Experimental and numerical study of the effect of stress on asr expansions in concrete
- Autores: Joaquín Liaudat
- Directores de la Tesis: Ignacio Carol Vilarasu (dir. tes.), Carlos María López Garello (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2018
- Idioma: español
- Tribunal Calificador de la Tesis: Pere Prat Catalan (presid.), Andrés Enrique Idiart Castellano (secret.), Andreas Leemann (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería del Terreno por la Universidad Politécnica de Catalunya
- Materias:
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- Resumen
This thesis aims at deepening in the understanding of the mechanisms by which the stress state affects the development of concrete expansions and cracking due to the Alkali-Silica Reaction (ASR). With this purpose, a combined experimental-numerical study has been undertaken. For the experimental part of the study, two new experimental setups have been developed and used in an extensive experimental campaign.
The first setup has made it possible to measure, seemingly for the first time, ASR expansion curves at the level of a single interface between a reactive aggregate and a cementitious matrix (mortar or cement paste), as well as to study the formed ASR products by means of SEM images and EDS analyses. The thesis includes results from various series of Interfacial Expansion Tests under different conditions, in order to assess their influence on the kinetics of the measured expansions.
For the second experimental setup, an existing triaxial testing machine has been adapted. With this machine, experimental ASR expansion curves from cubical concrete specimens subjected to three different triaxial stress states have been obtained. The results seem to indicate that the volumetric ASR expansion rate is reduced as the applied volumetric compressive stress is increased. Additionally, there seems to be an increase in the expansion rate in the less compressed direction in detriment of the expansion rates in the most compressed ones.
Based on the results obtained in the experimental study, as well as on published results from other authors, a reaction-expansion mechanism has been proposed that may explain the effects of the stress state on the ASR expansions of concrete. This reaction-expansion mechanism has been theoretically formulated and implemented in a coupled Chemo-Mechanical Finite Element (FE) model. In this model, the chemical and the mechanical problems are solved by means of two different FE codes, coupled via a staggered implementation. Both codes are used to analyse the same FE mesh in which the reactive aggregates are explicitly represented, embedded in a matrix phase representing non-reactive mortar or cement paste.
This mesh includes zero-thickness interface elements which are inserted a priori along all the aggregate-matrix contacts and also along some predefined matrix-matrix and aggregate-aggregate inter-elements boundaries in order to represent the main potential crack paths. In the case of the aggregate-matrix contacts, the interface elements also make it possible to represent the specific properties of the Interfacial Transition Zones.
The chemical formulation consists of three primary diffusion/reaction fields for aqueous silicate, calcium and alkalis in the pore solution, complemented by a number of chemical kinetics and chemical equilibrium equations. The dissolution/precipitation reactions involved in ASR expansions are considered to occur only within the zero-thickness interface elements representing fractures and aggregate-matrix contacts, while diffusion of primary species may occur within interface as well as continuum finite elements. The volume fraction distribution of the solid chemical species (reactive silica, portlandite, and ASR products) associated to the interface elements evolve with the progress of the reactions.
From a mechanical point of view, the interface elements are equipped with an elasto-plastic constitutive model based on concepts and parameters of non-linear fracture mechanics. In contrast, the continuum elements are assumed to behave linear elastically. Thus, the mechanical non-linearity of the overall model is due exclusively to the zero-thickness interface elements.
The model has been used for simulating a number of ideal and real cases, demonstrating its ability to reproduce experimental observations regarding the effects of concrete stress state on the development of the ASR expansions.
