Granulometric disposition and specific surface area of fillers and additives for repair and restoration compounds

Introduction. This paper presents the results of a study of the particle size distribution and specific surface area of natural and manmade materials used as components of repair and restoration mortars for architectural and historical monuments in southern Russia. The aim of the study was to investigate the particle size distribution of eight types of locally sourced mineral materials (dolomite, limestone, marl, shale, gypsum, anhydrite, bentonite, crushed burnt brick) to further elucidate the influence of particle size distribution on the reactivity, hydration, and microstructure of binder systems. Materials and methods. Based on sedimentation analysis of aqueous suspensions of these minerals using Stokes’ law, particle size ranges were determined and specific surface areas were calculated. Results. It was found that anhydrite and dolomite are characterized by the highest dispersion (average size 14–15 µm), ensuring high reactivity and a dense microstructure, while gypsum and bentonite have larger particles (17–25 µm), affecting the water demand of the mixtures. Gypsum has the highest specific surface area (153.1 m 2 /kg), while bentonite has the lowest (86.7 m 2 /kg). Conclusions. The obtained data, based on the theoretical basis of materials science (provides an understanding of the relationship between the structure, composition, production technology and operational properties of materials) and colloidal chemistry (the behavior of dispersed systems, including processes at the phase boundary – adhesion, capillary phenomena), make it possible to substantiate recommendations for the targeted selection of components of repair and restoration compositions to ensure the required balance between strength, adhesion, water absorption and compatibility with the original materials of monuments and form a scientific and practical basis for the creation of authentic, economical and environmentally friendly compositions based on local mineral raw materials.