Influence of Hydrated Lime on Hydration Products, Phase Assemblage, and Mechanical Performance of Cement-Based Mortars

Hydrated lime is widely incorporated into cement-based mortars to improve workability and fresh-state properties; however, its influence on hydration products and mechanical performance remains insufficiently understood. This study investigates the effect of hydrated lime content on the mechanical behavior and microstructural development of cement-based mortars after 28 days of curing. Eight mortar formulations, ranging from lime-free (1:0:6) to lime-rich (1:5:6) mixtures, including intermediate and modified proportions, were evaluated through compressive strength, flexural tensile strength, and consistency tests. The microstructural evolution was investigated using complementary techniques, including X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG/DSC), and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM/EDS). Increasing hydrated lime content improved mortar workability but was generally associated with reduced compressive strength under the curing conditions investigated. The combined characterization techniques indicated progressive modifications in the hydration products and phase assemblage, with increased calcium-rich phases, greater evidence of carbonation, and reduced continuity of the hydraulic matrix as the hydrated lime content increased. The observed microstructural changes were qualitatively consistent with the mechanical behavior of the mortars. The conclusions of this study are restricted to the 28-day curing period investigated, and further research is required to evaluate the long-term influence of hydrated lime on carbonation and durability-related properties. These findings contribute to a better understanding of the role of hydrated lime in cement-based mortars and provide experimental evidence for the optimization of mortar formulations.