Mechanical, acoustic, and thermal assessment of mortar embedded with polycarbonate particles obtained from end-of-life roofing sheets

The study investigates natural hydraulic lime mortar specimens in which polycarbonate (PC) particles obtained from milling end-of-life roofing sheets are used as a partial replacement of natural sand. Compared to plastics such as PET, PS and PVC, PC offers exceptional toughness, excellent heat resistance and transparency, as well as good dimensional stability. Since PC is susceptible to weathering, two types of PC waste are considered, which differ by the environmental exposure conditions during the service of the roofing sheets from which they were milled: indoor and outdoor, respectively. PC waste replaces natural sand (NS) at two replacement levels, and specimens are assessed in terms of mechanical, thermal, and acoustic performance. To better highlight the role of PC waste, comparison with control is carried out at different levels of water reducer addition (PCE) so that the same workability is achieved for all admixtures. Besides, to rule out the role of grading, PC particles are replaced by NS that has been sieved to match the grading curve of the plastic particles. In contrast to the general finding associated with plastic waste embedment, it is found that PC addition offers significant mechanical enhancement, both in flexure and in compression, in terms of ultimate strength, which increases by 20% (30%) at low (high) dosage; in terms of dissipated energy, which multiplies by 3–4 times over control; and in terms of failure mode, which transitions from brittle to ductile. Such outcomes appear consistently and are little sensitive to the PC type and to the PCE amount. Indeed, they seem associated with the flake shape of PC particles as well as with the peculiarities of PC. Specimen density is also reduced, which entails an improvement in terms of thermal conductivity that decreased from 0.69 W/(m·K) for the control mortar to 0.48 W/(m·K) at the highest PC content, corresponding to a reduction of about 30%. In contrast, acoustic absorption improved only for selected mixtures. Overall, results show promising potential for PC waste incorporation in mortar matrices, with significant benefits in the direction of waste reduction and reuse.