Reacciones expansivas internas: estudio de los áridos y hormigón de presas
- Autores: Andressa Gobbi
- Directores de la Tesis: Sergio H. Pialarissi Cavalaro (dir. tes.), Marcelo Henrique Farias de Medeiros (codir. tes.), Antonio Aguado de Cea (tut. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2019
- Idioma: español
- Tribunal Calificador de la Tesis: Ignacio Segura Pérez (presid.), Francesc Pardo Bosch (secret.), Celia Varga Fernández (voc.), Renan Picolo Salvador (voc.), Eduardo Pereira (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería de la Construcción por la Universidad Politécnica de Catalunya
- Materias:
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- Resumen
A significant part of the pathologies found in concrete dams is related with the presence of unsound aggregates that react with the cement paste. Such reactions may lead to expansions, causing damage and compromising the durability of the structure. Despite of the most frequent and studied in the literature is the alkali aggregate reaction (AAR), others reactions may cause similar consequences. This is the case of the internal sulfate attack (ISA) from the use of aggregates contaminated with iron sulfides. In presence of oxygen and water these compounds oxidase releasing sulfates which react with the portlandite and aluminates of the concrete. As a result, the secondary gypsum and secondary ettringite generated lead to expansive phenomena.
In spite of the increased number of studies considering ISA and its consequences, deeper insight regarding uncertainties such as how the ISA develops, its differences with respect to AAR from the diagnostic point of view, and if the ISA may occur combined with the AAR is required. In this line, specific experimental methods to predict the risk of ISA is also needed. The strategy adopted by most of the standards and guidelines limit the maximum content of iron sulfides and/or total sulfates present in the aggregate used to produce the concrete. Taking account that part of the iron sulfides do not react due to the protection of the interlocking rock, methods capable to quantify the effective amount that oxidize and is free to react with the phases present in the concrete are required.
The objective of this doctoral thesis is to answer these questions providing information regarding the accelerated evaluation of the sulfates releasing from the oxidation of the iron sulfides. Likewise, deeper study of the ISA in two real damps provides evidences of its development in parallel with the AAR. The work addresses complementary aspects which include the study of different accelerated procedures to evaluate the potential reactivity of the aggregates in terms of maximum release of sulfates and the study of the concrete from dams presenting expansive phenomenon.
Given the need of deep insight regarding the ISA of concrete, this doctoral thesis addresses the following key issues: the study of distinct accelerated procedures to assess the potential reactivity of aggregates regarding the maximum release of sulfates and the analysis of the concrete from two dams subjected to expansive phenomena.
The study of the aggregates assess the effects of the main variables related to the oxidation of the iron sulfides present in the aggregates used to concrete dam production. In this sense, the influence of variables such as: the temperature, the alkalinity of the medium, the aggregate size, the shapes and the time of agitation of the oxidation and sulfates releasing is assessed.
In the case of the concrete, the study deals with the experimental programme performed in two dams: Graus and Tavascán. In both structures, the main pathological manifestations are the expansive problems of internal origin responsible for significant horizontal and vertical movements. The experimental tests allow to confirm the main causes of the anomalous behaviour due to the internal reactions and the expansive behaviour associated. The methodology and the obtained results of several tests performed in the dams and at laboratory with specimens of concrete and samples of aggregates from the quarries are presented.
Complementary, a protocol of operations based on the obtained knowledge with the study of the dams of Graus and Tavascán is proposed. The protocol is a useful tool and guideline to the definition of a methodological approach towards the diagnostic of concrete dams presenting indications of expansions of internal origin.
