The National Academies

NCHRP 10-25A [Completed]

Instantaneous Determination of Water-Cement Ratio in Fresh Concrete

  Project Data
Funds: $300,000
Research Agency: Wiss, Janney, Elstner Associates, Inc.
Principal Investigator: William G. Hime
Effective Date: 6/1/1985
Completion Date: 2/15/1990

This project investigated the application of analytical instrumentation and procedures to the rapid determination of water:cement ratio of fresh concrete. Attempts were made to develop a single "probe" that could be inserted into the fresh concrete and uniquely provide its water:cement ratio. The probe involved the use of specific ion electrodes capable of measuring the concentration of ions dissolved from the cement by the concrete mix water. Because of "poisoning" of the electrodes and occasional unexplained variances, this approach was abandoned. The work, however, suggests that such an approach may prove fruitful as instrumentation improves.

Other procedures for the separate determinations of water and cement were, however, pursued and found capable of providing data for calculation of water:cement ratio within ten minutes. Water is determined by a microwave technique employing a special ashing block assembly that allowed a determination of total water in one minute. The water determined includes that due to aggregate absorption, but the sample is chosen to minimize aggregate absorption to a level that can generally be ignored.

A second method involving use of a bromide specific ion electrode does not require a power source and its use could improve the Kelly-Vail procedure often used for water content determinations. This method primarily provides a net water content.

Cement is determined by a specially developed colorimetric procedure for soluble silica.

Research is complete. Research Results Digest No. 174, "Determinations of Water:Cement Ratio in Fresh Concrete," has been published, and it summarizes the research effort. The agency's complete final report was also distributed to all state DOTs.

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