The simulation of transport processes in cementitious materials with embedded healing systems

A new model for simulating the transport of healing agents in self-healing (SH) cementitious materials is presented. The model is applicable to autonomic SH material systems in which embedded channels, or vascular networks, are used to supply healing agents to damaged zones. The essential numerical components of the model are a crack flow model, based on the Navier-Stokes equations, which is coupled to the mass balance equation for simulating unsaturated matrix flow. The driving forces for the crack flow are the capillary meniscus force and the force derived from an external (or internal) pressure applied to the liquid healing agent. The crack flow model component applies to non-uniform cracks and allows for the dynamic variation of the meniscus contact angle, as well as accounting for inertial terms. Particular attention is paid to the effects of curing on the flow characteristics. In this regard, a kinetic reaction model is presented for simulating the curing of the healing agent and a set of relationships established for representing the variation of rheological properties with the degree of cure. Data obtained in a linked experimental programme of work is employed to justify the choice and form of the constitutive relationships, as well as to calibrate the model’s evolution functions. Finally, a series of validation examples are presented that include the analysis of a series of concrete beam specimens with an embedded vascular network. These examples demonstrate the ability of the model to capture the transport behaviour of this type of SH cementitious material system

A review on thermophysical properties and thermal stability of sugar alcohols as phase change materials

The increasing use of renewable energy sources has highlighted the importance of energy storages, and in particular of latent heat thermal energy storages (LHTESs). Among the phase change materials (PCMs) that can be used in such systems, sugar alcohols (SAs) are considered potential substances that may lead to interesting applications in the LHTES sector. In this work, a detailed literature review analysis of six SAs (xylitol, sorbitol, erythritol, mannitol, inositol, dulcitol), their thermophysical properties, their thermal stability and their main LHTES applications is presented for the first time. The thermophysical properties under discussion include melting and crystallization temperatures, latent heats of melting and crystallization, specific heat, thermal conductivity, density and dynamic viscosity. Thermal stability was evaluated by taking into account studies of thermal endurance, degradation temperature and cycling stability. Differential scanning calorimetry (DSC), T -history, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were considered as measurement techniques. Applications include the use of SAs in solar collectors and cookers, heat exchangers, porous materials, absorption cooling systems, mobilized thermal energy storages (M-TESs). New measurements of phase transition properties and degradation temperature for the studied SAs were also carried out by the authors of the present study. A good agreement between the proposed data and the literature values was found. The analysis reveals that some SAs may be considered suitable for low-to-medium temperature LHTES appli-cations, provided that their drawbacks are adequately evaluated and addressed. To this purpose, the study also highlights the most critical aspects that should be considered when developing both fundamental research and engineering applications related to SAs