing the corner regions of said square configuration toward the center of said pneumatic tire and simultaneously continuing said pressing step thereby defining, at said cuts, U-shaped hollow ribs substantially extending through the overall width of said pneumatic tire (P), from a sidewall to the other sidewall of said pneumatic tire (P); g) providing a plurality of locking elements for locking the arms of each said U-shaped hollow rib and related connecting means; h) providing a corresponding plurality of substantially laminar flat upright elements (M); i) locking the arms of each said U-shaped hollow rib and simultaneously locking to each outer wall of each of said arms of the two walls of each said U-shaped hollow rib a respective pair of said upright elements (M); l) introducing the pneumatic tire (P) having assumed said parallelepiped configuration, and supported by said supporting means (C), into a heating and/or cooking oven; m) withdrawing the pneumatic tire (P) from said oven and cooling it to definitively fix said parallelepiped configuration. a) providing a used pneumatic tire (P) deriving both from a periodic replacement of worn tires or from the rubber industry wastes or from the recovering of used pneumatic tires; b) removing from said pneumatic tire (P) the two sidewall iron beads; c) performing cuts (T1, T2, T'1, T'2, T3, T4, T'3, T'4) at diametrically opposite positions on the edges, said cuts defining cut-out regions separated by a middle solid region (T5) of the tire sidewalls; d) removably mounting said pneumatic tire (P) on basket-drum supporting means (C); e) pressing in diametrical directions towards a center of said pneumatic tire (P) the tread portions of said pneumatic tire near said cuts thereby causing said tire to assume a parallelepiped configuration, of a square cross-section; f) pressing the corner regions of said square configuration toward the center of said pneumatic tire and simultaneously continuing said pressing step thereby defining, at said cuts, U-shaped hollow ribs substantially extending through the overall width of said pneumatic tire (P), from a sidewall to the other sidewall of said pneumatic tire (P); g) providing a plurality of locking elements for locking the arms of each said U-shaped hollow rib and related connecting means; h) providing a corresponding plurality of substantially laminar flat upright elements (M); i) locking the arms of each said U-shaped hollow rib and simultaneously locking to each outer wall of each of said arms of the two walls of each said U-shaped hollow rib a respective pair of said upright elements (M); l) introducing the pneumatic tire (P) having assumed said parallelepiped configuration, and supported by said supporting means (C), into a heating and/or cooking oven; m) withdrawing the pneumatic tire (P) from said oven and cooling it to definitively fix said parallelepiped configuration. <EOS>