The increasing research interest in the reuse of waste plastics have presented vast potentials for improving concrete properties and contributing to sustainable concrete production. This work studied the sorptivity behaviour of grades M25 and M50 concretes prepared using pulverised high density polyethylene (HDPE) immersed in 20% hydrogen peroxide as treatment. As an additive, the pulverised HDPE was added to the concrete at 0 %, 0.25 %, 0.5 %, 0.75 %, and 1 % based on cement weight. The concrete had been made with 150 mm3 steel moulds using mix design method. A super plasticiser -Hydroplast-500, was used in the mixes. For the grades M25 and M50 concretes, respectively, 0.4 and 0.36 water/cement ratios had been selected to represent medium and high strengths concretes after 7, 28, and 90-day periods of water cure. After being taken from the water and dried, the concrete cubes underwent a sorptivity test. Results obtained indicated that incorporation of treated HDPE to the concrete reduced its sorptivity up to 59 % and 64.5 % respectively for grades M25 and M50 concretes due to the admixture's existence in the mix. The study recommends concrete prepared with 1 % HDPE by weight of cement for use in water retaining structures, drainage systems and constructions where damp is a challenge to existing infrastructure.