Influence of the waste treatment on the properties of mortar with end-of-life gypsum

Gypsum boards are widely used in the construction industry due to their versatility, fire resistance, and sustainability. However, their disposal poses significant environmental challenges, including hydrogen sulfide emissions, depletion of natural resources, and increased landfill use. This study investigates the valorization of waste gypsum boards through pre-treatment and recycling processes, aiming to enhance their reusability and reduce environmental impact. The research explores various pre-treatment methods, including granulometric control and thermal processing, to assess their effects on the physical, chemical, and mechanical properties of gypsum waste. Characterization techniques such as X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Thermogravimetric Analysis (TGA) were employed to examine structural transformations. Additionally, tests on density, slump, modulus of elasticity (PUNDIT), and mechanical properties (compressive and flexural strength) were conducted to evaluate material performance post-pre-treatment. The results indicate that thermal treatment significantly enhances gypsum stability by promoting the transition from dihydrate (CaSO₄·2H₂O) to bassanite (CaSO₄·0.5H₂O) and anhydrite (CaSO₄). Higher temperatures improve density, compactness, and workability, while milling increases porosity and stiffness. Among the tested conditions, T150_20 demonstrated the best balance between mechanical performance and stability, suggesting that a 150°C thermal treatment optimizes strength and durability.