Examining the response of self-compacting concrete (SCC) to high temperatures contributes greatly to better understand how structures made with this concrete behave in the fire. On the other hand, the use of waste materials in concrete to produce eco-friendly concretes requires knowing and specifying the mechanical features of these concretes for use in concrete structures. Therefore, this research focused on the impact of using polyethylene terephthalate (PET) particles as a substitution for different fractions of fine aggregate (0, 5, 10, and 15%) on the compressive and tensile performance of SCCs for the two cases of no thermal exposure and thermal exposure at 200, 400, and 600 °C. The impact of the volume percentage of PET particles on the freshly mixed SCCs was investigated using the slump flow, flow time, V-funnel, and L-box tests. Afterward, various mechanical features (compression and tension strengths, failure strain, elastic modulus, toughness, strain at peak stress, and stress–strain graph) following thermal exposure were assessed, and some empirical formulas were derived for predicting them. Moreover, the empirical findings of the current work were evaluated against the values estimated by the prediction relationships of different codes, namely ASCE, EN 1994-1-2, and ACI 216. In general, there was proper consistency for lower thermal exposures, while there were underestimations of the empirical values for higher thermal exposures. Based on observations, for the higher exposure temperatures and higher PET substitution level, drops in the mechanical features were more considerable, so that the compressive strength, tensile strength, and elastic modulus decreased by about 60% in the SCC specimen with a PET substitution level of 15% after thermal treatment at 600 °C compared with SCC without PET and heat (reference). At last, based on empirical relationships derived for the mechanical features, a stress–strain relationship was presented to capture the compre
