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Abstract(s)
A interação entre as estruturas de betão armado e a agressividade do meio ambiente, quando ocorrem diferentes ações em simultâneo, proporciona a degradação precoce das mesmas. Desta forma, a sua durabilidade é colocada em causa e o tempo de vida útil para o qual foram projetadas é reduzido. De entre os vários mecanismos de deterioração do betão foram objeto de estudo deste trabalho a carbonatação e os ciclos gelo-degelo. A ação isolada ou conjunta destes mecanismos provoca danos irreversíveis nas estruturas de betão, com consequências graves na sua estabilidade e segurança.
No sentido de avaliar o comportamento do betão face à carbonatação e ciclos gelo-degelo desenvolveu-se um dispositivo de ensaio acelerado de carbonatação onde corpos de prova cilíndricos com condições de cura distintas, em laboratório e sob condições naturais de exposição, são submetidos a concentrações elevadas de CO2 e diferentes humidades relativas. Os ensaios de carbonatação acelerada incidiram sob corpos de prova padrão e corpos de prova degradados pela ação de sucessivos ciclos gelo-degelo. No ensaio de corpos de prova padrão utilizaram-se concentrações de 15, 30 e 60 % de CO2 e variou-se a humidade relativa entre 32, 60, 75 e 90 %. Os corpos de prova degradados pela ação de 8, 12, 16 e 20 ciclos gelo-degelo foram submetidos ao ensaio acelerado de carbonatação sob 60 % de CO2 e 75 % de HR. Foram ainda efetuados ensaios complementares de caracterização de um betão padrão no que diz respeito à sua durabilidade, através de ensaios de absorção por capilaridade e resistência à compressão, microestrutura e composição química através dos ensaios de espetroscopia de energia dispersiva e porosimetria por intrusão de mercúrio, respetivamente. Estes últimos foram realizados antes e após carbonatação.
Constatou-se que o maior avanço da frente de carbonatação, medida com fenolftaleína, é conseguido sob condições de exposição de 60 % de CO2 e 75 % de HR. O incremento do número de ciclos gelo-degelo proporciona uma maior degradação nos corpos de prova, conduzindo a profundidades carbonatadas críticas. Com 16 e 20 ciclos gelo-degelo a profundidade carbonatada obtida em corpos de prova curados em laboratório é cerca do dobro da verificada em corpos de prova padrão. Para o mesmo número de ciclos, os corpos de prova curados em condições naturais carbonatam a 100 %.
Desta forma, é possível afirmar que o dispositivo de ensaio acelerado de carbonatação desenvolvido permite avaliar com precisão os efeitos da carbonatação e gelo-degelo no betão.
The interaction between the reinforced concrete structures and the aggressiveness of the environment, when different actions occur simultaneously, provides their early degradation. Thus, their durability is put in jeopardy and the operating time for which they were designed is reduced. Between the several mechanisms of concrete deterioration, carbonation and freeze-thaw cycles were object of study of this work. The isolated or joint action of these mechanisms causes irreversible damages in the concrete structures, with serious consequences on their stability and safety. To assess the behavior of the concrete in relation to carbonation and freeze-thaw cycles, an accelerated carbonation test device was developed where cylindrical test samples with different maturing conditions, in lab and under natural exposition conditions, are submitted to high concentrations of CO2 and different relative humidity. The accelerated carbonation tests were focused on standard test samples deteriorated by the action of successive freeze-thaw cycles. In the standard test samples have been used concentrations of 15, 30 and 60% of CO2 and the relative humidity had a variation between 32, 60, 75 and 90%. The test samples deteriorated by the action of 8, 12, 16 and 20 freeze-thaw cycles were submitted to the accelerated carbonation test under 60% of CO2 and 75% of RH. Standard concrete characterization complementary tests were also performed in relation to its durability through capillary and compressive strength absorption tests, microstructure and chemical composition through dispersive energy spectroscopy tests and mercury intrusion porosimetry, respectively. The latter were performed before and after carbonation. It was found that the greatest advance of the carbonation front measured with phenolphthalein is achieved under exposition conditions of 60% of CO2 and 75% of RH. The increase of the number of freeze-thaw cycles provides a higher degradation on the test samples, leading to critical carbonated depths. With 16 and 20 freeze-thaw cycles, the carbonated depth obtained on test samples matured in lab is around twice the carbonated depth tested on standard test samples. For the same number of cycles, the sample tests matured in natural conditions carbonate at 100%. Thus, it is possible to affirm that the accelerated carbonation test device developed make it possible to access the effects of carbonation and freeze-thaw in concrete with precision.
The interaction between the reinforced concrete structures and the aggressiveness of the environment, when different actions occur simultaneously, provides their early degradation. Thus, their durability is put in jeopardy and the operating time for which they were designed is reduced. Between the several mechanisms of concrete deterioration, carbonation and freeze-thaw cycles were object of study of this work. The isolated or joint action of these mechanisms causes irreversible damages in the concrete structures, with serious consequences on their stability and safety. To assess the behavior of the concrete in relation to carbonation and freeze-thaw cycles, an accelerated carbonation test device was developed where cylindrical test samples with different maturing conditions, in lab and under natural exposition conditions, are submitted to high concentrations of CO2 and different relative humidity. The accelerated carbonation tests were focused on standard test samples deteriorated by the action of successive freeze-thaw cycles. In the standard test samples have been used concentrations of 15, 30 and 60% of CO2 and the relative humidity had a variation between 32, 60, 75 and 90%. The test samples deteriorated by the action of 8, 12, 16 and 20 freeze-thaw cycles were submitted to the accelerated carbonation test under 60% of CO2 and 75% of RH. Standard concrete characterization complementary tests were also performed in relation to its durability through capillary and compressive strength absorption tests, microstructure and chemical composition through dispersive energy spectroscopy tests and mercury intrusion porosimetry, respectively. The latter were performed before and after carbonation. It was found that the greatest advance of the carbonation front measured with phenolphthalein is achieved under exposition conditions of 60% of CO2 and 75% of RH. The increase of the number of freeze-thaw cycles provides a higher degradation on the test samples, leading to critical carbonated depths. With 16 and 20 freeze-thaw cycles, the carbonated depth obtained on test samples matured in lab is around twice the carbonated depth tested on standard test samples. For the same number of cycles, the sample tests matured in natural conditions carbonate at 100%. Thus, it is possible to affirm that the accelerated carbonation test device developed make it possible to access the effects of carbonation and freeze-thaw in concrete with precision.
Description
Keywords
Carbonatação Ciclos Gelo-Degelo Durabilidade Ensaio Acelerado de Carbonatação