Q. How long must concrete be protected from freezing temperatures, with and without accelerators or admixtures?
ASTM’s ready-mixed concrete specification says, “air content of air-entrained concrete when sampled from the transportation unit at the point of discharge” is to be within 1.5% of the specified value. What does the “transportation unit” mean? Is ASTM referring to the mixer truck, end of pump line, conveyor, etc. as the transportation unit?
A. You’ve highlighted one of the more important details to understand about ASTM C94, “Standard Specification for Ready-Mixed Concrete.” Philosophically, the key is to distinguish between transportation and placement. In practice, that means the concrete is sampled as it is discharged at the jobsite, which includes from trucks or directly from the mixer.
For details of the sampling procedure, this document refers to ASTM C172, “Practice for Sampling Freshly Mixed Concrete.” C172 is more specific, saying that it pertains to sampling “from stationary, paving and truck mixers, and from agitating and non-agitating equipment used to transport central-mixed concrete." The transportation units referred to in C94 would be taken from that list.
This document also gives specific directions on how to obtain samples from these sources. For example, you sample a drum truck mixer by “repeatedly passing a receptacle through the entire discharge stream or by completely diverting the discharge into a sample container.” It doesn’t mention sampling the discharge from pumps, conveyors, and wheelbarrows that are used to place the concrete after it has been delivered.
The second important thing to note about C94 is this: “In any case where the requirements of the purchaser differ from these in this specification, the purchaser’s specification shall govern.” In other words, the purchaser may have additional requirements for accepting concrete at the point of placement. However, these must be clearly incorporated into the project specifications because they are not covered by C94.
Keeping up with the Specs
Producers should be aware that the ASTM scientific committee is trying to transform sustainability topics from marketing efforts into measurable performance standards. For five years, members of ASTM subcommittee E06.71 on Sustainability, part of Committee E06 on Performance of Buildings, have been working hard to develop a scientific response to the technical issues.
In the April 2004 ASTM Standardization News, Dru Meadows, chairman of E06.71, summarized current committee activities. In ASTM E2114, Sustainability Relative to the Performance of Buildings, sustainability is defined as ”the maintenance of ecosystem components and functions for future generations.”
The standard also defines sustainable development as “the development that meets the needs of the present without compromising the ability of future generations to meet their own needs.” With this in mind, the committee has been working to address sustainability’s three primary considerations—environmental, economic, and social.
Meadows’ subcommittee is coordinating with other ASTM committees. A major effort is compiling the ASTM International Standards on Sustainability in Buildings. This wide-ranging document has 127 standards that address everything from performance of wetlands to building design.
There are several efforts close to final comment periods. These include:
Environmentally Preferable Products: The federal government and several states have drafted initiatives to encourage purchasing environmentally preferable products. E06.71 has been developing standards to help establish a consistent approach to evaluate and document these products. Their current work includes evaluating life cycles as referenced in E219, Data Collection in Sustainable Assessment of Building Products.
Building sustainability: The subcommittee is developing a draft that may become a “Guide for General Principles of Sustainability Relative to Buildings.” The standard will identify issues associated with the decision-making process used to balance environmental, economic, and social issues.
Building elements and sitework: The subcommittee is also developing a draft standard that deals with the construction, renovation, retrofit, and reuse of the building. The “Classification for Sustainable Building Elements and Related Sitework” will focus on the major building components, rather than the building’s operation.
Green Roofs: A green roof is an assembly that supports a planting or landscaping area on a man-made structure. A vegetation zone on top of buildings or other structures can reduce stormwater runoff and provide a growing medium for plants that can help reduce heat island temperature gains. Meadows’ subcommittee is considering several standards that address performance metrics for green roofs.
Earthen Building Systems: The subcommittee is developing standards to define performance aspects of adobe, rammed earth and straw, and other building systems.