A concrete structure and its production process for marine or river applications comprising a first layer (6) or outer layer of highly porous concrete and a second layer (7) or inner core integrally formed with or bonded to the first layer (6), said second layer (7) or inner core being made of low-porous or dense seawater or river resistant concrete. A process for producing such a concrete structure comprises a) preparing a fresh concrete mixture, said concrete mixture comprising cement, sand (2) aggregates and water, b) pouring the fresh concrete mixture into a mould (1), c) allowing a portion of the cement paste (3) to segregate from an upper region to a lower region of the mould (1), thereby forming the first layer (6) in the upper part and the second layer (7) in the lower part, d) allowing the concrete to set and cure and e) demoulding the concrete structure. Another process for producing such a concrete structure comprises a) preparing a first fresh concrete mixture, said concrete mixture comprising cement, sand (2) aggregates and water, b) pouring the first fresh concrete mixture into a formwork (8), c) allowing the concrete to set and cure so as to obtain said first layer (6) of porous concrete, d) relocating one wall of the formwork (8) so as to enlarge the same, d) preparing a second fresh concrete mixture, said concrete mixture comprising cement, aggregates and water, e) pouring the second fresh concrete mixture into the enlarged formwork (8) between the first layer (6) and the relocated wall (10) of the formwork (8), f) allowing the concrete to set and cure so as to obtain said second layer (7) of non-porous concrete.
