Viscoelastic liquids are characterized by a finite static viscosity and a zero yield stress, whereas soft solids have an infinite viscosity and a non-zero yield stress. The rheological nature of viscoelastic materials has long been a challenge, and it is still a matter of debate. Here, we provide for the first time the constitutive equations of linear viscoelasticity for magnetic wires in yield stress materials, together with experimental measurements using Magnetic Rotational Spectroscopy (MRS). With MRS, the wires are submitted to a rotational magnetic field as a function of frequency and the wire motion is monitored by time-lapse microscopy. The soft solids studied are gel-forming polysaccharide aqueous dispersions (gellan gum) at concentrations above the gelification point. It is found that soft solids exhibit a clear and distinctive signature compared to viscous and viscoelastic liquids. In particular, the wire average rotation velocity equals zero over a broad frequency range. We also show the MRS technique is quantitative. From the wire oscillation amplitudes, the equilibrium elastic modulus is retrieved and agrees with polymer dynamics theory.

Paving materials can negatively impact the urban climate, but knowledge of the thermal and climatic behavior of multilayer urban structures is lacking, particularly under heatwave conditions. To this aim, a laboratory-scale experiment was developed to characterize pavement samples under heatwave conditions. Surface albedo and evapotranspiration are confirmed as the dominant parameters for surface heating. The thermal properties of the underlying layers of pavement structures also impact their behavior and contribution to the urban climate. In particular, the combination of high effusivity and diffusivity of the granite sidewalk structure allow it to exhibit "cool" behavior during the day and "hot" behavior at night despite its relatively high albedo. A solar transmission index is proposed, including both the radiative and the thermal properties of a structure's constitutive layers, to rank structures by their ability to transmit absorbed radiation in depth. Future work with the developed experimental platform will aim to evaluate the performance and optimize the watering method of pavement-watering for different kinds of pavement structures. Keywords: urban heat island; urban paving materials; thermal properties; heat waves Vz downwards conductive heat flux at depth z [W/m²] Subscript/superscript α albedo [-] emissivity [-] n layer n ref/up reflected or upwards z depth [m]