NRMCA Attends Recent ASTM Committee Meetings in Denver
Earlier this month, NRMCA Engineering Staff traveled to Denver to attend the American Society of Testing Materials meeting of Committees C09 on Concrete and C01 on Cement. What follows are summaries of activity of those committees:
C09.20 Concrete Aggregates - ASTM C136 on sieve analysis is being revised to address excessive differences between original and final weight (after sieving) of the sample. The subcommittee reviewed a proposal to qualify carbonate-based mineral fillers for use in concrete exposed to sulfates in specification C1797. The subcommittee is considering the deletion of the weathering zone U.S. map and simplifying the physical requirements for coarse aggregate in Table 4 of Specification C33. Revisions are in progress to C566 (total moisture content of aggregates), C40 (organic impurities), C123 (lightweight particles in aggregate) and C131 (abrasion resistance).
C09.24 Supplementary Cementitious Materials - In ASTM C311, a variation of strength activity index (SAI) that will evaluate strength contribution due to water reduction and chemical reactivity was balloted as an appendix. The subcommittee is considering developing this as an independent test method. The subcommittee is evaluating other measures of pozzolanic activity to include measures of chemically bound water; calcium hydroxide consumption; heat of hydration based on calorimetry and a lime-based strength reactivity index test. The first two approaches are being developed as test methods. A presentation on the lime-based test showed promise as inert fillers did not gain strength. A proposed specification for ground glass pozzolan is working through the balloting process.
A ballot to raise the strength activity index limit of natural pozzolans from 75 to 80 to eliminate some inert fillers was not successful. As an alternative, a note will be considered to clarify that meeting the SAI limit does not guarantee concrete performance such as improved durability. Also, a note will be added to permit water requirement that exceeds 115% for natural pozzolans provided concrete performance was acceptable. A ballot to add a new class of pozzolan in ASTM C618 for ground bottom ash (GBA) was not successful. Revisions to include GBA and harvested ash (extracted from landfills) was discussed. A specification for colloidal silica will be balloted. Under new business, a new performance specification for SCMs was discussed; Also, a revision is being proposed to ASTM C618 for blending materials, including processing additions, to produce fly ash that conforms to the specification.
C09.40 Ready Mixed Concrete - The bulk of the meeting was spent resolving negatives from the main committee 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. Revisions will be made based on some comments and the proposal will be balloted again. 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 revise technician certification requirements by referencing C1077.
C09.50 Risk Management for Alkali Aggregate Reactions (AAR) - The subcommittee is balloting several proposals: to require SCMs with a high alkali content, except for natural pozzolans, to be tested by ASTM C1293; to clarify the flowchart in ASTM C1778. The older mortar bar test for ASR, C227, was withdrawn because its results lack reliability to field performance. Presentations on possible new ASR tests - the mini concrete prism test, the autoclave test, and the concrete cylinder test - were made at the meeting. Subcommittee formed an informal task group to monitor the progress of the pyrrhotite issue and the need for tests. There was discussion regarding the reliability of results ASTM C1293 as it relates to field performance because test concrete blocks made with similar mixtures were failing after 10-15 years. However, no failure related to ASR has been reported in field applications which incorporated ASR mitigation measures such as the use of fly ash.
C09.60 Fresh Concrete Tests - The subcommittee considered a new standard for the K-slump tester that measures workability (this was previously ASTM C1362). A new method for measuring the electrical resistance of fresh concrete is still in the works. A revision to the consolidation in the slump test was approved to address consolidation problems with lower slump concrete. Rodding will be from the outside moving inward for the bottom layer.
C09.61 Strength - Revisions are being considered to include the delivery ticket number on the report for making cylinders, ASTM C31, and the strength test report, C39. Some indicated that this information was not always provided to the laboratory performing the strength tests. Other minor revisions are being considered to ASTM C31, C39 and C192. The subcommittee considered a suggestion that air content should not be measured for non air-entrained concrete when strength specimens are made, but the suggestion was not supported. The subcommittee is finalizing a precision statement for measuring the modulus of elasticity and Poisson’s ratio by ASTM C469, based on results of a recently completed inter-laboratory study (ILS).
C09.66 Fluid Penetration - A new test method for measuring the bulk resistivity of hardened concrete was approved. The method would be an alternative method of providing an indication of the permeability of concrete. Other issues will be considered for future revisions, including the need for a verification cylinder, accelerated moist curing and establishing a time limit for taking resistivity readings after specimens are removed from the solution. A revision to ASTM C1202 (rapid chloride permeability) will address a correction to the result for the specimen thickness. The subcommittee is planning interlaboratory studies on several methods under its purview to obtain improved precision statements. Methods include the bulk resistivity method and ASTM C1556, chloride diffusion coefficient.
ASTM C09.67 Resistance to Environment - A revision is in the works to ASTM C666 (freeze thaw resistance) to clarify the duration of the freezing and thawing cycles. A suggestion was considered for an appendix that would address a petrographic evaluation of tested specimens to evaluate whether deterioration to specimens is caused by non-durable aggregate as opposed to the lack of a good air void system. This was not supported.
C01.10 Hydraulic Cement - Revisions to cement standards are coordinated to ensure consistency between ASTM and AASHTO specifications for hydraulic cement. Recent revisions to ASTM C150-19a include removal of the low alkali option (0.60% Na2O eq.) for portland cement with a requirement to report the alkali content for all cement types; revise the heat of hydration limits for Type II (MH) portland cements; and deletion of the Wagner method of measuring the fineness. Revisions to the specification for blended cement, C595, include removal of the Option R for alkali silica reactivity mitigation of cement; remove the evaluation of the alkali reactivity of pozzolan used in blended cement; and to define the heat of hydration limits based on C1702 (isothermal calorimetry). Revisions being considered is a requirement to report the chloride content and to evaluate the potential for early stiffening of blended cements (in C595).