Visual atlas of microstructures: Deciphering performance parameters in thermal mortars

The internal structure of coating mortars often displays considerable variability, posing challenges in analysing and comparing their diverse performance characteristics. Yet, employing advanced characterisation and diagnostic techniques offers a pathway to a deeper comprehension of mortar composition and microstructural traits, thereby establishing crucial performance benchmarks. This study investigates the properties of mortars formulated with lightweight aggregates such as expanded cork, expanded clay, and silica aerogel, employing a suite of techniques including X-ray Microtomography (μ-CT), Electronic Scanning Microscopy (SEM), X-ray Diffraction (XRD), Infrared Spectroscopy Fourier Transform (FTIR), and Stereomicroscopy (SM). Through these methods, we conduct a multi-scale analysis of mortar solid structure, delineating aggregates, binders, aggregate/binder interfaces (ITZ) characteristics, and porous structures in quantity, shape, size, and pore connectivity. Additionally, we explore components used in mortar and curing reaction products. Our proposed methodology involves assessing the applicability of each microstructural characterisation technique and its capacity to interpret data from mechanical and physical laboratory tests commonly conducted on hardened mortars. This approach identifies pertinent parameters for microstructural characterisation and proposes a limited number of microstructure groups based on aggregate connection type and porous framework. The correlation of these findings with the macroscopic behaviour of the tested mortars demonstrated that different microstructural arrangements led to significant variations in mechanical and physical properties, such as compressive strength, thermal conductivity, and gas permeability. Such systemization proves invaluable in comparing mortar performance and crafting new formulations, culminating in developing a graphical atlas. • The microstructure of thermal mortars was analysed on a multi-scale study. • SM, μ-CT, SEM, FTIR and XRD were used for microstructure and compositional analyses. • Microstructural groups were identified and classified in a visual atlas. • Microstructural groups and macroscopic properties were shown to be correlated.