Early deterioration in civil infrastructure is mainly caused by chloride-induced corrosion of steel in reinforced concrete. The prediction of chloride transport in concrete is very often based on oversimplified material models, many of which were developed a few decades ago. Most of the required input parameters are either difficult to measure, or are established by empirical equations. This limitation to the application of reliable chloride transport models in practice is specifically addressed by a research project launched at the Institute for Building Materials of the ETH Zürich. Within the framework of a PhD project, which is financially supported by the Foundation Lombardi Engineering, an innovative method to measure the transport coefficient of chlorides in existing reinforced concrete structures will be developed. This measurement method should work on a micron to millimeter scale, being applied on concrete cores taken from real structures. The obtained information shall help to explain how the diffusion coefficient is affected by material variations on the micro-, milli- and centimeter scales, by age as well as by the binding capacity of chlorides. It is aimed to develop in this way not only a relatively fast method, but to get also a more representative idea of the actual processes in concrete structures in order to better understand the “natural” chloride transport in this medium. Involving analytical chemistry techniques and thermodynamic modeling, it is tried to spatially resolve transport information on multiple length scales of interest and in a way to avoid artifacts induced by artificial acceleration. This new analytical procedure refers to quantitative high spatial resolution chemical imaging, which is based on micro analytical techniques using micro- X-Ray Fluorescence. If successful, this innovative method would be much faster than existing procedures and would additionally provide the actual spatial resolution of transport coefficients, which can then be used as reliable input for predictive models on a case to case basis.

Despite the rather good knowledge about the mechanical behaviour of High-Performance Concrete (HPC) at high temperatures, further studies related to spalling (to which HPC is very sensitive) are still required. Spalling presents a complex process, which is especially for tunnels of particular concern. It is a result of a combination of mechanical concrete decay with temperature, pore-pressure build-up due to water vaporization, and stress induced by both thermal gradients and external loads. How these different aspects influence each other is not yet completely understood. In collaboration with the CTG-Italcementi Group, the Politecnico Milan launched therefore a research project with the purpose to investigate the interaction between pore-pressure and stress triggering explosive spalling. This is done by subjecting concrete slabs (800x800x100 mm) to a standard fire on one side. At the same time a membrane compressive stress of 10 MPa is applied and kept constant by means 8 hydraulic jacks as shown in the figure above. The membrane load helps to limit the onset of tensile stress, which might lead to cracking and to the consequent release of vapour. A steel frame restrains the hydraulic jacks, while the whole loading system is located on a small horizontal furnace. During the test, the development of pressures and temperatures is continuously monitored at 6 different depths, and transversal displacements are measured via LVDTs. With this research project, which is co-financed by the foundation Lombardi Engineering, it is expected to obtain a better insight into the actual spalling process and its causes.

Bottom outlets are a key safety feature of large dams. Their primary roles are (i) control of the water level, e.g. during the first impounding, (ii) rapid water level drawdown in emergency situations, e.g. war and terrorist threats, iii) discharge of excess floods and (iv) the flushing of sediments. Future demands on bottom outlet operation will likely increase due to dam heightening as promoted by the Swiss energy strategy 2050 and more frequent sediment flushing following increased reservoir sedimentation. The high-speed free surface flow downstream of the gates results in considerable air entrainment and air transport and consequently negative pressures along the bottom outlet. Therefore, the gate chamber is equipped with an aeration conduit that guarantees sufficient air supply into the bottom outlet. Problems regarding cavitation damage and gate vibrations may consequently be prevented. Up to date, the existing design criteria for the required air demand do not allow for a coherent hydraulic design of bottom outlets. In an ongoing PhD thesis at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of the Swiss Federal Institute of Technology Zurich (ETH Zurich) the air demand and two-phase flow features of bottom outlets are investigated in a large-scale hydraulic model. Prototype measurements are crucial for a proper upscaling and validation of the model results. However, prototype data is scarce, especially for static heads H0 > 80°m w.c. Therefore, the Lombardi Engineering Foundation financially supports prototype measurements in the bottom outlets of Luzzone and Malvaglia arch dams.

The design of new tunnels and the safety assessment of existing ones are made difficult by many uncertainties such as initial stress state and mechanical properties of soil and stress state in the tunnel lining. As regards this latter point, a possible solution is to evaluate the stress state experimentally through different slightly destructive techniques, such as over-coring and under-coring methods. The basic idea is to measure the deformation at the external surface of a R/C member afterwards an hole is drilled orthogonal to the surface. These established techniques provide useful and reliable information for plane stress state, in which the dependency on the investigated depth is negligible. On the contrary, in concrete tunnel linings, the stress state is generally expected to vary along the element thickness due to bending effects. Hence, taking inspiration from the abovementioned techniques, a new method is under development at Politecnico di Milano in order to take into account the variability of the stress state with the depth. In the project at issue, the idea is to monitor the displacement field during coring, in order to investigate an increasing depth of the concrete member along with the progress of hole boring. This analysis is made complex by the non-negligible boundary effect at the bottom of the hole, this making the inverse analysis more complex and the implementation of numerical models mandatory.