Publicação
Durabilidade do betão à ação combinada da carbonatação e dos iões cloreto considerando a presença de cinzas volantes
| Resumo: | To ensure the durability of concrete structures it is necessary to understand its behaviour in the presence of aggressive agents. Carbonation and chloride ingress are the two main causes of degradation in reinforced concrete. Despite the combined action of these two mechanisms being a reality, the few research endeavours on the area have not yet reached a consensus on the effect of the combined action of chlorides and carbonation on the durability of concrete. The fly ash content of the concrete is another important point in the studied, since the concrete with fly ash presents different behaviour in relation to the penetration of chlorides and the action of carbonation. To contribute to this ongoing and important discussion, laboratory tests were carried out to evaluate the influence of carbonation on the penetration of chlorides, the influence of the presence of chlorides on the carbonation front, the influence of the fly ash in this context and the influence of the type of test in the results. Moreover, this work also contributes to the discussion on the use of the immersion and drying cycles. Concrete specimens were cast with different water cement ratios: 0,40, 0,50, 0,55 and 0,60. Mortar and cement past were cast too. Specimens with 40% replacement of cement for fly ash (by mass) were molded. For mortar, specimens with 20 and 60% replacement of cement for fly ash were also molded. In addition, the following accelerated tests were used: carbonation chamber (T = 20ºC, HR = 60%, CO2 = 4%), chloride migration test, chloride diffusion by immersion (3,50% NaCl) and immersion and drying test. The time of exposure to the aggressive agents, combined or not, was also evaluated. According the results, the presence of chloride ions leads to a reduction in the carbonation depth. However, the chloride penetration into the cementitious matrix seems to be related to the carbonation depth. Regardless of the accelerated test used, from a certain carbonation depth, in this case identified as 8,00 mm, the carbonation increases the chloride penetration. On the other hand, for very low carbonation depths, below 8,00 mm, the carbonation decreases the chloride penetration. Regarding the use of fly ash in the cementitious matrix studied, it is possible to verify a significant increase in the chloride penetration in these matrices. As a consequence, there is a significant reduction in the chloride penetration resistance in concrete with fly ash. Regarding the type of test used to combine the chloride penetration and carbonation, it is possible to say that the combination of the carbonation chamber with the chloride diffusion by immersion seems to be the most appropriate choice for this study. |
|---|---|
| Autores principais: | Malheiro, Raphaele Lira Meireles Castro |
| Assunto: | Engenharia e Tecnologia::Engenharia Civil |
| Ano: | 2018 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | português |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | To ensure the durability of concrete structures it is necessary to understand its behaviour in the presence of aggressive agents. Carbonation and chloride ingress are the two main causes of degradation in reinforced concrete. Despite the combined action of these two mechanisms being a reality, the few research endeavours on the area have not yet reached a consensus on the effect of the combined action of chlorides and carbonation on the durability of concrete. The fly ash content of the concrete is another important point in the studied, since the concrete with fly ash presents different behaviour in relation to the penetration of chlorides and the action of carbonation. To contribute to this ongoing and important discussion, laboratory tests were carried out to evaluate the influence of carbonation on the penetration of chlorides, the influence of the presence of chlorides on the carbonation front, the influence of the fly ash in this context and the influence of the type of test in the results. Moreover, this work also contributes to the discussion on the use of the immersion and drying cycles. Concrete specimens were cast with different water cement ratios: 0,40, 0,50, 0,55 and 0,60. Mortar and cement past were cast too. Specimens with 40% replacement of cement for fly ash (by mass) were molded. For mortar, specimens with 20 and 60% replacement of cement for fly ash were also molded. In addition, the following accelerated tests were used: carbonation chamber (T = 20ºC, HR = 60%, CO2 = 4%), chloride migration test, chloride diffusion by immersion (3,50% NaCl) and immersion and drying test. The time of exposure to the aggressive agents, combined or not, was also evaluated. According the results, the presence of chloride ions leads to a reduction in the carbonation depth. However, the chloride penetration into the cementitious matrix seems to be related to the carbonation depth. Regardless of the accelerated test used, from a certain carbonation depth, in this case identified as 8,00 mm, the carbonation increases the chloride penetration. On the other hand, for very low carbonation depths, below 8,00 mm, the carbonation decreases the chloride penetration. Regarding the use of fly ash in the cementitious matrix studied, it is possible to verify a significant increase in the chloride penetration in these matrices. As a consequence, there is a significant reduction in the chloride penetration resistance in concrete with fly ash. Regarding the type of test used to combine the chloride penetration and carbonation, it is possible to say that the combination of the carbonation chamber with the chloride diffusion by immersion seems to be the most appropriate choice for this study. |
|---|