The consumption of polymeric materials and their waste increases considerably throughout the world, leading to a constant concern with alternative recycling routes. Polypropylene (PP) waste is produced in large volumes, but it is not recycled in an expressive way. A significant amount of research has been conducted to recycle discarded material into cement-based composites, combining environmental, economic, and technological issues. Nondestructive tests, such as ultra-pulse velocity (UPV), can be used to characterize and estimate the physical and mechanical properties of cement-based materials. This work investigates the effect of the partial replacement of natural aggregates (NA) with recycled PP aggregates on the pulse velocity and physic-mechanical properties of impact-compacted mortars and their correlations. Coarse particles of PP (at 4–10 US-Tyler and 10–20 US-Tyler) provided better mechanical behavior to composites than fine particles (20–50 US-Tyler), the latter being responsible for a rise in porosity. UPV can be used to predict the physical and mechanical properties of mortars containing PP aggregates.