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AASHTO and ASTM Take Three Giant Steps
toward Harmonizing Standards for Portland Cement
 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
three of five significant differences between the provisions of
the standard specifications for portland cement, AASHTO M 85 and
ASTM C 150, published by these organizations. As a result, the 2007
editions of these standards will have consistent provisions for
fineness, Type II C3S content, heat of hydration–related
criteria, and use of up to 5% limestone in portland cement. It is
anticipated that revised standards will be published in July of
2007.
Currently, five significant differences exist between the two specifications:
- AASHTO M 85 has maximum fineness (Blaine and Wagner) limits
- AASHTO M 85 has a maximum limit of 58 % tricalcium silicate
(C3S) for Types II and IIA
- AASHTO M 85 has a 1% processing additions limit
- ASTM C 150 now provides for use of up to 5% limestone
- ASTM C 150 has removed the minimum 20% SiO2 limit
for Type II cement
The 2007 editions of AASHTO M 85 and ASTM C 150 will have maximum
average and single sample Blaine fineness limits for Type II and
Type IV cements of 420 m2/kg and 430 m2/kg,
respectively. The two standards will not have a maximum tricalcium
silicate (C3S) limit for Type II cement, but will require
Type II cement to meet the following heat index equation:
C3S + 4.75C3A ≤ 100
For informational purposes, ASTM C 186 heat of hydration testing
will be required at least every six months. Finally, both standards
will have provisions for the use of up to 5% limestone in cement.
Work continues to develop harmonization proposals to address differences
in processing additions limits and Type II SiO2 limits.
Background and History of Harmonization Effort
These changes are the result of an ongoing focused harmonization
effort that was initiated in the summer of 2003. AASHTO M 85 and
ASTM C 150 have existed as parallel standards for portland cement
since the 1940s, and US state departments of transportation reference
either AASHTO M 85 or ASTM C 150 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 C 150 and four reference both.
 While
the provisions of AASHTO M 85 and ASTM C 150 have generally been
consistent, there have also been some substantive differences, and,
prior to this harmonization effort, the number of differences seemed
to be increasing. However, there are important benefits to users
and producers 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 would be simplified. For the concrete producer,
the need to maintain different silo and/or sourcing for state highway
projects would be eliminated. Quality control for concrete would
be simplified, resulting in a more consistent product. Working with
a similar product for a given type designation would enable the
producer to better predict the performance of the concrete and the
compatibility with other ingredients. For the cement producer, harmonization
would eliminate the need for special production runs and storage
requirements. Improved consistency could be expected from simplified
quality control. The net effect would be better quality concrete!
Recognizing 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)
consisting of four members each from AASHTO TS3a and ASTM C01. Since
November 2003, the JAAHTG has met monthly or bi-monthly either by
conference phone, web conference, or in-person to consider existing
significant differences between AASHTO M 85 and ASTM C 150 and to
develop recommendations for having equivalent requirements in these
two standards. Task group membership was later expanded to include
six representatives from each standards organization.
From the onset, task group members recognized that harmonization
would need to be a collaborative effort, requiring direct and open
communication and mutual understanding and consideration of user
and producer needs. Harmonization would likely result in changes
to both ASTM C 150 and AASHTO M 85 as a result of this collaborative
approach, and the effort would be a long-term activity, since standards
must constantly change to remain relevant to the demands of the
marketplace.
As task group members focused on developing harmonization proposals
that meet the collective needs of AASHTO members and ASTM user,
general interest, and producer members, they agreed that a cement
standard specification should:
- ensure concrete performance (recognizing that cement is only
part of the concrete performance equation)
- provide a means of determining compliance
- provide a consistent material
- use simple, reliable testing and sampling methods
- provide flexibility for optimization of available natural resources
and manufacturing technology, and accommodate various user requirements
- ensure understandable communication between buyer and seller
Discussion revealed differences in the relative value various task
group members place on these standardization attributes and differences
in opinions held about the contribution of specific standards provisions
toward meeting these expectations, but there is consensus that each
of these expectations stems from valid user, producer, and general
interest standardization needs.
From this foundation, the group proceeded to examine current differences,
consider the reasons for provisions, and collaboratively identify
harmonization solutions that work for everyone. In March of 2004
task group members agreed to focus attention on developing proposals
to harmonize the fineness and Type II C3S provisions of the standards.
Task group members proposed, discussed, balloted, and reviewed several
concepts for harmonizing the differences in fineness and C3S requirements
of the two standards.
By the end of the June 2005 task group meeting, members agreed
to forward a harmonization proposal to the appropriate ASTM and
AASHTO committees. The harmonization proposal would require changes
to both AASHTO M 85 and ASTM C 150 and result in consistent fineness
and C3S requirements. Proposed changes to fineness and C3S requirements
were linked in recognition that they address related cement and
concrete performance characteristics, especially early strength
development and attendant heat of hydration.
