Q. As a producer, how can I use the recent changes in ASTM standards to use process water in my concrete?
A. We turned to three experts to answer this important question. The answer below is supplied by Richard S. Szecsy, PhD, PE, vice president, new product development and risk management, Lattimore Materials Co., McKinney, Texas; Colin Lobo, PhD, PE, vice president, engineering, NRMCA; and Steve Parker, vice president, aggregate development, RMC Mid-Atlantic and chairman, ASTM Sub-Committee 09.40 for Ready-Mixed Concrete.
While changes in concrete and construction sometimes come at a glacial pace. But such changes also tend to be significant. One such change occurred at the semi-annual ASTM meeting in June. After eight years of development, and more than 20 years of existing as a part of another standard specification, a new document was created: ASTM C 1602/C1602M-04, “Standard Specification for Mixing Water Used in the Production of Hydraulic Cement Concrete.”
Every other product used in producing ready-mixed concrete has its own Standard Specification within ASTM. Water has traditionally been specified within ASTM C 94 Standard Specification for Ready-Mixed Concrete.
Reusing recycled water was recognized back in the early 1970s and ASTM C 94 accommodated that need by allowing its use in 1978. The provisions remained unchanged since then.
The resulting provisions within ASTM C 94 were ambiguous and confusing. The testing requirements and qualifications for the water were not practical and not based on the final performance of the concrete. As such, they were not generally accepted, and very rarely put into practice.
On the operational side, the requirement of complying with environmental regulations has increased ten-fold, with recent enforcement construing violations of the Clean Water Act as criminal violations. The volume of recycled water produced at a concrete production facility is significantly higher than that which can be reused and/or processed for discharge economically.
State highway agencies have not picked up on allowing the use of wash water while state environmental regulations have gotten more severe. Only about ten state agencies address the using wash water in their specifications, and all these provisions are more restrictive than ASTM C 94. This is an inherent conflict as state highway specification requirements are trickled down to commercial construction.
In the meantime, the ready-mixed concrete industry has incorporated a high level of innovation on the operations and technology side to consume a larger volume of recycled water in ready mixed concrete while maintaining the quality of the delivered product to attempt to be environmentally responsible and comply with regulations. In some cases, this has not been without liability on the part of the producer, not necessarily for failing a specification requirement, but for non-conformance as perceived by the specifying authority.
The statistics can be astounding. Using conservative estimates, the volume of returned concrete exceeds 15 million cubic yards and the volume of process water generated exceeds 8 billion gallons annually. This does not include stormwater quantities that also need processing at production facilities. The annual cost to the industry for environmental management practices is estimated at $60 million.
Change at last
Knowing that a change was needed, the stage was set, but the first ASTM ballot attempt to update the water requirements of C 94 was defeated in 1998. This was repeated for the next several years no matter how the proposed changes were presented or modified.
The task group responsible for water decided the issue had become too large and complex to simply leave within the C94 document. A decision was made to draft a new ASTM specification specifically for water to be used in concrete (ASTM C 1602-04). This move would also require a new ASTM test method to determine the solids content in water (ASTM C 1603-04). These documents were defeated in 2003. These documents were then refined and again passed with little resistance in June 2004
What do they mean to the industry? The ability of the concrete producer to better manage and utilize all of his potential water sources, without compromising the durability aspects of the concrete, is perhaps the single largest impact. The environmental and attendant prosecutorial challenges are also more easily dealt with while honoring the requirements of C94. However, not to be overlooked is the fact that the new specification (ASTM C1602) regarding using water is now much more performance-based compared to the highly prescriptive elements previously found in C 94.
While the essential requirements didn’t change, the specification defines a practical and performance-based process evaluating water for qualifying its use. The general problems with using washwater are understood and the solutions to these problems are available.
ASTM C 1602 allows progressive producers who want to tackle their mass balance situation (volume generated versus volume consumed or discharged) to do so, while at the same time protecting the purchaser. This gives the concrete producer an opportunity to best utilize his expertise and knowledge of concrete and concrete-making materials.
With change comes opportunity; further changes toward a performance-based environment will bring new opportunities for enhanced concrete performance while offering cost savings to both the producer and purchaser.