This study examines the effects of calcination temperature and binder composition on the physical performance of limestone calcined clay cement (LC3) concrete made with Iraqi kaolin. Kaolin calcined at 400 °C and 750 °C was incorporated into ternary binders containing Portland cement and limestone powder at different replacement levels. Cylindrical concrete specimens were immersed in water, chloride, or sulfate solutions and assessed for bulk density, water absorption, and volume of permeable voids. Among parameters, calcination temperature had the greatest influence on physical performance. Mixtures containing kaolin calcined at 750 °C generally exhibited lower water absorption and permeable void volumes than corresponding mixtures prepared with 400 °C kaolin. The C55L15HK30 mixture achieved the lowest permeable void volume among the LC3 mixtures. Overall, adequate thermal activation of Iraqi kaolin is essential for improving LC3 concrete performance, while optimized binder proportions can partially compensate for reduced clay reactivity.