Developing New and Optimizing Current Test Methods to Evaluate Sulphide-bearing Aggregate

Abstract

This research focuses on testing the applicability on aggregates from Ontario of a testing protocol to evaluate the potential oxidation of sulphide-bearing aggregates, optimizing the protocol test methods, and develop new tests based on the obtained results. The protocol comprises of three sequential tests: Total sulphur content, Oxygen Consumption Test and Oxidation Mortar Bar Test. For the oxygen consumption test, using processing equipment with cast iron media, was found to contaminate the samples and produce high consumption. Moreover, controlling the tested aggregate gradation produces higher consumption and more consistent results than using a fine aggregate sample (<150µm) without controlling the minimum size. The oxidation consumption test showed lower expansion values for carbonate aggregates compared to aggregates with high silicate content. Exposing siliceous aggregate, whether alkali-silica reactive or not, to the high pH from the oxidizing solution and the high temperature produces high expansion regardless of the oxidizable sulphide content. As such, new expansion criteria are suggested which takes into consideration the silicate content of the aggregates. The dissertation proposes, based on testing twenty-six aggregates, modifications to: the oxygen consumption test; the expansion criteria of the mortar bar test; and proposes a new oxidation mortar bar test to avoid the limitation of the applicability of the original mortar bar test on siliceous aggregates. In the new testing program, different testing regimes were investigated using different oxidizing agents and environmental conditions that can promote oxidation of sulphide-bearing aggregates, without the promotion of other chemical reactions (Alkali silica reaction products or Friedel’s’ salt). Out of the various investigated tested regimes, two testing procedures showed promising results and recommended for further development and use. Bleach and lime water are used in these tests as the oxidizing agents; however, mortar bars in both regimes are stored at lower temperature compared to that of the original test in the protocol. Based on the expansion results, new expansion criteria are suggested that can detect if the aggregate contains oxidizable sulphides.

Development of a Sulfide-Bearing Aggregate Oxidation Test in Concrete

“…MSK with high sulfur content did not pass the OCT optimized by El-Mosallamy and Shehata (2020b) and OMBT portion of the protocol proposed by Rodrigues, et al (2016), while MSK with low sulfur content passes the OCT portion of the protocol and is under OMBT investigation, the results of which will be discussed in the next section. Mosallamy, 2019; as expected, while 1049 fails although it is very closed to the limit for OCT, which is explained by high abrasion resistance and higher contamination of the samples by oxidizable material in the grinding machinery components according to El-Mosallamy and Shehata (2020b). 1049 was used in concrete mixes discussed in…”

“…vi Figure 2-2 Gypsum formation found in concrete core from deteriorated building foundation due to ISA (Rodrigues A. , et al, 2012) Trois-Riviere, Quebec Canada (Rodrigues A. , et al, 2012) Figure 2-15 Sulfide-bearing aggregate evaluation protocol ............ (Shi, Wang, & Behnood, 2012;Crammond, 2003;Rahman & Bassuoni, 2014;Rodrigues A. , et al, 2012) The foundations had to be replaced and the federal and provincial governments had to set aside millions of dollars of financial aid for the community (Rodrigues A. , et al, 2012;El-Mosallamy, 2019).…”

“…SEF is expansive and can cause cracking, spalling and pop outs in concrete. (Cheng, Huang, Yuan, & Deng, 2020;Rahman & Bassuoni, 2014;El-Mosallamy, 2019;Xu, 2013;Tagnit-Hamou, Saric-Coric, & Rivard, 2005).…”

“…There is evidence that suggests thaumasite forms only at pH above 10.5, below which thaumasite decomposed into popcorn calcite, making concrete one of the environments where most conditions are met. Thaumasite formation attacks the CSH gel leaving behind a noncohesive, pulpy mass containing aggregate particles residues, making TSA a much more severe form of sulfate attack (Cheng, Huang, Yuan, & Deng, 2020;Mittermayr, et al, 2013;Nielsen, Nicolai, Darimont, & Kestemont, 2014;El-Mosallamy, 2019;Rahman & Bassuoni, 2014;Shi, Wang, & Behnood, 2012).…”

“…The effect of Metakaolin is controversial. Depending on the amount of sulfate ions present in the pore solution it could prevent or favor expansion (El-Mosallamy, 2019;Xu, 2013;Al-Akhras, 2006). In the case of concrete samples with metakaolin in Figure 4-7 and Figure 4-8 the absence of expansion is most likely due to the reason given for all the other samples and not due to the presence of metakaolin.…”