Drying of mortar at ambient temperature studied using high resolution neutron tomography and numerical modeling. (August 2022) - Cheikh Sleiman, Hani
Abstract: The drying of cement-based materials, naturally occurring in most civil engineering contexts, affects their thermal, hydraulic and mechanical properties and is a leading contributor to the loss of their durability potential. The techniques conventionally employed to study this moisture transfer, such as gravimetry weight loss and point-wise sensor-based measurements, are often destructive and cannot characterize the local driving phenomena in 4D (3D+time), essential given the highly heterogeneous nature of the involved processes. Conversely, full-field techniques, and notably neutron tomography, are non-invasive and ideal for measuring the moisture transport process due to the high attenuation of neutron by hydrogen. In this study, the moisture distribution of a set of cylindrical mortar samples was characterized at different hydric states, as imposed through drying in a thermo-hydrically controlled environment (T=20 °C, RH=35%). The lateral surfaces of the samples were sealed to impose a unidirectional moisture flow. The main phases of the mortar (aggregates, cement paste and voids), visible at the 30 μ m resolution adopted, were separated, and saturation profiles were deduced and validated against the mortar mixture ratios and weight loss measurements. Besides the intrinsic interest of the spatio-temporal evolution of the local extracted saturation, these hydric gradients are essential to calibrate numerical models, as the commonly used Finite Element model presented here. A minimization algorithm was developed for this purpose to automate, optimize and ensure a more objective numerical–experimental calibration procedure. This has allowed the identification of key hydric parameters such as the convective exchange coefficient and the intrinsic permeability.