Role of Functionalized Polypropylene on Chemo-Mechanics of Ductility-Enhanced Cement Beams

This paper studies the chemo-mechanics of cement beams containing polypropylene (PP) functionalized using ultraviolet (UV) irradiation. It is hypothesized that UV irradiation enhances the load transfer at the interface of cement and PP while facilitating the valorization of waste PP. In this study, we use UV-irradiated polypropylene (UVPP) plastic particles as an ingredient in cement paste, using the enhanced cement-UVPP interaction to improve the capacity for load transfer. Using atomic force microscopy based infrared spectroscopy (AFM-IR) on a UVPP-cement composite, we first show that the UV bombardment of PP promoted the formation of oxygen functional groups at the interface between UVPP and cement, indicating a possible increase in the affinity of the UVPP particles toward water and thus their hydrophilicity. This in turn is expected to enable the formation of bonds between the UVPP and cement, enabling stress transfer at the interface. We further show that this stress transfer increases the work-of-fracture, ductility, and mechanical energy absorption of the notched three-point bending cement-UVPP composite beam. This is accomplished when the two fracture surfaces that form during crack propagation are bridged by the UVPP-cement interaction. Since the ductility of these beams is size dependent, we performed fracture tests on two-dimensional (2D) geometrically scaled beams of four sizes. In addition to the mechanical improvements, this work forms the foundation for future work focused on reducing the carbon footprint of structures, since the UVPP replaces some of the cement and eliminates some of the plastic waste from landfills.