Basically, Previous concrete has limited amount of fine aggregates and narrow grade of coarse aggregates.
Various Admixtures used are:
-Due to the rapid setting time of previous concrete, RETARDERS or HYDRATION STABILIZERS are used.
-Air Entraining Admixtures are used to prevent the freeze-thaw damage.
-Supplementary cementitious materials such as Fly Ash or Slag can also be used.
Pervious concrete have gap graded aggregate making it perforated.
Any water-reducing admixture will enchance the strength of the previous concrete. Howver, with the addition of water reducing admixture, the cement will tend to settle in a gap graded mix and hence, we will also need to add air entraining admixture.