Lasco, J. D., Madlangbayan, M., & Sundo, M. B. (2017). Compressive Strength and Bulk Density of Concrete Hollow Blocks (CHB) with Polypropylene (PP) Pellets as Partial Replacement for Sand. Civil Engineering Journal, 3(10), 821–830. https://doi.org/10.28991/cej-030917