Astm Committees Weigh Scc, Scm, Wash Water, Specimens

National Ready Mixed Concrete Association’s Colin Lobo, vice president of engineering, and Karthik Obla, senior director of research and materials engineering,

National Ready Mixed Concrete Association’s Colin Lobo, vice president of engineering, and Karthik Obla, senior director of research and materials engineering, track ASTM International Concrete and Cement committee activity on behalf of the industry. In a recent update, they cite key developments affecting ready mixed production or cast-in-place concrete standards:

  • A third standard on self consolidating concrete has been approved, specifically to measure segregation potential. The subcommittee will not attempt to standardize the L Box or U Box test at this time. A standard to describe a new simple static segregation test presented by University of Illinois will be developed.
  • A revision to ASTM C 31 will recognize 4- _ 8-in. specimens as standard size along with 6- _ 12-in. specimens. This action is consistent with an approved change in ACI 318 (to be released in 2008) that will permit either size for strength tests.
  • The subcommittee responsible for ASTM C 94 has proposed a significant revision of the ordering section for ready mixed concrete by prescription or performance. Several negative votes have been addressed at the subcommittee level with the item moving forward to broader balloting. The subcommittee is also developing wording for reuse of returned concrete (termed top-loaded concrete) that will be issued for letter ballot. A ballot will attempt to eliminate the optional chloride limit for wash water, as the ACI 318 limit for concrete is more appropriate.
  • The subcommittee on Supplementary Cementitious Materials (SCM) is developing a provision that will allow the use of blended fly ashes and slags.
  • An approved revision to ASTM C 595 on blended cements will simplify the nomenclature for these cements to IP with pozzolans and IS for slag. Further, the quantity of supplementary cementitious material will be stated in the cement designation; for example, a IP (20) will contain 20 percent fly ash (or pozzolan) by mass.
  • The subcommittee on chemical admixtures is proposing a new class of admixtures in C 494 that will qualify special performance materials by demonstrating no negative performance effects on concrete. This classification can be used to qualify admixtures until pertinent specification requirements for the special performance can be developed. The subcommittee is also formulating a standard to measure setting time using thermal methods.
  • The subcommittee on Slag is proposing to permit the use of interground sulfate with high alumina slags in C 989 for improved performance.
  • A new subcommittee on Cementitious Admixture Interactions has developed a procedure to evaluate the compatibility of cementitious materials and admixtures based on relative heat curves Û a procedure balloted during the last cycle. Discussions illustrated that results on pastes tended to magnify the effect of cement admixture interactions not generally seen in mortars and concrete.

Developing tests for pervious concrete

Reflecting the significant interest in pervious concrete within the building and paving community and the need for standardized tests to invoke in project specifications, ASTM Committee C09 Û Concrete and Aggregates plans to begin developing standards for pervious concrete at its December meeting in Atlanta. The formational meeting, tentatively scheduled for Monday, Dec. 4, will establish the scope and potential test methods to be developed by a subcommittee under C09. NRMCA’s Karthik Obla, senior director of research and materials engineering, is chairing subcommittee, pending a nod from the C09 executive subcommittee. Û 240/485-1163; [email protected]