Many laboratory studies of internal swelling reactions (Delayed Ettringite Formation (DEF), Alkali-Silica Reaction (ASR) or the concomitance of both) are realized on relatively small size samples. Those laboratory samples do not allow to reproduce the real conditions to which is submitted the real concrete in its environment, in terms of kinetics, volume/surface ratio, thermal conditions especially in massive structures. Therefore, a representative massive concrete structure (2.4 x 1.4 x 1 m3) is realized under controlled and optimized conditions for the development of the concomitant ASR-DEF case to allow better observation and understanding of swelling reactions at structure scale. The scale effect on swelling kinetics is demonstrated by an experimental study comparing the evolution of swelling reaction in the massive samples with the evolution in reconstituted concrete laboratory specimens as well as coring specimens. The measurements are to finely describe and help in understanding the evolutionary mechanisms of structural degradation and can be used subsequently as a reference for numerical simulations. Results show different swelling kinetics in function of sample type, conservation environment, size and boundary conditions.