Comparative study on the performance of synthetic hydraulic lime under different curing conditions

Hydraulic lime has attracted growing interest in building and cultural heritage conservation because of its sustainability and good compatibility with original substrates. Its slow early strength development, however, restricts its use in situations where rapid consolidation is required. In this study, a synthetic hydraulic lime (K3) obtained by co-calcination of potassium feldspar and limestone was subjected to standard curing and accelerated carbonation curing, and the drying shrinkage, porosity, mechanical properties, ultrasonic pulse velocity, as well as phase assemblage and microstructural evolution of mortar specimens were compared. The results show that accelerated carbonation markedly alters the reaction process of K3: At the 28th day, porosity is reduced by about 9.7% relative to standard curing, while flexural and compressive strengths increase to 3.20 MPa and 12.54 MPa, respectively. The overall increase in ultrasonic pulse velocity indicates improved internal structural continuity and stiffness. TG-DSC and SEM observations further show that the carbonation environment promotes rapid consumption of Ca(OH)₂ and substantial precipitation of CaCO₃, leading to a dense composite skeleton formed jointly by CaCO₃ and C-S-H. Taken together, the results suggest that appropriate control of the CO₂ curing environment can significantly enhance the early strength and structural stability of synthetic hydraulic lime, providing a practical option for the rapid consolidation and repair of stone relics and historic masonry structures.