The low viscosity of asphalt concrete at T>135°C is necessary for the construction and compaction process of high-quality asphalt concrete layers. Whereas the continuous increase of viscosity with decreasing temperature is desirable for the reduction of permanent deformations during warm periods, so-called top-down cracking may occur in the course of temperature drops during cold periods. In order to explain the complex viscoelastic properties of asphalt concrete, a multiscale model is proposed. Hereby, the viscoelastic behavior of bitumen serves as input and the effect of air voids and aggregates is investigated. The viscous properties of bitumen are identified, using the bending-beam rheometer and the dynamic-shear rheometer, providing access to the viscoelastic material response for different temperature and loading regimes. With the rheological properties of bitumen at hand, the viscoelastic properties of mastic, mortar, and asphalt concrete are determined using continuum micromechanics, employing the...

The transport and mechanical properties of saturated soil drastically change when temperatures drop below the freezing temperature of water. During artificial ground freezing, this change of properties is exploited in order to minimize deformations during construction work and for groundwater control. Whereas for the latter only the size of the frozen-soil body is relevant, which is obtained by solving the thermal problem, the design of the ground-freezing work for support purposes requires information about the mechanical behavior of frozen soil. In addition to the quantification of the improvement of mechanical properties during freezing, information about the dilation associated with the 9% volume increase of water during freezing is required in order to assess the risk of damage to surface infrastructure caused by frost heave. In this paper, a micromechanics-based model for the prediction of both the aforementioned phase-change dilation and the elastic and viscous properties of freezing saturated soil...

An assessment of the structural performance of concrete tunnel linings under fire load is presented for the Lainzer Tunnel, a shallow tunnel recently constructed in Austria. Prior to the installation of the concrete lining at this tunnel, large-scale temperature experiments were conducted, revealing almost no reduction of the lining thickness in consequence of spalling for the employed lining concrete, reinforced by polypropylene fibers. In the absence of spalling, dehydration of concrete under high temperatures is the safety-determining process. Within the thermochemomechanical material model employed for the tunnel-safety assessment presented in this paper, dehydration is described by the decrease of the hydration extent, resulting in the reduction of both stiffness (thermal damage) and strength (thermal decohesion). The distribution of the hydration extent is determined by means of a thermochemical analysis. The obtained results serve as input for the subsequent chemomechanical analysis, providing insi...