Critical review of standardized test methods for determining the carbonation resistance of concrete

Principal part. The article considers the recommendations on preliminary preparation and curing of specimens given in the existing domestic and foreign standards of concrete carbonization tests. The conditions of exposure to accelerated carbonization affect the mechanism of processes and the degree of changes that the material will experience. The concept of “maturity index” should be prioritized in future iterations of standards. There is a need to provide direct comparison of the results of different studies and to improve the understanding of how the internal properties of individual concrete types relate to their resistance to carbonation, to define principles for accurately translating carbonation rates in accelerated tests into natural carbonation rates for different types of concrete. Prescriptive and performance-based approaches to durability design of reinforced concrete structures are reviewed in this article. Often a direct correlation between carbonization ratio and compressive strength in concretes with mineral additives is not revealed, especially when the performance characteristics are determined by accelerated tests. Therefore, models of degradation of such concretes under the influence of carbon dioxide in semi-probabilistic, probabilistic calculations, and service life assessment need some refinement.

Conclusions. The existing standards for carbonation depth determination have significant differences from each other, in particular in the variants of specimen preparation, curing conditions, conditions during testing in the carbonation chamber. This leads to different results when tested to different standards. The performance-based approach to assessing the durability and service life of reinforced concrete structures can be considered an important advancement in structural concrete design. At present, the limitations in this approach are due to the fact that the various failure processes affecting the behavior of reinforced concrete structures are not fully studied and described in all necessary details, laboratory test methods do not always reflect the actual operating conditions, and the variation of concrete quality within a structure are determined by the heterogeneity and anisotropy of properties, the presence of defects, time-dependent parameters (shrinkage, creep), and other probabilistic factors.

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