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Chemo-mechanical modelling of the external sulfate attack in concrete
Full text linkThis paper is focused on the modelling of the mechanical consequences of external sulfate attack in concrete structures under partially or fully saturated conditions. To this purpose a weakly coupled approach is developed: first the moisture content is computed through a simplified diffusion model, then a reactivediffusionmodelallowsforthecomputationoftheexpansiveproductsofthereactionoccurringbetweenthe aluminatesofthecementpasteandtheincomingsulfateions,finallythesolutionofanonlinearmechanical problem gives the expansion, the stress state and the degradation induced by the reaction. The mechanical problem makes use of a multiphase elasto-damage model, developed in this work and accounting for both chemical and mechanical damage. The model is validated by simulating various experimental tests on concrete specimens subject to external sulfate attack and then applied to the simulation of a reduced scale structure of a tunnel lining
Multi-phase modelling of concrete affected by sulfate attack. Applied Mechanics and Materials
No full textThis study focuses on the modeling of damage in concrete subject to sulfate attack. The concrete is described as a multiphase material made of a solid skeleton, a fluid phase including water and air and an expanding phase, which exerts a pressure capable of damaging the concrete surrounding the reactive sites. The moisture content is computed through a simplified diffusion model, then a reactive-diffusion model allows for the computation of the expansive products of the reaction occurring between the aluminates of the cement paste and the incoming sulfate ions
A bi-phase model for concrete subject to sulfate attack.
No full textIn the present paper we focus on the numerical simulation of degradation in concrete due to the development of secondary ettringite in the hardened material
(delayed ettringite formation or DEF). This chemical reaction, causing expansion and
microcracking of the material, can occur due to an external or internal sulfate attack. A chemical-diusion model allows for the computation of the amount of expansive products of the reaction. The concrete aected by DEF is then represented as a two-phase material
made of a solid skeleton and an expanding phase, which exerts a pressure capable of
damaging the concrete surrounding the reactive sites. The model is validated on the basis of experimental data on cement mortar specimens reported in the literature
Equivalent stiffness of non-symmetrical cable systems in cable-stayed bridges
No full textCurrently the ideal of aesthetically pleasant design in cable-stayed bridges coincides with the search for lighter configurations that unfortunately are more prone than others to instability as they involve slender elements characterized by remarkable geometrical nonlinearities. At a conceptual and preliminary design stage, take into account this complex element interaction can appear an excessive modelling effort. Therefore, subsystems to preliminary size the main elements are commonly used and refined analyses can be postponed at an advanced design stage. The convenience of having at disposal analytical formulations able to include the main structural features while retaining a relatively simple form is thus evident. Within this framework, in the present work the restraining action offered by the cable arrangement to the pylon displacement is evaluated by deriving an expression for its equivalent stiffness. The inherent nonlinearity of long heavy cables associated to their pronounced sag is considered by applying Dischinger's formula. The formulation derived to study the in-plane behaviour of the subsystem that consists out of the pylon and the cables can be extended straightforward to study the out-of-plane behaviour. Finally the equivalent stiffness can be used, either in analytical formulations either in simplified numerical models, to define the critical loads associated to in-plane and out-of-plane buckling and to consequently size and preliminary design the pylon cross-section
Damage modelling in concrete subject to sulfate attack
Full text linkIn this paper, we consider the mechanical effect of the sulfate attack on concrete. The durability
analysis of concrete structures in contact to external sulfate solutions requires the definition of a proper
diffusion-reaction model, for the computation of the varying sulfate concentration and of the consequent
ettringite formation, coupled to a mechanical model for the prediction of swelling and material degradation. In
this work, we make use of a two-ions formulation of the reactive-diffusion problem and we propose a bi-phase
chemo-elastic damage model aimed to simulate the mechanical response of concrete and apt to be used in
structural analyses
The effect of external sulfate attack on concrete, mortar and cement paste
Full text linkAbstract. The present work reports the results of an experimental campaign started two years ago and still ongoing, aimed to assess the behavior of different cementitious materials subject to external sulfate attack. To this purpose prismatic specimens of cement paste and specimens of mortar and concrete produced with the same Portland cement, were immersed in demineralized water and in different solutions containing 5% and 10% sodium sulfates. The expansion was monitored in time by direct length measurements and the degradation of the stiffness was indirectly obtained through non-destructive ultrasound wave propagation tests. XRD tests and SEM observations evidenced the presence of secondary gypsum in the outer part of the specimens were sulfates penetrated. An increase of the material porosity was also measured in this region
External sulfate attack in structural concrete made with Portland-limestone cement: an experimental study
Full text linkThis experimental study aims to assess the effect of external sulfate attack on structural concrete made with a common Portland-limestone cement. The experimental campaign, lasted about three years, has been performed on standard-sized cylinders (Φ15×30 cm) subject to different exposure conditions. The overall swelling of the specimens due to chemical reactions was monitored in time. SEM-EDS observations and XRD tests were also carried out. Results showed the presence of secondary ettringite causing swelling and micro-cracks formation. The porosity increase due to sulfate attack of the outer skin of the specimens was measured. Ultrasonic measurements and compression tests on cores drilled from the cylinders immersed in different solutions allowed to confirm and quantify the consequent degradation of macroscopic elastic properties
Mechanical characterization of hemp-lime blocks
No full textThis paper is focused on the experimental characterization of the mechanical behaviour of hemp-lime block. To thispurpose two different mechanical test are considered. After a preliminary geometric characterization of blocks and fibers a seriesof compression tests were carried out to characterize the elastic Young modulus and the compressive strength (UCS). Subsequently,a series of two direction stress path tests were carried out to describe the limit state behaviour of the material in term of internalfriction angle and cohesion
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