Abstract
The main purpose of this study is to determine the metakaolin (MK) impacts on the concrete durability when the concrete is subjected to joint corrosion of SO42−,Mg2+ and, Cl−. Four groups of concrete test samples, which contained different MK contents, were designed and tested in order to see their physical property changes and macro-morphology differences during the cyclic corrosion process. And a series of approaches, including XRD, FTIR, SEM, and EDS, were applied to study the concrete phase composition changes and the micro-morphology features of all groups. According to the test results, when reaching 20 cycles, the concrete sample with 10% MK showed the best concrete physical properties; when reaching 120 cycles, the concrete with 5% MK content showed the best durability, produced similar amount of corrosion products to ordinary concrete, and presented relatively compacted micro-structure and small internal porosity. Mg2+ actually has a great impact on metakaolin. The corrosion product quantity increased significantly when MK admixture reached 15%. Due to the great number of produced M-S-H, the corrosive ions damaged the concrete for a second time, leading to serious aggregate peeling-off, powder surface of test samples, and porous micro-structure.
Highlights
With the rapid development of economy and continuous improvement of industrialization, large infrastructures, such as high-rise buildings, large bridges, and tunnels, have been constructed one after another
Since the key study objects of this paper are the concretes that are added with different volumes of metakaolin, in order to show the differences among various groups of concrete samples obviously, the macro test, X-ray diffraction (XRD) test, and Fourier transform infrared spectrum (FTIR) test were carried out when reaching the most representative “120 cycles”
The trend of relative compressive strength changes of the concrete added with metakaolin is: rising stage →flat stage→declining stage→rapid declining stage
Summary
With the rapid development of economy and continuous improvement of industrialization, large infrastructures, such as high-rise buildings, large bridges, and tunnels, have been constructed one after another. For the reduction of greenhouse gas emission of the cement industry around the world, the most effective way is to minimize the cement use (Environment et al, 2018), which can be achieved by replacing certain proportion of cement by mineral admixture Both the coal fly ash and blast furnace slag are the commonly used mineral admixtures (Supit and Shaikh, 2014; Juenger and Siddique, 2015; Hemalatha and Ramaswamy, 2017), but for common coal fly ash, though it can effectively reduce cement dosage and lower the economic cost, it has adverse effect on concrete performance at initial stage due to its low activity and large particle size (Jiang, 2005). The metakaolin can improve the mechanical properties of the concrete at the initial stage (Chen et al, 2021a), which perfectly solve the adverse effects brought by traditional mineral admixture (ordinary coal fly ash and blast furnace slag) to the concrete
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