Investigation of the Main Performance Indicators of Thermal-Insulating Dry-Mix Mortars Based on Shell Limestone Filler and Containing Hollow Glass Microspheres

This paper presents a study of thermal-insulating dry-mix mortars containing shell limestone, shell limestone extraction waste, and hollow microspheres. The effects of shell limestone and fillers on physical, mechanical, and thermal properties were investigated. The microstructure of shell limestone was examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) using a JEOL JSM-7000F scanning electron microscope. The elemental mass fractions confirmed the carbonate nature of the shell limestone raw material (wt.%: O, 50.3–43.7; Ca, 34.1–44.2; C, 15.6–12.1). Finely dispersed fillers, hollow glass microspheres, and amorphous aluminosilicates were found to be suitable for producing a low-density thermal-insulating lime–shell limestone–cement composition. The particle size of the shell limestone powder was 5.67 × 10−6 m, with calcium carbonate (CaCO3) and silica (SiO2) contents of 71.0% and 22.5%, respectively. The shell limestone and microsphere proportions in the binder substantially affected thermal conductivity (0.090–0.113 W/(m·°C)), compressive strength (3.25–4.05 MPa), adhesion strength to the substrate (0.8–1.2 MPa), flexural tensile strength (2.0–2.5 MPa), and water absorption coefficient (0.3–0.5%). The optimum thermal-insulating dry-mix formulation contained, by mass: lime, 25–40%; shell limestone, 15–20%; glass microspheres, 15–20%; amorphous aluminosilicates, 5–10%; diatomite, 2–10%; and cement, 0.5–4.0%.