A New Recycling Technology to Produce Premixed Thermal Insulating Mortars from Polyurethane Waste Foams

The increasing demand for sustainable construction materials has driven research into the reuse of plastic waste for renewable building applications. This study introduces a new lightweight insulating mortar for floor and roof systems, utilizing recycled rigid polyurethane (PU) foam as the primary aggregate. The binder mainly consists of Portland cement, with no added sand, and includes minor additives to enhance mechanical, physical, and thermal properties. Initial tests demonstrated that key performance metrics—density, compressive strength, and thermal conductivity—are significantly influenced by the PU content. As the proportion of PU increased, all three parameters decreased. The optimized formulation, comprising 92.25 vol.% PU foam, 6.75 vol.% cement, and 1 vol.% additives, achieved a low bulk density of 420 kg/m3, a compressive strength of 1 MPa, and a thermal conductivity of 0.07 W/m·K. A pilot-scale production system with a capacity of 1500 L/h (equivalent to 20 bags of 75 L) was subsequently designed, implemented, and validated. These findings underscore the potential of PU-based lightweight insulating mortars to reduce environmental impact and support the development of sustainable construction practices globally.