Changes to AASHTO and ASTM Portland Cement Standards
Harmonization of the fineness requirements would be achieved by
requiring a maximum average Blaine fineness value of 420 m2/kg and
a maximum individual value of 430 m2/kg for Type II and Type IV
cements in both AASHTO M 85 and ASTM C 150. The proposal would require
changes to ASTM C 150 to include these maximum fineness criteria
for Type II and Type IV cements. Changes to AASHTO M 85 would entail
removing the maximum fineness limits on Type I and Type V cement
and increasing the fineness limits for Type II and Type IV cements
from the existing maximum average value of 400 m2/kg and maximum
individual value of 420 m2/kg.
Harmonization of the Type II C3S requirement would be achieved
by including a mandatory provision for limiting the heat of hydration
for Type II cement in both ASTM C 150 and AASHTO M 85 consistent
with a 7-day heat of hydration value of 80 cal/g by meeting the
equation:
C3S + 4.75C3A ≤ 100 (Equation 1)
Changes to AASHTO M 85 Type II cement would entail replacement
of the existing mandatory 58% limit on C3S and the optional
requirements for the sum of C3S + C3A with
a mandatory requirement to meet Equation 1. Changes to ASTM C 150
Type II cement would entail removal of the optional requirements
for the sum of C3S + C3A, and addition of
the requirement to meet Equation 1.
The requirement for ASTM C 186 informational testing for Type II
cement would be an additional requirement to both AASHTO M 85 and
ASTM C 150. Originally the frequency of ASTM C 186 testing was proposed
as quarterly. Subsequently the required testing frequency was changed
to at least once every six months.
These proposals passed AASHTO Subcommittee on Materials Ballots
and ASTM C01 Committee on Cement in 2006. An additional modification
was balloted to exempt Type II cements having a heat index of less
than 90 from the maximum Blaine and Wagner fineness requirement.
The use of up to 5% limestone in portland cement has been permitted
by standards in Canada and many European countries for over two
decades. Extensive
data and experience indicate that, when optimized by the manufacturer,
portland cements containing up to 5% limestone provide comparable
performance to cements without limestone. Moreover, the use of up
to 5% limestone results in significant environmental benefits.
A proposal to modify ASTM C 150 had been submitted to ASTM Committee
C01 in December of 2002 and was adopted in 2004. In January of 2006,
having reviewed the extensive data submitted during the ASTM balloting
process, evaluated additional available information on performance
of cement containing limestone since acceptance by ASTM C 150, and
considered the needs of all parties involved, the Joint Harmonization
Task Group developed a refined proposal for use of limestone in
AASHTO M 85 and ASTM C 150. The proposal included changes to permit
the use of up to 5% limestone in portland cement, clarifications
to Section 5 (renamed Ingredients), and revision of the definition
of portland cement in Section 3 of AASHTO M 85. Parallel reorganization
of Section 5 of ASTM C 150, and in the definition of portland cement
in the ASTM terminology standard, ASTM C 219. No changes would be
made to the existing chemical or physical requirements of AASHTO
M 85 or ASTM C 150.
This harmonization proposal passed ASTM Committee C01 ballot in
2006 and AASHTO Subcommittee on Materials Ballot in January 2007.
Efforts are underway to coordinate the timing of the release of
the revised 2007 editions of AASHTO M 85 and ASTM C 150, which will
have consistent provisions for fineness, Type II C3S and heat of
hydration – related criteria, and use of up to 5% limestone
in portland cement. It is anticipated that the revised standards
will be available in July of 2007.
Future AASHTO-ASTM Harmonization Activities
The work of the Joint AASHTO-ASTM Harmonization Task Group continues.
In addition to addressing remaining differences of provisions for
processing additions and Type II SiO2 limits, the task group is
considering several issues highlighted by ballot responses and task
group discussion. These include: clarification of the term sample
as used in the fineness provisions, development of separate designations
for cements with moderate sulfate resistance and moderate heat of
hydration, and evaluation of sulfate content provisions for portland
cement.
This continuing list of new work items highlights the fact that
Joint AASHTO-ASTM Harmonization Task Group accomplishments go beyond
this successful development of recommendations for resolving specific
differences in AASHTO M 85 and ASTM C 150. This group has elevated
the level of communications among AASHTO and ASTM members, established
a culture of working together to develop provisions that meet collective
needs, and developed mechanisms for implementing improvements to
cement standards. Therefore, it has established a new paradigm that
promises to enable significant technical advances to both AASHTO
M 85 and ASTM C 150, making these standards more effective and relevant
to marketplace demands!
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