Abstract: A process for sealing railroad structures in which the ballast is cleared from the track, the ties are placed on blocks 3, prefabricated concrete elements 6 then being placed under each block, concrete is then poured into the spaces 7 between the prefabricated elements and finally after hardening the tracks are again lowered onto the railroad structure. This relatively simple process sequence includes the use of a synthetic concrete, preferably a synthetic microconcrete, which ensures that due to an extremely intimate connection between the prefabricated elements and the concrete in the spaces between these elements a monolithic layer is obtained.