Lightweight screeds made of concrete and recycled polymers: acoustic, thermal, mechanical and chemical characterization

The paper concerns the use of granulated polymeric materials obtained from sheaths of electric wires, mixed with concrete and water to produce under-floors with good sound and thermal insulating performance. This is a possible solution for the re-use of this typology of waste, so to avoid the disposal into landfills. Several configurations of the product were tested in the reverberation rooms of the Laboratory of Acoustics according to ISO 140-8 standard, in order to fully characterize the sound insulating properties; the thermal conductivity was measured through the hot box of the Laboratory of Thermotechnics, according to EN 1934. Also mechanical tests were executed in terms of dynamic stiffness according to EN 29052-1 and compressibility according to EN 12431; a chemical analysis completes the investigation of the mixture. The results show that the product presents satisfying thermal performance, together with good mechanical properties; the chemical analysis of the loose polymers underlined the presence of some chlorinated and polycyclic hydrocarbons. From the acoustic point of view, the sound impact reduction index directly evaluated both with a direct test on the reverberation room and with the indirect estimations through the dynamic stiffness gave results comparable with common materials used for screeds. When the material was tested in conjunction with other typical components of floors, the sound impact reduction index show poorer performance, underlining that the optimization of the acoustic properties has to be done taking into account of the combination with other floor materials.