Connecting device and method for widening new and old concrete bridges

The invention discloses a connecting device and method for widening new and old concrete bridges. The connecting device comprises a steel butt joint block, a plurality of groups of expansion bolts and a plurality of groups of shear connectors; the butt joint block comprises a shell and a honeycomb core material located in the shell. The honeycomb core material is composed of a plurality of hexagonal hollow columns; the outer side faces of the hexagonal hollow columns located on the edges of the two sides of the honeycomb core material are attached to the inner side face of the shell to form a plurality of thick connecting plates. A plurality of groups of expansion bolts are connected between a plurality of thick connecting plates on one side of the butt joint block and the old bridge; the plurality of groups of shear connectors are connected between the plurality of thick connecting plates on the other side of the butt joint block and the new bridge; each shear connector comprises an internal thread steel sle