Use of Polyethylene Terephthalate (PET) fibers to reinforce the performance of self-compacting lightweight concrete (SCLC) is reported. Evaluation and optimization of the fiber addition is based on different properties. SCLC mixes were designed using three volume fractions Vf (0.5%, 0.75% and 1%) and three aspect ratios (l/d = 15, 30 and 45) of fibers. Slump flow, T500, L-box, segregation, density, absorption, porosity, compressive, splitting tensile and flexural strengths, modulus of elasticity, ultrasonic pulse velocity, thermal conductivity, flexural toughness, and impact resistance tests were performed and evaluated statistically. The results indicated that PET fibers in fresh SCLC negatively affected the flowability and passing ability, while they improved the segregation resistance. Compressive strength and modulus of elasticity slightly increased, whereas the tensile strength was significantly improved. Substantial improvements in flexural toughness, thermal and impact resistances were recorded, indicating beneficial enhancement in toughness and ductility. Less desirably, SCLC with PET showed slight increases in absorption and porosity. The statistical analysis showed that the fiber Vf controlled majority of the tested properties rather than the aspect ratio. Based on desirability function and multi-objective optimization, the optimum Vf and l/d were 0.65% and 35.6, respectively. Theoretical obtained values were verified experimentally for all properties with 0 to +/- 5% variance.
