ASTM/AASHTO Harmonization

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AASHTO M 85 and ASTM C150 Portland Cement Specifications to be Harmonized

The American Association of State Highway and Transportation Officials’ (AASHTO) Subcommittee on Materials and ASTM International’s Committee C01 on Cement recently passed ballot proposals to harmonize remaining significant differences between the provisions of the standard specifications for portland cement, AASHTO M 85 and ASTM C150. The 2009 editions of the standards are anticipated to be available in late July. With the following changes, all of the specification requirements for both ASTM C150 and AASHTO M 85 will be the same:

AASHTO M 85 and ASTM C150 have existed as parallel standards for portland cement since the 1940s, and US state departments of transportation reference either AASHTO M 85 or ASTM C150 when specifying portland cement for concrete construction. Currently, out of 51 state departments of transportation (including Washington, DC), 31 reference AASHTO M 85, 16 reference ASTM C150 and four reference both.

While the provisions of AASHTO M 85 and ASTM C150 have generally been consistent, there have also been some substantive differences. However, there are important benefits in having consistent requirements in the two specifications. Benefits to users and owners include having portland cement standards that meet product application needs and not having to worry about whether an “ASTM cement” was used when an “AASHTO cement” should have been used. Thus, user specification and quality assurance is simplified. For the concrete producer, the need to maintain different silos and/or sourcing for state highway projects is eliminated. For the cement producer, harmonization eliminates the need for special production runs and storage requirements. Improved consistency can be expected from simplified quality control. The net effect is better quality concrete!

Consistent Provisions that Meet Collective Needs

Recognizing that the number of significant differences between the standards was growing and realizing the benefits of harmonization, AASHTO Subcommittee on Materials Technical Section 3a on Hydraulic Cement and Pozzolanic Materials (AASHTO SOM TS3a) and ASTM Committee C01 on Cement (ASTM C01) established a Joint AASHTO-ASTM Harmonization Task Group (JAAHTG) in the fall of 2003 to examine significant technical differences between the standards and develop recommendations for having consistent requirements that meet the needs of AASHTO and ASTM members. Task group members agreed that to meet collective needs a standard cement specification should:

1. Ensure concrete performance (recognizing that cement is only part of the concrete performance equation);
2. Provide means of determining compliance;
3. Provide a consistent material;
4. Use simple, reliable testing and sampling methods;
5. Provide flexibility for optimization of available natural resources and manufacturing technology, and accommodate various user requirements; and
6. Ensure understandable communication between buyer and seller.

Discussion revealed differences in the relative value various task group members placed on these standardization attributes and differences in opinions held about the contribution of specific standards provisions toward meeting these expectations, but there was and continues to be a consensus that each of these expectations stems from valid user, producer, and general interest standardization needs.

From this foundation, the task group proceeded to examine a total of five significant differences over the last six years. Task group members carefully considered reasons for differences, evaluated the purpose of provisions, explored alternate ways of achieving that purpose, and collaboratively identified harmonization solutions that work for everyone. That approach resulted in recommending significant changes to both AASHTO M85 and ASTM C150 such that the revised standards enable more efficient use of natural resources and cement manufacturing technology, while ensuring a basis for improved quality of concrete construction. In doing so, they strengthen the sustainable development attributes of concrete construction.

The first series of changes recommended by the Joint AASHTO-ASTM Harmonization Task Group was adopted in the 2007 editions of AASTHO M85 and ASTM C150 (see CTEC February 2007 article “AASHTO and ASTM Take Three Giant Steps toward Harmonizing Standards for Portland Cement” ), when the standards incorporated consistent provisions for fineness, Type II C3S content, heat of hydration–related criteria, and use of up to 5% limestone in portland cement. The most recent set of 2009 changes includes resolution of remaining differences between the standards and refinements to other existing provisions of the standards.

Detailed Changes to AASHTO and ASTM Portland Cement Standards

Footnote D of Table 1 in both specifications (prior to 2009) noted that performance of portland cements could sometimes be improved with higher SO₃ contents than the default limits listed in the table, referring to C563 somewhat ambiguously as a means of demonstrating that fact and referring to C1038 data to be made available upon request to demonstrate that a cement was not oversulfated. However, it is well accepted that “optimum” sulfate contents for some applications are different than the approximate optimum determined using strengths of ASTM C563 mortars for a variety of reasons (mixing intensity used, presence of supplementary cementitious materials or chemical admixtures, field temperatures, and other performance indicators besides strength, to name a few).

A source of confusion was the fact that within ASTM and AASHTO standards footnotes to tables are mandatory, while the previous footnote included both informational language and mandatory requirements. Therefore, the footnote was sometimes interpreted as requiring that the sulfate content of a cement not exceed the optimum determined by ASTM C563 testing while others believed the text referenced ASTM C563 as an example of a method of optimizing sulfate content, but did not exclude consideration of other performance aspects of the cement, provided the C1038 criteria are met. The new revision removes the informational first sentence of the previous footnote, while making clear a requirement to report C1038 data routinely, rather than upon request.

