NRMCA Staff Files Summary of ASTM Meeting on Concrete, Cement

The following is a summary of activity at the ASTM meeting held earlier this month in Houston of Committees C09 on Concrete and C01 on Cement attended by NRMCA staff:

C09.20 Concrete Aggregates - Minor revisions were approved to ASTM C136 (sieve analysis), C70 (aggregate moisture), C566 (total moisture content of aggregates), C40 (organic impurities), C123 (lightweight particles in aggregate) and C131 (abrasion resistance). A proposal is being developed to remove the weathering map in ASTM C33 (specification for aggregates) that will impact requirements for coarse aggregates. Data was presented on evaluating carbonate based mineral fillers (ASTM C1797) for sulfate resistance with an intent to include testing requirements in the specification. Minor revisions were approved to ASTM C638 and C637 – standards for heavyweight aggregates for concrete for radiation shielding.

C09.24 Supplementary Cementitious Materials - A new specification for ground glass pozzolan was approved. Glass from glass containers, windows and auto windshields and from glass fiber reinforcement, crushed to fine particle size can be used as a pozzolanic ingredient in concrete. There are different classifications of ground glass depending on source. For testing pozzolans, a variation of strength activity index (SAI) that will evaluate strength contribution due to water reduction and chemical reactivity is being evaluated and could become a test method. Other measures of pozzolanic activity continue to be researched; these include measures of chemically-bound water; heat of hydration based on calorimetry; calcium hydroxide consumption and a lime-based strength reactivity index test. The first two measures have been balloted.

A proposal to include crushed bottom ash (from coal burning) is proposed as an addition to the specification for fly ash and natural pozzolans, ASTM C618. A note in C618 will clarify that high loss on ignition of natural pozzolan is not associated with carbon that causes air entrainment problems as it does for some fly ash. It is also recognized that some natural pozzolans have a higher water requirement and could be approved for use provided performance is not impaired. Other revisions in progress at the subcommittee level include: use of fly ash that could include blended fly ash or blends of fly ash with harvested fly ash; developing a performance-based specification for SCM for use in concrete and specification for colloidal silica as a SCM for use in concrete. A draft specification for natural pozzolan is being developed with the possibility that this will be separated from ASTM C618 which will be limited to coal-combustion byproducts. ASTM C618 could include crushed bottom ash and harvested ash. With these developments, it is recognized that there is an increased need for SCMs for use in concrete while the specifications should ensure that they prevent inert materials that do not provide cementitious benefits from being qualified.

C09.40 Ready Mixed Concrete - The subcommittee addressed negatives on the proposal to replace the 90-minute time limit for delivery to be replaced by limit set by the producer or purchaser that would be applicable to project conditions or the type of mixture. The passage of this proposal was not successful in deliberations at the main committee. A revision to C94 was approved to clarify qualifications of laboratory technicians. Other work in progress is to require a retest when tests fail slump and air content to include a reference to the specification for mineral fillers, C1797 and blended SCMs, C1697, in C94; address scheduling and performance-based orders in the ordering section and to including a requirement to state the allowable water that can be added at the jobsite on the delivery ticket.

C09.50 Risk Management for Alkali Aggregate Reactions (AAR) - Several proposals are in progress: evaluating efficacy of SCMs with a high alkali content with a 2-year concrete prism test (C1293). This would not apply to natural pozzolans; rather to clarify the flowchart in ASTM C1778 (practice for AAR) and to better define the conditioning period before measurements are made on specimens in C1293. Guidance on interpretation of results in the appendices of ASTM C1567, C1260 and C1293 will be removed to be replaced with reference to C1778.

The subcommittee was offered a presentation to evaluate leaching of alkalis in the C1293 concrete prism test. Promising approaches included using cylinders instead of prisms; using of larger specimens and using an inverted plastic bag over the top 2/3rd of the specimen. Reducing leaching could change to scope of the test method by removing the requirement to add additional alkalis to the mixture to potentially evaluate cement at different alkali contents.

C09.60 Fresh Concrete Tests - A new standard for using K-slump tester to measure workability was approved (this was previously ASTM C1362). A proposed revision to consolidating concrete in the slump cone received several negatives and was withdrawn. A new method for measuring the electrical resistance of fresh concrete is still in the works. The subcommittee received a presentation of a prototype device that is inserted in fresh concrete to measure air content and specific surface (as a measure of the air void system). The device is referred to as the shock wave air meter (SWAM) and has shown reasonable correlation to air void system in hardened concrete in evaluations at Georgia Tech.

C09.61 Strength - Revisions are being considered to include the sample ID and delivery ticket number on the report for making cylinders, ASTM C31, and the strength test report, C39. Minor revisions were approved to ASTM C31 (making and curing test specimens and C39 (testing strength), and C192. Revisions to C31 on improved language for initial curing in the field are in the works. The subcommittee is finalizing a precision statement for ASTM C469 - measuring the modulus of elasticity of concrete based on results of a recently completed inter-laboratory study (ILS).

C09.66 Fluid Penetration - The subcommittee will ballot to withdraw ASTM C1760 (bulk conductivity) and ASTM C642 (hardened concrete voids by boiling) test methods. The newer standard C1876 (bulk resistivity) is a replacement that provides similar information to C1760. ASTM C642 is being withdrawn because of the uncertainty of the property it measures and its high variability. Some changes are being developed to C1876:

1. A procedure to standardize the readings of the equipment before the test;

2. Clarify that specimens are to be immersed in lime-saturated simulated pore solution when demolded at 1 day;

3. Include an option for accelerated curing of test specimens (similar to ASTM C1202); and

4. Establish a time limit for taking resistivity readings after specimens are removed from the solution.

Conditioning test specimens in lime water will be considered when more data is available. A revision to ASTM C1202 (rapid chloride permeability) to address a correction to the result for the specimen thickness was discussed. The subcommittee is planning interlaboratory studies to develop precision estimates for ASTM C1876, C1202 and C1556 (diffusion coefficient). NRMCA is involved in these efforts and will be a participating laboratory. The subcommittee received a presentation regarding simplifying specimen conditioning in ASTM C1585 (sorptivity of concrete). These changes could improve the correlation between initial sorptivity and other parameters such as resistivity and w/cm.

ASTM C09.67 Resistance to Environment - The subcommittee is planning an interlaboratory study to develop a precision statement for ASTM C666 – testing the freezing and thawing resistance of concrete.

C01.10 Hydraulic Cement - Revisions to cement standards are coordinated to ensure consistency between ASTM and AASHTO specifications for hydraulic cement. With the removal of a low alkali option in ASTM C150 for portland cement, efforts are ongoing to educate specifiers on this change. As part of this effort, a database of state highway agency specifications related to requirements for cement and alkali aggregate reactions has been developed. A revision was approved to ASTM C595 (blended cement) to report the chloride content, if requested. A revision to ASTM C1157 (performance spec for cement) to revise the heat of hydration limits to be based on isothermal calorimetry – these changes were previously approved to the other cement specifications.

For more information, contact Colin Lobo at clobo@nrmca.org.