Abstract
Understanding the performance of concrete in the marine environment is significant for preventing the corrosion of chloride ion for marine buildings. In this study, the uniaxial compressive strength (UCS), chloride ion concentration (CIC), microstructure, and pore structure of admixture concretes were tested to study the mechanical properties and microscopic characteristics under the single marine corrosion, the single freezing-thawing, and the coupled marine corrosion and freezing-thawing conditions. The results indicate that the concrete mixed with both fly ash and mineral powder has better UCS, chloride ion penetration resistance, and freezing-thawing resistance than the concrete with the single fly ash or mineral powder. Under the marine corrosion environment and coupled corrosion and freezing-thawing environment, the UCS of the concrete with both fly ash and mineral powder increases firstly and then decreases with the increase of the corrosion time. This is because the pore of the filling body is filled by large crystalline salts generated by the reaction of chloride ions and concrete; then, cementation of the cement is increased in the early corrosion; meanwhile, the increase of crystal salt in the subsequent corrosion process leads to the growth of microcracks and the formation of macrocracks in concrete specimens. In addition, a freezing-thawing-corrosion composite strength impact factor is introduced to describe the effect of coupled corrosion and freezing-thawing on the mechanical property of the concrete. The results show that the corrosion is the dominant factor after 0, 30, and 60 freezing-thawing cycles, while the freezing-thawing is the dominant factor after 90 freezing-thawing cycles.
Highlights
At present, concrete is the most widely used building material due to its low price, simple production process, high compressive strength, and durability [1,2,3]
The durability of concrete structures in sea beaches is always affected by multiple environmental factors [13], while concrete structures in deep underground engineering may be affected by complex in situ stress and sulfate corrosion [14], and concrete structures in the cold areas suffer from freezing-thawing condition [15]
Experiments on concretes have shown that the strength of concrete decreases with the increase of freezingthawing cycles [27, 28]. erefore, the methods of concrete resistance to freezing-thawing have been studied by scholars, and the results indicated that adding fly ash and mineral powder in concrete can resist the freezing-thawing environment [29, 30]
Summary
Concrete is the most widely used building material due to its low price, simple production process, high compressive strength, and durability [1,2,3]. The durability of concrete structures in sea beaches is always affected by multiple environmental factors (e.g., humidity, freezing-thawing, and chloride ion corrosion) [13], while concrete structures in deep underground engineering may be affected by complex in situ stress and sulfate corrosion [14], and concrete structures in the cold areas (e.g., northeast and northwest China) suffer from freezing-thawing condition [15]. Different methods have been proposed to improve the durability of concrete in the marine corrosion environment, such as changing the water-binder ratio [18] and the water-cement ratio [19], trying different types of cement [20], and adding admixture (e.g., fly ash and mineral powder) [21]. The transportation mechanism of chloride ion in concrete [22] and life cycle of concrete in marine corrosion environment have been widely investigated [23]
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