NRMCA Engineering Staff attended the ASTM meeting in Chicago held earlier this month of Committees C09 on Concrete and C01 on Cement. Following is the report of key developments:

C09.20 Concrete Aggregates - A new specification for mineral fillers for use in concrete was approved. The specification was developed to permit the use of finely ground materials originating from aggregates to be used in applications such as self-consolidating concrete and other uses. Mineral fillers include finely ground calcium carbonate or other crushed fines from aggregate, referred to as Aggregate Mineral Filler (AMF). Three types of mineral filler are recognized with differences in the minimum requirements to qualify for use. The subcommittee is developing a revision to delete the appendix to C33 that provides guidance on alkali aggregate reaction and refer to practice ASTM C1778 on alkali aggregate reactions. Revisions are in progress for ASTM C29 on bulk density of aggregates, splitting samples and some other quality tests.

C09.24 Supplementary Cementitious Materials - The subcommittee has drafted a new specification on colloidal silica. These are nano-sized silica particles in a liquid suspension. Specifications are being drafted for natural pozzolans and ground glass for use as supplementary cementitious materials. The specification for fly ash, C618, is considering a clause that recognizes the use of ponded ash. A proposal will revise the strength activity index using volume replacements of fly ash as opposed to weight. Changing the classification criteria for fly ash on the basis of calcium oxide content is also being considered, as this will line up better with alkali silica standards. The mission of the subcommittee is being revised to allow it to develop standards for other types of supplementary cementitious materials. A revision will remove testing provisions for alkali silica reactions in the fly ash specification and include an appendix that refers to C1778.

C09.26 Chemical Reactions - A ballot will be developed to remove guidance in the appendices of the ASR test methods and refer to ASTM C1778. A ballot will propose removing the older mortar bar test, C227, as it does not provide reliable results. Subcommittee will consider developing guidance for testing mineral fillers for potential for alkali silica reactivity.

C09.40 Ready Mixed Concrete - The new specification on reusing returned concrete is now available – ASTM C1798-16. There were no revisions approved to C94; the current version is dated 2016. Several revisions are working through the process:

• A reference in C94 to the new specification C1798 that would permit the use of returned concrete with the approval of the purchaser;

• Eliminating time limits to delivery (90 minute);

• Addressing the use of admixtures at the job site for mixture adjustments;

• Clarifying language for batching tolerances for aggregates;

• Requiring a retest on a separate sample when failing slump and air content;

• Enhancing the Annex and associated clauses related to mixing uniformity evaluation;

• Defining mixing water and batch water;

• Revising notes related to process of low strength evaluation;

• Revising section related to technician certification – to refer to ASTM C1077; and

• Indicating that job site water adjustment should be permitted when a max slump is specified.

C09.50 Risk Management for Alkali Aggregate Reactions (AAR) - The subcommittee is working with initiatives to remove recommendations on AAR in various standards and to refer to ASTM C1778. The Cement and Concrete Reference Laboratory (CCRL) has started a proficiency sample program for ASTM C1260 – the accelerated mortar bar test. The subcommittee is collecting data that compares ASTM C1260 and C1293 data for alkali silica reactivity. Aggregate mineralogy might impact the results in these different methods. 

C09.60 Fresh Concrete Tests - Revisions are in process for the method to measure density or unit weight of fresh concrete (C138). Included is a sample calculation on yield, gravimetric air content and other factors that can be determined in this method. A precision statement based on a recently completed interlaboratory study is being proposed for the pressure air method (C231).

 

A new practice on measurement of electrical resistivity of fresh concrete was balloted; a revised version will be proposed based on comments from previous ballots.

C09.61 Strength - A proposed revision was to require the method of curing and the max-min temperatures during initial curing in the field on the ASTM C39 strength test report (this info is in the reporting section of ASTM C31). The proposed revision did not pass. The subcommittee approved a revision to C39 that defines the specimen age from the time it is cast and revisions have been proposed to define time tolerances to different test ages for strength measurements. Several other revisions are in the works for the standards on strength.

C01.10 Hydraulic cement  - Revision to cement standards are coordinated with the ASTM AASHTO harmonization task group to ensure the requirements in the equivalent ASTM and AASHTO specifications are consistent.

 

For ASTM C150, a revised note was approved that clarifies limestone additions. A revision on reporting total chlorides is being finalized. For ASTM C595, revisions approved include a removal on a restriction to use portland-limestone cements (Type IL) for sulfate resistance when appropriately qualified by test; revision of the minimum strength levels that are similar to those in C150 and adding reporting requirements for blended cements that are needed for developing mixtures for alkali silica reactivity (ASR) in accordance with ASTM C1778. The subcommittee will propose removing the optional limit that characterizes a low-alkali cement as the alkali loading of concrete is more relevant to ASR. Heat of hydration limits based on isothermal calorimetry will be incorporated in the cement standards to supplement and eventually replace limits based on the heat of solution method, C186.