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 8 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/C 1602M-04, “Standard Specification for Mixing Water Used in the Production of Hydraulic Cement Concrete.”
Every other product used to produce ready-mixed concrete—cements, admixtures, supplementary pozzolanic materials, fibers—has its own Standard Specification within ASTM. But water has traditionally been specified within ASTM C 94, “Standard Specification for Ready-Mixed Concrete.”
The desirability of reusing recycled water was recognized in the early 1970s, and ASTM C 94 allowed its use in 1978. The provisions addressing the composition and quality of water have remained unchanged since then.
The provisions in ASTM C 94 for mixing water—especially recycled water—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 rarely practiced.
On the operational side, new environmental regulations have increased ten-fold, with recent violations of the Clean Water Act being treated as criminal acts. The volume of recycled water produced at a concrete production facility is significantly higher than what can be reused or processed for discharge economically.
Drive-over collection systems such as this already make it easy to collect washout water from ready-mix trucks. New water-related standards should help designers, contractors and concrete producers agree on what water can be reused.
State highway agencies have not allowed the use of wash water as concrete mixing water, while at the same time state environmental regulations have gotten more severe for discharged water. Only about 10 state DOTs address using wash water as mixing 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 trickle down to commercial construction.
In an attempt to be environmentally responsible and compliant, the ready-mixed concrete industry has found ways to consume more recycled water in ready-mixed concrete while maintaining the quality of the delivered product. Sometimes, though, the producer has been found liable, not necessarily for failing a specification requirement, but for non-conformance as perceived by the specifying authority.
The statistics are astounding. Conservatively, 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 that falls on the grounds of a ready-mix plant that also needs to be treated prior to discharge. The annual cost to the industry for environmental management is estimated at $60 million.
Change at last
Knowing that a change was needed, the stage was set, but the first 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 water task group decided the issue had become too large and complex to simply leave it within C 94. The committee decided to draft a new ASTM specification specifically for water to be used in concrete (ASTM C 1602-04). This move required creation of a new ASTM test method to determine the solids content in water (ASTM C 1603-04). These documents were written and proposed, but were defeated in 2003. After some refinement, however, they passed with little resistance in June 2004.
Now the change is complete and the new documents are available to use—but what does this mean for the industry? Perhaps the greatest impact is that the new specification and test method allow concrete producers to better manage and use all of their potential water sources, without compromising the concrete's durability.
Based on performance
The new standards also make environmental challenges easier to deal with while still honoring C 94's requirements. The new specification is much more performance-based when compared with 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 for evaluating water that can be used for mixing and for qualifying that water's use. The problems associated with using wash water are understood, and solutions are available.
ASTM C 1602 allows progressive producers who want to tackle their mass balance situation (volume of water generated versus volume consumed or discharged) to do so, while at the same time protecting the purchaser of the concrete. This gives producers an opportunity to use their expertise and knowledge of concrete and concrete-making materials to everyone's advantage.
We anticipate that further changes toward a performance-based environment will bring new opportunities for enhanced concrete performance while offering cost savings to the producer and the purchaser.
For more information, contact Richard Szecsy at 972-221-4646, or e-mail email@example.com.
— Richard S. Szecsy, PhD, P.E., is vice president, new product development and risk management, Lattimore Materials Co., McKinney, Texas. Colin Lobo, PhD, P.E., is vice president, engineering, National Ready Mixed Concrete Association. Steve Parker is vice president, aggregate development, RMC Mid-Atlantic and chairman, ASTM Subcommittee 09.40, Ready-Mixed Concrete.