Rationale

Ballot Action: Revise ASTM C688 Standard Specification for Functional Additions for Use in Hydraulic Cements to remove the C151 autoclave expansion test requirement. Rationale: ASTM Committee C01 in 2022 removed the C151/C151M autoclave expansion test (AET) requirement from ASTM C150/C150M Specification for Portland Cement, and AASHTO Committee on Materials and Pavements (COMP) and the parallel AET, AASHTO T 107, from AASHTO M 85 Standard Specification for Portland Cement. Other standards where C151/C151 M were also removed include ASTM C465 Specification for Processing Additions for Use in the Manufacture of Hydraulic Cements, C595/C595M, C618 and others. CSA A 3000-18 (2021 amendment) has removed the autoclave expansion test method and cementitious materials AET requirements with no replacement. Background and reasons for the removal of C151 from C150 are provided in the C01 (21-01) Ballot Item #1 rationale, which is posted on the ASTM C01 “Closed Ballots and Closing Reports” webpage. Numerous references on the topic are cited in the rationale and in the referenced report by Kabir and Hooton (2020). Similarly, the rationale supporting removal of the C151/C151M requirement from ASTM C465 can be viewed on the ASTM C01 “Closed Ballots and Closing Reports” webpage. The referenced report by Shkolnik (2020) provides a literature review on the use of the autoclave expansion test for fly ashes. To summarize, concern about delayed expansion due to MgO (periclase) in cement was prompted by some high profile concrete expansion failures in the late 1800’s and early 1900’s. These cements contained high MgO in the range of 16 to 30% compared to the current C150/C150M 6% maximum. In the 1920’s some field failures were attributed to excess free lime (CaOfree) coming from the portland cement. The autoclave expansion test was developed as an accelerated method that would provide an index of potential delayed expansion of a cement paste caused by the hydration of CaO, MgO, or both under the C151/C151M. However, the usefulness of the autoclave expansion test has been controversial and it has not been widely adopted in standards outside of North America. Concerns are articulated in published reports: • No correlation has ever been shown between the autoclave test specification limits and soundness of concrete (Mehta 1978). • No concrete failures have been attributed to cements failing soundness testing or containing high amounts of MgO in over 60 years (Klemm 2005). • Similarly, in countries where the autoclave test is not required, there have been no reported cases of MgO-related soundness failures (Klemm 2005). • The AET appears to be overly harsh, and the strength of the pastes at one day are too weak to resist the extremely rapid volume changes induced by the AET (Tazawa et al. 2000; Kabir et al. 2020). • While free lime (CaOfree) can contribute to autoclave expansion, free lime is intrinsically more reactive than periclase. Additionally, higher free lime cements or hard-burned free lime in cement are not commonly found in modern day cements due to better efficiencies and process controls in cement plants (Kabir and Hooton 2020). • ASTM C183 permits retesting cement and CaO-related expansions in the autoclave test tend to go away. Hooton (2021) provided data from a cement plant whose cement have no history of field expansion, but periodically did not meet ASTM C151 limits on first testing. After waiting two weeks in a sealed bucket, upon retesting, the autoclave expansions were reduced and well within limits. Given these findings and considerations, this proposal would remove the ASTM C151/C151M autoclave expansion limits from C688 Specification for Processing Additions for Use in the Manufacture of Hydraulic Cements.