In consequence, concrete and mortar of the same age and water content should be less permeable
than pure paste. Results of tests, however, indicate that the opposite is true. Data in Fig. 4.2 show the considerable increase in
permeability when aggregates are added to a paste or mortar [4.2, 4.3]. The greater the size of the aggregates, the greater is the
permeability. These results have been analysed by Mehta [4.1], who attributes the permeability increase to the presence of
microcracks in the transitional zone at the interface between paste and aggregates [4.4]. In addition, two phenomena
contribute to this permeability increase: