Nonlinear elastic response of thermally damaged consolidated granular media

The mechanical properties of consolidated granular media are strongly affected by large temperature changes which induce the development and localization of stresses, leading in turn to damage, e.g., cracking. In this work, we study the evolution of linear and nonlinear elasticity parameters when increasing the temperature of the thermal loading process. We prove the existence of a link between linear and nonlinear elasticity properties. We show that the change of the nonlinear elasticity parameters with the increase in the thermal loading is larger at the lower temperatures than the corresponding change for the linear parameters, suggesting that nonlinear elasticity can be exploited for early thermal damage detection and characterization in consolidated granular media. We finally show the influence of grain size upon the thermal damage evolution with the loading temperature and how this evolution is mirrored by the nonlinear elasticity parameter

Potential effects of optical solar sail degredation on trajectory design

The optical properties of the thin metalized polymer films that are projected for solar sails are assumed to be affected by the erosive effects of the space environment. Their degradation behavior in the real space environment, however, is to a considerable degree indefinite, because initial ground test results are controversial and relevant inspace tests have not been made so far. The standard optical solar sail models that are currently used for trajectory design do not take optical degradation into account, hence its potential effects on trajectory design have not been investigated so far. Nevertheless, optical degradation is important for high-fidelity solar sail mission design, because it decreases both the magnitude of the solar radiation pressure force acting on the sail and also the sail control authority. Therefore, we propose a simple parametric optical solar sail degradation model that describes the variation of the sail film's optical coefficients with time, depending on the sail film's environmental history, i.e., the radiation dose. The primary intention of our model is not to describe the exact behavior of specific film-coating combinations in the real space environment, but to provide a more general parametric framework for describing the general optical degradation behavior of solar sails. Using our model, the effects of different optical degradation behaviors on trajectory design are investigated for various exemplary missions

Steel waste valorisation Steel Slag Waste Effect on Concrete Shrinkage

The concept of sustainability is becoming widespread every day in society, enterprises and institutions. Defining something as sustainable means that the relationship that it establishes with the environment does not represent an aggression or a threat to the latter neither when it is being utilized nor when it stops performing the function for which was designed. To make this happen we need a system in which the main priority is recycling. Everything mentioned above is related to what is called the “Circular Economy”. Concrete is one of the most widely used construction materials in the world. However, the production of portland cement, an essential constituent of concrete, leads to the release of significant amounts of CO22. The global production of concrete represents more than 5% of the anthropogenic emissions of carbon dioxide every year, mainly from the production of cement. The replacement of cement by fly ash and other industrial waste, such as steel slags, is a good example of how resource conservation can be improved and contamination can be reduced. On the other hand, future trends are predicted to increase demand for steel worldwide. Mainly due to the expected improvement in the living standards and demands of underdeveloped populations. The steelmaking process produces a by-product called slag ranging from 10 to 15% per tonne of steel, where reuse is still reduced and much of it is deposited in a landfill. This study presents laboratory test results on the total and autogenous shrinkage of medium strength concrete with partial replacement of cement by slags. Two different slags were tested, namely ladle furnaces slags (LFS) and ground granulated blast furnace slags (GGBFS). The results show the concrete shrinkage behavior when 25% of substitution are used. These data are important to predict future behavior and show that for the substitution dosages used there are no significant divergences for the shrinkage.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Environmental assessment of radical innovation in concrete structures

In the building sector, the contribution of concrete structure to the overall emissions of greenhouse gases is significant. Switzerland is engaged in a 2050 energy strategy where the reduction of the embodied energy of buildings is a key aspect. In this study, we assess the environmental impact of different low energy concrete solutions. The study focuses on technologies that use cement with very high substitution rate (up to 65%) and other tensile resistant materials than steel in order to keep high durability targets. Hybrid wood-concrete structure, low carbon high performance concrete prestressed with carbon fiber reinforced polymer, and ultra-high performance fiber reinforced concrete with synthetic fiber reinforcement are among the studied options. The environmental assessment is done through life cycle analysis using Ecoinvent database for Switzerland and SimaPro software. Results of initial environmental assessment of production of the new technologies present huge energy and emission savings potential for the energy turnaround

Autogenous Deformation and Internal Curing of Concrete

High-performance concrete (HPC) is generally characterized by a low water/binder ratio and by silica-fume addition, which guarantee a low porosity and a discontinuous capillary pore structure of the cement paste. Modern concretes possess some highly advantageous properties compared to traditional concrete, such as good workability in the fresh state, high strength, and low permeability. However, they have also shown to be more sensitive to early-age cracking than traditional concrete. Early-age cracking mainly occurs due to the fact that the deformations of the concrete member are restrained by adjoining structures. In addition, internal microcracking may occur, due to restraint offered to the shrinking paste by the non-shrinking aggregates. A main source of early-age deformations in HPC is autogenous deformation. Autogenous deformation is the self-created deformation of a cement paste, mortar or concrete during hardening. In traditional concretes it is negligible compared to drying shrinkage. However, the low water/binder ratio and the addition of silica fume in HPC cause a significant drop of the internal relative humidity (RH) in the cement paste during sealed hydration and the occurrence of autogenous shrinkage. Despite the growing interest in autogenous shrinkage, no consensus has been reached in the scientific community about its mechanisms neither about measuring methods. Moreover, different strategies aimed at limiting the autogenous shrinkage are debated at the moment. In this thesis, autogenous deformation of cement pastes, Normal Weight Concrete (NWC), and Lightweight Aggregate Concrete (LWAC) were measured. Both Portland and Blast Furnace Slag (BFS) cement were studied. A model for calculating self-desiccation shrinkage of cement paste was proposed and validated with experiments. Shrinkage of NWC was derived with a composite model and early-age expansion of LWAC, a puzzling phenomenon up to now, was explained. Finally, transport of water from saturated lightweight aggregates (LWA) to hardening cement paste was measured with x-ray absorption.Civil Engineering and Geoscience