The quarrying and utilization of natural stones such as marble and granite are growing rapidly in developing countries. However, the processing, cutting, sizing, and shaping of these stones to render them functional generates huge quantities of waste and dust. These materials are often disposed of openly in the environment, and their potentially hazardous nature has negative repercussions on both the environment and human health. In this study, marble waste (MW) was used as a filler in the unsaturated polyester resin (UPR) matrix to enhance performance and characteristics while adding value to the waste and minimizing manufacturing costs. For this purpose, samples of UPR/MW composites were produced with 0, 5, 10, 15, and 20 wt.% of MW incorporated into the UPR. A full characterization that focused on the microstructure, thermal stability, and physical and mechanical properties was carried out. The results revealed that the use of 10 to 15% of MW improves mechanical performance, with increases from 17 to 26 kJ/m2, 14 to 17 MPa, and 794 to 1522 GPa in impact strength, tensile strength, and elastic modulus, respectively. By introducing a 20% MW filler, the composite loses its performance, particularly Shore D hardness, and becomes very brittle. Thermogravimetric analysis (TGA) indicated significant thermal stabilization, with a delay in the start decomposition temperature of 28 °C for 20 UPR/MW compared to 0 UPR/MW. Additionally, morphological and microstructural tests, namely, FT-IR, XRD, and SEM analysis, show a microstructural change, including the formation of crystalline phases, enhancing matrix-filler interactions due to the creation of Mg-O and Ca-O chemical bonds and the forming of filler agglomeration at high introduction rates that lead to defects in the microstructure. These results confirmed the mechanical results of the UPR/MW composites.
