Development and characterization of air lime-based injection grouts incorporating ground dune sand for the consolidation of historic masonry

Grouting mortars are widely used for the consolidation of historic masonry due to their ability to improve structural integrity with minimal intervention. This study investigates the development and characterization of air-lime-based injection grouts modified with Ground Dune Sand (GDS) as a sustainable finely ground quartz filler for the restoration of historic buildings. Four formulations were produced, including a reference grout and mixtures containing 10%, 20%, and 30% GDS as partial lime replacement. Fresh-state properties, hygro-dimensional stability, mechanical and ductile behaviour, mortar–grout adhesion, and mineralogical, thermal, and microstructural characteristics were evaluated. The incorporation of GDS significantly reduced water demand, bleeding, and shrinkage, leading to improved fresh-state stability and enhanced dimensional behaviour in the hardened state. Mineralogical analyses suggest limited interaction between the GDS and portlandite, as evidenced by the low consumption of the latter. However, no direct evidence of the formation of C–S–H-type phases has been clearly established, while carbonation remained the dominant hardening mechanism, ensuring compatibility with historic materials. Microstructural observations revealed pore refinement and a progressive reduction in carbonation depth with increasing GDS content, indicating a more controlled CO₂ diffusion within the matrix. Although mechanical strength decreased with GDS addition, ductility and mortar–grouts adhesion were markedly enhanced. Among the formulations studied, the grout containing 20% GDS provided the best balance between volume stability, mechanical compatibility, ductile behaviour, and adhesion performance, confirming the potential of GDS as a local and sustainable mineral additive for heritage masonry consolidation.