Synergistic effects of preheated polyethylene terephthalate yarns and nano-carbon black particles on the mortar high-temperature performance

The effects of nano-carbon black (NCB) and two types of polyethylene terephthalate (PET) yarns, the general yarn (YPET) and the modified material with heat treatment (H-YPET), are investigated in regard to the initial and residual mechanical properties of mortar at various temperatures. The combination of YPETs and NCB in mortar mitigates the agglomeration effect of NCB and the weak compressive performance of YPET fibre-reinforced mortars (FRM). Meanwhile, preheating alters the surface properties of H-YPETs, improving the strength and thermal stability of mortars. YPET FRMs with NCB present superior mechanical properties at ambient temperature, improving flexural strength (FS) by 44.8 % (7 days) and 43.2 % (28 days), respectively, while demonstrating comparable compressive strength (CS) to the control before and after high temperature exposures. H-YPET FRM (without NCB) present superior thermal durability, enhancing FS by 19.5 % at 28 days, residual flexural strength after 250 °C heating by 2.7 %, residual compressive strength after 250 °C and 400 °C by 8.9 % and 15.8 %, respectively, while demonstrating comparable CS to the control at ambient temperatures. This study provides two novel and promising mortar materials with outstanding mechanical properties and thermal stabilities, contributing interesting and useful insights towards sustainable building materials with the potentials to possess different functionalities.