A Critical Review of Existing Test-Methods for External Sulfate Attack

Abstract

External sulfate attack (ESA) of cementitious materials has been studied worldwide for a very long time. This physical/chemical interaction between sulfate ions and the cement hardened elements affects the long-term durability of concrete structures: cracking, spalling or strength loss of concrete structures. To study these damaging phenomena, some standardized and non-standardized accelerated aging tests are used to evaluate the performance of cements in sulfate-rich environments. However, these existing methods do not adequately predict field performance and some shortcomings or deficiencies still exist: change of degradation mechanisms when using high concentrations of sulfate, variable boundary conditions and small specimens compared to the real concrete structures. In this work, a critical review of some existing test methods and foreign national standard methods for ESA are presented, analyzed, and discussed. This results in some proposed recommendations for improving these methods to meet the needs of structure managers.

Chemical Mechanisms Involved in the Coupled Attack of Sulfate and Chloride Ions on Low-Carbon Cementitious Materials: An In-Depth Study

“…However, after 25 days of exposure, an increase in total porosity was observed in the four mixes. This was attributed to the excessive formation of expansive products that led to expansion and cracking, as well as the dissolution of CH, decalcification of C-S-H, and consumption of AFm that led to an increase in porosity, although hydration was still in process [12,18,61]. These results are in accordance with the chemical investigations explained in previous sections.…”

“…These products are primarily responsible for concrete expansion and cracking. The formation of these chemical compounds induces internal pressure within the concrete matrix, leading to structural deterioration and compromising its long-term integrity [12][13][14]. Nevertheless, unbound chloride ions within the cement matrix, such as Friedel's salt, remain free and contribute to the corrosion of steel reinforcing bars (rebars).…”

New Methods for Assessing External Sulfate Attack on Cement-Based Specimens

“…This result confirms that ESA-induced expansion can be accurately monitored with OF sensors. Due to the deterioration of the optical fiber, the exposure lasted for only 78 days, which is a sufficient duration for some test methods, such as Swiss standard SN 505262-3 [46]. This suggests that future studies should continue this experimental work by testing other types of OF.…”

Long-Term Effects of External Sulfate Attack on Low-Carbon Cementitious Materials at Early Age

“…However, each method comes with its strengths and limits, and many are criticized for their dissimilarity with respect to real-world field exposure conditions. Notably, various testing standards, such as ASTM C 1012, the Asian method, the Swiss method, and CSA A 3004-C8, employ high concentrations of sodium sulfate (greater than 30 g/L) [18] to generate an infinite source of sulfate and accelerate the test. A study conducted by Biczok [19] revealed that the preferential formation of ettringite occurs when a low concentration of sulfate is selected, while higher sulfate concentrations lead to an increased production of gypsum.…”