Critical assessment of an aging phenomenological model for building materials

The description of aging of construction materials represents a significant issue. According to previous studies, aging is addressed by using experimental approaches which consist in submitting materials to accelerated aging designs in the laboratory. Then, the effect is highlighted by performing measurements at different stages of material aging. These discrete configurations are considered to evaluate the impact of aging at the building scale. Within this context, this research proposes a phenomenological model that describes the aging of a material over time. It assesses the variation in porosity depending on drying and imbibition loads, each expressed by means of an indicator. Also, a cumulative and a moving approach are used to express each load. Afterwards, the model unknown parameters are estimated by solving an inverse problem. The results of the estimation are obtained based on experimental observations of an aging experimental design on hemp concrete. For each load approach, it is shown that the model fits good most of porosity measurements. In particular, the moving approach is better adapted to study the aging of materials. Further, the model of porosity is integrated into equations of heat and mass transfer within porous media. The objective consists in evaluating the impact of aging, with a continuous approach, on the energy efficiency of the material at the wall scale. Based on a case study, the impact is evaluated by assessing the energy efficiency for a first configuration without aging and a second with. Computations of sensible and latent heat fluxes reveal that thermal losses through the wall are underestimated by about 30% when aging effects are neglected. This finding highlights the significance of this phenomenon and encourages its consideration in future building energy simulations.