Volume 22, Issue 2 (2022)                   MCEJ 2022, 22(2): 177-194 | Back to browse issues page

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samimi K, pakan M. Evaluation of chloride ion penetration in fibrous concretes containing metakaolin and pumice under immersion and tidal conditions. MCEJ 2022; 22 (2) :177-194
URL: http://mcej.modares.ac.ir/article-16-55347-en.html
1- Assistant Professor, Faculty of Civil, Water and Environmental Engineering, Shahid Beheshti University, Tehran, Iran , K_samimi@sbu.ac.ir
2- PhD Student, Faculty of Civil, Water and Environmental Engineering, Shahid Beheshti University, Tehran, Iran
Abstract:   (914 Views)
In the past, fiber reinforced concretes (FRC) was used mainly in pavements and industrial floors however, FRC has a number of other uses as well, with recent uses including bridges, hydraulic structures, tunnels, pipes, canal linings and safety vaults. On the other hand, the resistance of FRC against to penetration of chloride ions, especially bonded chloride, has received less attention. In addition, the prior literature's results on chloride ions bound in different concretes have always been varied. This study analyses the mechanical characteristics of fibrous and normal concretes (NC) containing two pozzolans of metakaolin and pumice using microstructural investigation. Also, the chloride isothermal under marine environment was studied by simulating the immersion and tidal conditions. This study can be beneficial for use in different applications such as paving and bridges which are under the influence of chloride ion penetration. The first goal of this study is to increase the flexural strength of the pavement layer in order to reduce its thickness which can be economical, and the second goal is to study the durability performance of NC and FRC containing of cementitious material (pumice and metakaolin) with respect to the aggressive medium that is a determining factor in the lifetime of concrete structures. It is generally acknowledged that blocking the paths of chloride penetration by densifying the microstructures of the concrete can be a fundamental solution using pozzolanic reaction produced by pozzolans to enhance the durability of concrete. In the last years, metakaolin and pumice has been introduced as a highly active and effective pozzolan for the partial replacement of cement in concrete. Metakaolin and pumice consumes the Ca(OH)2 that is produced from the cement hydration process rapidly and effectively and in addition to CSH, phases like C2ASH8 (stratlingite), C4AH13 and C3ASH6 (hydrogarnet) are produced. These pozzolanic products enhance the structural properties of concrete and also contribute to total pore refinement. In this study, six concrete mixtures with a control mixture without any addition are prepared and tested in hardened states. Afterwards, the resistance to chloride penetration both in immersion and tidal conditions is investigated. Accordingly, first, the compressive strength and flexural strength test were performed on hardened states to assess the mechanical resistance of the different prepared mixtures at early ages and up to 365 days. Then, the microstructure study of six prepared mixtures were investigated by using Scanning Electron Microscope (SEM), EDX spectrum and CT scan test. Finally, the chloride penetration resistance of the different concrete mixtures was evaluated by measuring water-soluble chloride profile, bonding and total chloride in immersion and tidal conditions. In both the immersion and the tidal conditions, durability results show that metakaolin and pumice have a significant effect on the increasing chloride penetration resistance. This impact was far more apparent in pumice-containing samples. However, the concretes containing pozzolans have a porous structure, according to computed tomography scan (CT scan) analysis and microstructure results in this study, and the Ca / Si ratio is considerably lowered owing to decalcification. Also, the results showed that despite the structural porosity in concretes containing pozzolans, factors such as Ca / Si ratio and pore solution concentration play a very important role in their durability against chloride ion in the simulated marine environment.
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Article Type: Original Research | Subject: Civil and Structural Engineering
Received: 2021/09/3 | Accepted: 2022/02/22 | Published: 2022/05/31

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