Decoding thermal performance through microscopy: multi-scale insights into perlite-enhanced sustainable concrete

The concrete production process accounts for 8% of all global carbon emissions worldwide. This urge demands the development of construction alternatives away from cementious material. This experimental study develops six perlite-enhanced concrete admixtures and explores them using multi-scale scanning electron microscopy (100x-10,000x) combined with energy-dispersive spectroscopy to establish quantitative relationships between microstructure and thermal insulation potential. Mixtures included variable quantities of water, cement, perlite, and additives, including gypsum and polymer, resulting in water-cement ratios ranging from 0.57 to 1.88. Elemental analysis shows calcium content ranging from 0.45 mass% in cement-free Sample 6 to 26.71 mass% in Sample 2, while silicon varied from 0.07 to 14.97 mass%. Ca/Si ratios ranged from 1.19 to 3.08, indicating varying extents of pozzolanic reaction. Sample 6 contained 21.15 mass% carbon from the glue binder and 21.79% aluminum content. Porosity ranged from 28% in Sample 3 to 52% in Sample 2, correlating with water content and thermal conductivity estimates of 0.15-0.45 W/m<middle dot>K. Interfacial transition zones measured 10-30 m in width, with narrower zones in low water-cement ratio samples indicating better particle-matrix integration. Gypsum-containing samples exhibited sulfur contents of 4.46 and 0.91 mass%, resulting in the formation of ettringite crystals that bridge the interfaces. Multi-scale imaging captured three pore populations: micropores (<2 mu m), mesopores (2-50 mu m), and macropores (>50 mu m), each contributing differently to thermal transport. The cement-free formulation proved feasible for ultra-low-carbon applications, whereas cement-based samples reduced cement use by 25% with perlite. These microstructure-property insights help optimize perlite concrete for sustainable construction by balancing thermal insulation and structural performance through porosity and interfacial control.