Microstructural characterization of an optimized self-leveling sand concrete: Correlating SEM, EDS and XRD observations with mechanical performance

Self-leveling sand concrete (SLSC) shows promising characteristics, but its large-scale development remains limited by insufficient understanding of the microstructural mechanisms governing its engineering performance. This research aims to address this gap through an experimental campaign dedicated to evaluating its engineering performance, combining in-depth microstructural analysis with a new multi-scale investigation for material characterization. The analysis of fresh-state behavior, mechanical property determination (compression tests and ultrasonic measurements for porosity estimation), and microstructural characterization of the hardened state comprise the three complementing components of the study. The morphology and homogeneity of the cementitious matrix were examined using scanning electron microscopy (SEM), and the mineralogical phases and types of hydrates (C-S-H, portlandite, ettringite, and calcite) were identified through chemical microanalysis using energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). Based on the previously optimized self-leveling coefficient (AN = 0.2), the present study investigates the corresponding microstructure. The optimized SLSC formulation showed a dense, homogeneous microstructure devoid of noticeable cracks. The material's good compactness is confirmed by the combined technical analyses (SEM-EDS-XRD), which also show a relationship between the material's composition, mechanical characteristics, and microstructure. These outcomes provide a microstructural interpretation of the previously reported engineering performance of the optimized SLSC formulation and contribute to understanding the relationship between hydration products, matrix compactness, and mechanical behavior.