Influence of high-temperature exposure on the properties of gypsum-plastic waste composites: Thermophysical and microstructural analysis

Gypsum plasters are a versatile material with a wide range of applications due to their fireproof, thermal, hygroscopic, and acoustic properties. They are commonly used as a coating material to provide passive protection to structural components. Moreover, the construction sector recognizes the potential for gypsum material to address the issue of plastic waste by offering a recycling solution. However, it is crucial to consider the effect of polymeric waste aggregates on the behavior of the gypsum matrix against fire. To address this issue, this study aims to evaluate the impact of high temperature exposure on the microstructural and thermal properties of gypsum composites containing plastic waste. The study compares two different residues, crushed polypropylene (PP) sourced from disposable coffee capsules and nylon (PA6) fibres obtained from discarded fishing nets, with the reference material as partial replacements of the gypsum matrix. The samples are exposed to different high-temperature conditions, including service temperatures (23 +/- 2 degrees C, 150 degrees C, and 300 degrees C) and fire temperatures (1000 degrees C). The physical, thermal, and chemical properties of the new composites are analyzed based on TGA and XRD analysis, and SEM and micro-CT methods to evaluate the effect of plastic residues on the microstructural properties of the gypsum matrix. Additionally, the cracking patterns induced by 1000 degrees C exposure are compared. The study finds that the nature of the gypsum matrix remains largely unchanged after plastic waste addition. However, the low cohesion degree of the interface transition zone (ITZ) between the products of different hydration is a critical feature that must be considered during the heating process. It could significantly affect the mechanical performance of the new composites. Furthermore, it is worth noting that the inclusion of PA6 fibres in the gypsum matrix improves the cracking performance after exposure to fire temperature. This is a result of better heat spread by microcracking generated after fibres melted. In conclusion, this study highlights the potential of using plastic waste as a partial replacement of gypsum matrix in construction applications. However, it is crucial to consider the impact of high temperature exposure on the mechanical performance of the new composites. Further research is needed to optimize the composition and processing parameters of the new composites to ensure their mechanical stability under fire conditions.

Automated summary

Gypsum plasters are versatile materials with various properties. This study evaluates the impact of high temperature exposure on gypsum composites containing plastic waste. The study finds that the nature of the gypsum matrix remains largely unchanged after adding plastic waste but the low cohesion degree of the interface transition zone is a critical feature. Additionally, adding PA6 fibers improves the cracking performance after exposure to fire temperature.