When Will U.S. Standards For Air Entrained Concrete Modernize?

I have just completed an exhaustive review of both contemporary and past U.S. Standards related to required/recommended air contents for concrete, and it saddens me to report that my findings were grim.

My research included ACI and ASTM Standards going back over 50 years, and in this respect, U.S. Standards are not keeping pace with modern technology.

It is time for change.

Today we live in an age where newer generation synthetic resins capable of producing air-void systems consisting of much smaller and more closely spaced bubbles compared to traditionally used wood-derived acid salts, mainly neutralized vinsol resin, are in common use. These newer generation AEA’s have been in use throughout the concrete industry for more than 20 years.

My recent exercise consisted of comparing the air content tables contained in contemporary and past versions of ACI 201, ACI 211, ACI 318 and ASTM C94. The earliest version of ASTM C94 that I have in my library referencing a table for “Total Air Content for Air-Entrained Concrete Exposed to Cycles of Freezing and Thawing” is ASTM C94-65. In 1933, the provisional version of ASTM C94 contained no reference to recommended air contents simply because air entrained concrete did not yet exist, or at least was about 20 years from becoming mainstream to the industry. The air content tables contained in these industry standards were and still are based on air entrained concrete produced with neutralized vinsol resin.

It has been demonstrated numerous times using both "labcrete" and "realcrete" that typically, a two percent reduction in total air content when using a synthetic "micro" AEA would result in equivalent or superior freeze-thaw durability compared to concretes having a higher total air content produced with a traditional neutralized vinsol resin. Conversely, attempting to produce air contents higher than necessary for freeze-thaw resistance with synthetic AEA’s run a greater chance that the measured compressive strength will be lower and even below acceptance limits.

In many cases, the low strengths that have resulted from the inappropriate use of modern synthetic AEA’s have resulted in: (1) delays to project schedules, (2) disputes, (3) litigation, and in some cases, (4) complete removal and replacement of the concrete in question.

All it would take to preclude future and such unnecessary problems and further the U.S. concrete industry’s advancement into the 21st century would be to add a footnote to existing air content tables. Here is one suggestion:

“When an air entraining admixture capable of producing air-void systems consisting of small, closely spaced air voids is used, a reduction of XX percent to the above stated values is permissible. It must be demonstrated through qualification testing for the class of concrete used in the work that the air entraining admixture is capable of producing an equivalent or higher durability factor.”

Based on personal experience using synthetic AEA’s, a 1.5 or 2.0 percent reduction is recommended. Obviously, the concrete should be “realcrete” as opposed to “labcrete.” A representative batch can be produced at a concrete production facility and delivered to the laboratory for specimen fabrication and testing. For evaluation, ASTM C666 (Procedure A) is recommended.

If anyone is aware of committees within ACI or ASTM working individually or jointly with respect to this matter, please let me know. I am aware of none.

Changes of this nature take time. If begun tomorrow, we should see changes hopefully within the next five to ten years.