Starter system for concrete construction joints, said starter system comprising: - a casing the interior volume of which defines a housing of flattened shape, this casing being made up of at least a first wall comprising a plurality of through-orifices and a second and a third wall, these latter walls being arranged one on each side of the first wall in orientations substantially perpendicular to the plane of the first wall, each of the walls (3, 5, 6) having an interior surface and an exterior surface, - at least one pair of reinforcing bars (7, 7bis) arranged through orifices in the first wall, each reinforcing bar (7, 7bis) comprising a hoop-shaped first part projecting at the exterior surface of the first wall and a second part produced by a pair of branches projecting at the interior surface of the first wall, each of these branches structurally extending a respective end of the hoop while being arranged inside the housing, in a plane substantially perpendicular to the plane of the hoop, the pair of reinforcing bars (7, 7bis) comprising a first reinforcing bar the branches of which are arranged in the one same plane as the branches of the second reinforcing bar, - the branches of the first reinforcing bar are arranged in such a way that the separation of their free ends is less than the separation of the respective ends of the corresponding hoop, said starter system for concrete construction joints being characterized in that: - the branches of the second reinforcing bar are arranged so that the separation of their free ends is greater than the separation of the respective ends of the corresponding hoop, and in that - the branches of the first reinforcing bar are positioned between the branches of the second reinforcing bar. - a casing the interior volume of which defines a housing of flattened shape, this casing being made up of at least a first wall comprising a plurality of through-orifices and a second and a third wall, these latter walls being arranged one on each side of the first wall in orientations substantially perpendicular to the plane of the first wall, each of the walls (3, 5, 6) having an interior surface and an exterior surface, - at least one pair of reinforcing bars (7, 7bis) arranged through orifices in the first wall, each reinforcing bar (7, 7bis) comprising a hoop-shaped first part projecting at the exterior surface of the first wall and a second part produced by a pair of branches projecting at the interior surface of the first wall, each of these branches structurally extending a respective end of the hoop while being arranged inside the housing, in a plane substantially perpendicular to the plane of the hoop, the pair of reinforcing bars (7, 7bis) comprising a first reinforcing bar the branches of which are arranged in the one same plane as the branches of the second reinforcing bar, - the branches of the first reinforcing bar are arranged in such a way that the separation of their free ends is less than the separation of the respective ends of the corresponding hoop, - the branches of the second reinforcing bar are arranged so that the separation of their free ends is greater than the separation of the respective ends of the corresponding hoop, and in that - the branches of the first reinforcing bar are positioned between the branches of the second reinforcing bar.