The aim of this study is to investigate the cause of the self-cementing properties of recycled aggregates used for pavement base. Clay bricks were added to the recycled aggregates to study the pozzolanic reactions. The evolution of the mechanical performances of the materials was investigated in the laboratory (California Bearing Ratio) and in the field (plate test). Both tests showed that initially, the mechanical performances of recycled aggregates are equivalent or even lower than those of natural aggregates. However, recycled aggregates become much better than natural aggregates with time. Therefore, setting tests, microcalorimetric analysis, and two pozzolanicity tests (pH evolution and consumption of Ca2þ ions) were carried out in a laboratory in order to explain the observations made on the test beds. The microcalorimetric analysis showed that there is only a slight hydraulicity due to residual anhydrous cement content in recycled aggregates. However, the other tests highlight that the presence of clay bricks particles in recycled aggregates results in pozzolanic reactions that can explain the time-evolution of mechanical performances. This study suggests that recycled aggregates have a high added value when they are used as pavement base