<b>Morphological and Mechanical Characterization of Expanded Polypropylene Beads for Applications in Cementitious Composites</b>

<p dir="ltr">Lightweight and extrudable cementitious composites have seen a surge of both scientific and industrial attention in the past few years for applications in intricate building design, efficient material usage, and affordable housing. Many commercialization attempts have faced significant challenges with traditional cementitious mixtures, yielding a need for novel mixtures. In pursuit of these new materials, many studies have combined a variety of lighter-than-cement materials with traditional concrete ingredients. Polymer foams are one of the most successful options for creating lightweight composites; however, they struggle to bond to the cement matrix and often result in drastically reduced mechanical performance. Being highly compressible, these materials also pose a challenge to extrusion as their volume is pressure-dependent, leading to unexpected behavior in a pressure gradient-rich extrusion system. These problems warrant thorough investigation of the fundamental mechanisms at play and development of mechanical models for the composites in both cured and uncured states and under a variety of conditions. The first challenge of this endeavor arises in the detailed characterization of polymer foam beads as their rounded geometry, low density, and low elastic modulus pose challenges to traditional techniques. This work uses a model system of commercially available expanded polypropylene beads (EPP) and an ordinary Portland cement matrix in the development of novel characterization techniques for size, shape, density, and modulus to lay the groundwork for robust mechanical models of lightweight cementitious composites containing polymer foam beads. A more detailed understanding of this basic EPP-OPC system’s physical and mechanical characteristics will enable development of new engineered formulations of lightweight and extrudable cementitious composites.</p>