Mechanical properties and microscopic mechanism of gypsum and polyurethane modified waste slurry

Abstract This study employs a composite method involving gypsum and polyurethane to modify waste slurry to create a recycled roadbed material, aiming to promote the resource utilization of waste slurry. Through unconfined compressive strength (UCS) tests and various microscopic analyses, the mechanical properties and microscopic mechanisms of gypsum-polyurethane modified waste slurry with different moisture content at 1-day curing age were examined. The findings reveal that compared with the matrix doped with gypsum/polyurethane alone, gypsum-polyurethane compounds exhibit significantly better performance. Under normal conditions, the single addition of gypsum and polyurethane modification respectively increased the UCS by a maximum of 194% and 216%, and the optimal proportion of composite modification (I9G20S15) reached the maximum UCS value of 2244 kPa. Under immersion conditions, the maximum increase in UCS for gypsum modification is 347%, for polyurethane modification it is 363%, and for the optimal ratio of composite modification (I9G25S15), the UCS reaches 1417 kPa. Scanning electron microscope (SEM) analysis indicates that polyurethane-modified waste slurry exhibits extensive crystal formation and agglomeration, forming a robust skeleton that improves mechanical performance. On the other hand, gypsum-modified waste slurry demonstrates a cross-linked structure of crystalline hydrates and network stacking, improving mechanical performance of the specimens. Furthermore, under the condition of remixing, specimen pores are filled, leading to enhanced compactness and subsequently increased strength. These findings underscore the potential of gypsum-polyurethane modified waste slurry as a promising material for sustainable road construction applications.