Existing (pre-2009) fineness requirements of the standards include limits on single samples and average values of 5 consecutive samples; however, the word “sample” has various meanings: A cement producer takes multiple “samples” per day for production control testing and may obtain them from several locations during production. “Samples” may also refer to daily, weekly, or monthly composites, units of shipment, or lots of different sizes. Cement may be sampled from a variety of different points in the transportation process: at the manufacturing plant, at the construction site, or at an intermediate storage facility. Each of these “samples” represents different snapshots, making comparisons of the data questionable. Again after considering multiple options, the JAAHTG concluded that moving to single maximum and minimum fineness limits provides the best solution by providing the clearest requirements. Minimum fineness limits of 260 _m2/kg (Blaine) or 150 m₂/kg (Wagner) for Types I, II, II(MH), IV, and V have been implemented and maximum limits of 430 m₂/kg (Blaine) or 245 m₂/kg (Wagner) for Types II(MH) and IV.

A new Type II(MH) cement was developed in response to several comments on ballots of previous harmonization proposals. These noted a need by some users for a moderate sulfate resistant cement not subject to heat of hydration-related criteria. Examples of concrete applications for such cements include precast members or general residential construction that might require moderate sulfate resistance without strength development restrictions associated with moderate heat provisions. As a result, JAAHTG members evaluated several alternatives for achieving cement type designations addressing sulfate resistance without criteria intended to limit heat of hydration.

Their final recommendation was that Type II designate a moderate sulfate resistant (only) cement, with no maximum fineness, heat index, or C186 test requirements. A new Type II(MH), designated for moderate heat of hydration and moderate sulfate resistance, would include those requirements. Options for an air-entraining version, Type II(MH)A are also included. The new cement types must meet a chemical requirement for heat of hydration (“heat index”) of C₃S+4.75C₃A=100, and have maximum fineness requirement of 430 m₂/kg (Blaine), in addition to meeting other chemical and physical requirements for Type II cements. An exception for the maximum fineness requirements is made if the heat index is less than or equal to 90.

Probably the most significant recent change to these specifications has to do with Processing Additions Requirements. Processing additions are materials interground to aid in the manufacture or handling, or both, of a portland cement. Previously, processing additions were limited to 1% by mass in M 85 and both C150 and M 85 required qualification of processing additions by ASTM C465. None of these specifications distinguished between requirements for organic and inorganic processing additions. While the first processing additions used in portland cement were organic grinding aids, inorganic processing additions, such as granulated blast furnace slag and fly ash, have since been used in the manufacture of portland cements to improve efficiency of manufacturing. Based on this situation and questions regarding effects of such additions on cement and concrete properties, a research project was sponsored by the National Cooperative Highway Research Program (NCHRP) to evaluate the effects of processing additions on portland cements. This project was completed in January 2008 (Taylor 2008) and JAAHTG members reviewed the report and developed their proposals based on its findings.

Traditional organic processing additions can be used in amounts up to 1% by mass and need to meet the requirements of ASTM C465 in the amounts used or greater. Inorganic processing additions can also be used in amounts of up to 5%. Since the use of inorganic processing additions (IPAs) in amounts of less than 1% was not observed to influence performance of cementitious systems to a significant extent in any test in the NCHRP study, no additional testing beyond that already indicated by the specification is required for use of IPAs at up to 1%. If inorganic processing additions are used in amounts greater than 1%, testing of the cementitious system is required in accordance with the protocols in ASTM C465. Changes to ASTM C465 distinguish between requirements for organic and inorganic processing additions. A new AASHTO specification, M 327, was simultaneously developed with identical provisions to the revised ASTM C465.

Finally, the mandatory annexes of C150 and M 85 were both revised to update Bogue potential phase composition calculations. Many inorganic processing additions, even at the low levels used in portland cements, can lead to chemical analyses that cause significant changes to the Bogue calculations. Although the Bogue calculations only provide estimates of phase composition, procedures for adjusting the calculations to correct these values were developed. As part of these revisions, inorganic processing additions analyses are reported, along with Bogue phase compositions of the base cements.

All of the changes developed through the harmonization effort are summarized in the table below.

This effort to improve the specifications will continue as AASHTO and ASTM address new business items resulting from the balloting process in both organizations, advances in cement and concrete technology, and marketplace needs.

References

Taylor, P., Specifications and Protocols for Acceptance Tests on Processing Additions in Cement Manufacturing, NCHRP 607, Transportation Research Board, Washington, D.C., 2008, 96 pages. Accessed (May 1, 2009)

For the most recent editions of the specifications, please visit the following websites:

AASHTO: https://bookstore.transportation.org/

ASTM: http://www.astm.org/Standards/C150.htm

 
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