A new test method developed by ASTM International Committee C01 on Cement provides information about the behavior of cement that can be used in the process of selecting cementing materials for specific applications. The standard, C 1608, Test Method for Chemical Shrinkage of Hydraulic Cement Pastes, is under the jurisdiction of Subcommittee C01.31 on Volume Change.
Test Method C 1608 was developed to provide a measure of early age hydration. Existing methods, such as C 186, Test Method for Heat of Hydration of Hydraulic Cement, only provide values after seven or 28 days of hydration. However, it was important to develop a standard that dealt with hydration that occurs sooner than that because early age hydration is critical for strength development and to prevent cracking due to thermal and autogenous (and drying) shrinkage stresses. During early age hydration, the chemical shrinkage is in direct proportion to the amount of hydration that has occurred.
"The measurement of chemical shrinkage provides a valuable indication of the initial reaction rates of the cement paste being evaluated," says Dale Bentz, chemical engineer, Building and Fire Research Laboratory, National Institute of Standards and Technology. Bentz says that information gained from the use of C 1608 could be used to infer early age performance with respect to thermal properties (heat release and temperature rise) and cracking (autogenous shrinkage). He also notes that the test method could be used to evaluate the influence of chemical admixtures, such as accelerators and retarders, on early age hydration rates.
The measured chemical shrinkage also directly indicates the amount of necessary curing water (either external or internal) that must be supplied to maintain complete saturation of the capillary pores within the hydrating cement paste. This is particularly valuable for mixture proportioning for internal curing.
Bentz credits Mette Geiker, currently a professor at the Technical University of Denmark, for doing the pioneering research (as part of her Ph.D. thesis) on which Test Method C 1608 is based.
Interested parties are invited to participate in revisions of C 1608. In addition, the subcommittee is seeking participants for a round robin interlaboratory test to establish the multi-laboratory precision of the test method.
For further technical information, contact Dale Bentz, Building and Fire Research Laboratory, National Institute of Standards and Technology, Gaithersburg, Md. (phone: 301/975-5865; email@example.com). Committee C01 meets Dec. 7-9, in Dallas, Texas. For membership or meeting details, contact Jim Olshefsky, ASTM International (phone: 610/832-9714; firstname.lastname@example.org).