Engineering Staff Attends ASTM Meeting; Provides Key Committee Updates
Following is a summary of activity at the ASTM meeting held earlier this month in Washington, DC, on Committees C09 on Concrete and C01 on Cement attended by NRMCA staff.
C09.20 Concrete Aggregates - Revisions are in progress for ASTM C136 on sieve analysis to direct the user on how to address differences between original and final weight (after sieving) of the sample. The subcommittee is developing a process for qualifying 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. The requirements vary by weathering zone that cannot be picked out clearly from the map and by the type of concrete member that is typically not known when aggregates are purchased.
C09.24 Supplementary Cementitious Materials - ASTM C618 has been revised to change the basis for classifying fly ash to the calcium oxide (CaO) content: Class F will be those that contain <18% CaO; while those exceeding this will be Class C. The sum of Si, Al and Fe oxides for both classes will be a minimum 50%. This classification will be consistent with guidance in the practice for AAR, ASTM C1778. In ASTM C311, a variation of strength activity index that will evaluate strength contribution due to water reduction and chemical reactivity was balloted as an appendix. 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 proposed specification for ground glass pozzolan is working through the balloting process. A task group was established to develop a separate specification for natural pozzolans (these are currently covered in ASTM C618). The group will define methods that will verify the pozzolanic characteristics of these materials to distinguish them from inert fillers. One approach included raising the strength activity index limit. Under new business, a new class of pozzolan from ground bottom ash will be proposed in ASTM C618.
C09.40 Ready Mixed Concrete - Minor revisions were approved to specifications C1602 (water), C1798 (returned concrete) and C94 (ready mixed concrete). The bulk of the meeting was spent resolving 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 proposed revision will move forward to be considered by the C09 main committee. Negative voters have indicated their preference to retain the 90-minute delivery limit as a default. The proposal is for this to be established during the ordering process so that the appropriate mixture can be produced and delivered with an agreed upon delivery time. 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; revise the delivery ticket section for clarity and revise technician certification requirements by referencing C1077. In C1602, revisions will be proposed to reference a standard for potable water and to change the reference standards for measurement of sulfates and chlorides.
C09.50 Risk Management for Alkali Aggregate Reactions (AAR) - The subcommittee considered a proposal to require SCMs with a high alkali content, except for natural pozzolans, to be tested by ASTM C1293. This proposal was not successful. The subcommittee will ballot to withdraw the older mortar bar test for ASR, C227, because its results lack reliability to field performance. The subcommittee has four task groups (TG): 1. Improve the flowchart for establishing the reactivity of aggregates in C1778; 2. Finding a correlation between ASTM C1293 and ASTM C1260 with existing data with consideration of field performance; 3. Define multiple prevention levels for the performance based approach similar to the prescriptive approach; 4. Improve the process of classifying risk of ASR to different types of structures.
Additional guidance will be provided on aggregate testing frequency. ASTM C1778 will be revised to include considerations for the use of ground glass and natural pozzolans containing high alkalis, and use of blended cement and blended supplementary cementitious materials. The subcommittee will schedule presentations on the mini concrete prism test, the autoclave test for cement and testing aggregates for iron sulfides.
C09.60 Fresh Concrete Tests - A new method for measuring the electrical resistance of fresh concrete was re-balloted and received several comments that must be resolved before it is finalized. The subcommittee will initiate a ballot on a new standard for the K-slump tester that measures workability. The prevision version of this test method, C1362, will be removed. Revisions to C1064 on temperature and the pressure method have been proposed. It will clarify that the verification of accuracy of the meter is pertinent to the base and top and these cannot be switched. The subcommittee received a presentation on a prototype device that is being developed to measure the air void system in fresh concrete using an acoustic air void spectrometer (by Dynaflow). The device measures air void distribution using different sound wave frequencies that excite different bubble sizes. Sound speed and attenuation of acoustic waves are affected by bubble volume and size.
C09.61 Strength - A revision was approved to C31 to better outline the requirements for initial curing of strength test specimens in the field. There are no significant technical changes in this revision but an improvement on the clarity of the requirements. There are several minor revisions in progress for the standards on testing cores, C42, testing compressive strength, C39, and the practice for making and testing concrete in the laboratory, C192. A new standard was balloted on evaluating the long-term strength of concrete containing calcium aluminate cement. The subcommittee discussed additional requirements for reporting strength test results, establishing test age tolerances for testing beams, C78, and 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 - The subcommittee attempted to remove the test method measuring the permeable voids in concrete test, ASTM C642, because of its poor precision but could not because it is still used. They discussed improving the method, including the use of vacuum. For a similar reason, the deletion of the chloride ponding test, ASTM C1543, used to evaluate durability of concrete has been withdrawn. The method is an AASHTO standard. The subcommittee reviewed ballot results on a proposed bulk resistivity test and will revise the standard to respond to the comments. Work continues on standardizing the surface resistivity test method. Degree of saturation of the specimens and pre-conditioning specimens prior to measuring resistivity is a significant factor impacting the results. Resistivity of concrete is evolving as the preferred method of evaluating the durability of concrete. The subcommittee is working on the development of a new guide to calculate the formation factor of concrete which provides a property characterizing permeability of concrete. The results of the electrical tests are used to determine the formation factor.
ASTM C09.67 Resistance to Environment - Various revisions to the test method to evaluate the freeze-thaw durability of concrete, ASTM C666, will be balloted. One of the proposed revisions was to add an appendix to suggest including 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.
C09.98 Evaluation of Laboratories - A revision is in progress to ASTM C1077 to clarify criteria for certification programs for technicians. A proposal was balloted to permit licensed professionals other than professional engineers, such as architects, to serve as technical directors of testing agencies. This proposal was not supported and alternatives are being considered.
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 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 include a requirement to report the chloride content and to evaluate the potential for early stiffening of blended cements (in C595). It was reported that AASHTO has established a program to test cements under its NTPEP program. Cement samples will be evaluated every quarter by independent labs for conformance to the cement specifications. Some states require participation in NTPEP to qualify materials for transportation construction; some will not do their own internal testing to approve sources. Research continues to evaluate the reliability of the autoclave expansion test that is intended to evaluate the soundness of cement (potential to cause expansive cracking when used in concrete). This research will develop information to revise cement standards if necessary.