|Research projects_27||[email protected]||Innovative measuring method for chloride transport in concrete|
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.
|Research projects_41||[email protected]||Air demand of bottom outlets – Prototype measurements|
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.
|Research projects_42||[email protected]||Large-scale implementation of soil bio-improvement for a series of engineering applications|
In ecology, sustainability stands for a system’s capacity to endure changes and sustain its productivity and, ultimately, its existence. In engineering and construction, sustainability has been associated with the goal to provide long-term safety to man-made infrastructures, reduce their energy needs and minimize their impact on the natural environment. This is the only way for engineering works to meet the needs of both current and future generations. The introduction and development of novel, “smart” materials, has unleashed a vast potential in increasing the sustainability and environmental performance of constructions. This is the case of the Microbially Induced Calcite Mineralization (MICP) for soils which aims at introducing a new paradigm for improving soils and redefining, at the same time, the role of earth as a building material. The technique is inspired by the natural process of the bio-mineralization of calcium carbonate crystals and has at its core the metabolic activity of the soil bacterium Sporosarcina Pasteurii.
The project «Large-scale implementation of soil bio-improvement for a series of engineering applications», funded by the Lombardi foundation, puts the focus on the “bio-improved geo-material”, which is currently engineered at the Laboratory of Soil Mechanics (LMS) of the Swiss Federal Institute of Technology in Lausanne (EPFL). So-far, the soil bio-cementation technique has been studied and controlled at the LMS in multiple scales, ranging from the scale of a few micrometres to that of real engineering applications. The project allows investigating the technique at the large experimental scale, where the soil bio-cementation will be studied under various scenarios, for its potential to offer solutions in a series of engineering problems including: the stabilisation of soils and slopes and the restauration of week foundations, the enhancement of soil-structure thermal interactions for an efficient energy performance of buildings and the protection of soils against erosion.
|Research projects_43||[email protected]||Stress state identification in tunnels via continuous deformation monitoring under coring|
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.
|Research projects_74||[email protected]||Two-component mixes used for backfilling in mechanized tunnelling|
The instantaneous filling of the annulus that is created behind the segment lining at the end of the tail during shielded TBM advance, is an operation of paramount importance for a correct tunnel construction and design. A perfect filling operation minimizes surface settlements, blocks seg-ments in the designed position, bears the back-up load, ensures the uniform contact between ground and linings, avoiding punctual loads, and increases the waterproofing of the tunnel segment lining.
To correctly achieve these goals, a simultaneous backfilling system is necessary and the injected material should have specific mechanical properties.
A two-component system injection is progressively substituting the use of traditional mortars due to the large number of advantages and to the fact that this mix reaches after the mixing immediated gelling and hardening. Despite the large number of applications worldwide, there are no generally accepted recommendations or guidelines for testing this type of grout. Various laboratories use different procedures, making therefore impossible an easy comparison of the results and designers often require different performances and/or property threshold values, based on their personal ex-perience. Furthermore a “trial and error” approach is frequently applied by construction companies on the job sites.
Due to this knowledge gap, the laboratory of “Tunneling and Underground Space” at the Politecnico di Torino started a research project whose aim is to define and to optimize a uniform laboratory testing procedure and to performed a wide set of tests varying, in a parametric way, the mix de-sign, to understand the influence of each component on the final property of the mix. A special at-tention is given on the durability of these type of materials, also when high water pressure is pre-sent.
The research is performed within the framework of a PhD program at the Department of Environ-ment, Land and Infrastructure Engineering at Politecnico di Torino.
|Research projects_79||[email protected]||Residual capacity life cycle evaluation of bridges and viaducts|
In designing civil engineering systems, particularly bridges, viaducts, and infrastructure networks, the system performance must be considered as time-dependent. Therefore, a consistent design approach should comply with the desired performance not only at the initial stage when the system is supposed to be in the intact state, but also during its expected life-cycle. This can be achieved by taking into account the effects induced by unavoidable sources of damage and by eventual maintenance interventions under uncertainty.
In recent years a considerable amount of research work has been done and relevant advances have been accomplished in the fields of modeling, analysis, design, monitoring, maintenance and reha-bilitation of deteriorating civil engineering systems. Nowadays these developments are perceived to be at the heart of civil engineering, which is currently undergoing a transition towards a life-cycle oriented design philosophy.
In such a context, the decommissioning of Grosseto viaduct in Turin, almost at the end of its 50-year service life, represents a significant opportunity for an important research project based on a wide experimental campaign. Experimental investigations are aimed at collecting a large amount of data related to residual capacity of RC/PC existing bridges exposed to different environmental ag-gressiveness (traffic emissions, sulphate attack, chlorides ingress…).
The research project is promoted by Lombardi Engineering with the scientific coordination of Politecnico di Milano in collaboration with Politecnico di Torino, Piedmont Region, Turin Municipality and other public authorities and private companies. This experimental investigation is unique at na-tional and international levels for the variety of information which it could provide to support the safety assessment and residual lifetime evaluation of existing bridges built over the last decades. The research project will consist of several coordinated activities aimed at effectively gathering, synthetizing and processing the data collected during the experimental investigations.
The results of the project can represent solid knowledge foundations for the public authorities in-volved in the management of bridges and transportation networks. Moreover, the results can be exploited for the calibration of methods for safety assessment of existing structures and for the development of life-cycle design frameworks able to properly consider the effects of aging of ma-terials and deterioration phenomena. This will allow to assess the condition state of existing bridges and to predict the evolution over time of the structural performance and the residual lifetime, which represent important information for public authorities to effectively allocate economic resources over time for inspection, monitoring and preventive and corrective maintenance of existing infra-structures.