【国外标准】 Standard Practice for Evaluating Early Hydration of Hydraulic Cementitious Mixtures Using Thermal Measurements

5.1 This practice provides a means of assessing the relative early hydration performance of various test mixtures compared with control mixtures that are prepared in a similar manner.5.2 Thermal profiles are used to evaluate the hydration behavior of hydraulic cementitious mixtures after the addition of water. They may provide indications concerning setting characteristics, compatibility of different materials, sulfate balance, relative heat of hydration, and early strength development. They can be used to evaluate the effects of compositions, proportions, and time of addition of materials as well as the initial mixture and test temperatures. Thermal profile testing is an effective tool for identifying performance sensitivities or trends, and may help to reduce the number of concrete test mixtures required to develop and qualify mixtures, especially those to be subject to variable ambient environments. It may be used by concrete producers, materials suppliers, and other practitioners to support mixture development, selection of material types or sources, optimization of proportions, or troubleshooting of field problems.5.3 This practice can be used to understand concrete problems related to slump loss, setting, and early strength, but results may not predict field concrete performance. Performance verification with concrete is needed to quantify the trends identified using thermal testing.5.4 This practice can be used to evaluate the effects of chemical admixtures on the thermal profiles of cementitious mixtures. This can be especially useful in selecting dosages appropriate for different ambient conditions.5.5 Thermal measurement testing as described in this practice may have similar significance and use as isothermal calorimetry described by Practice C1679 or some types of near-adiabatic calorimetry. The selection of which practice or methods to use may depend on specific applications and circumstances. The thermal profiles obtained by this practice may have similar shapes to isothermal hydration profiles as obtained by Practice C1679, but thermal profiles from this practice do not provide quantitative measurement of heat of hydration, are affected by various details of the test conditions and mixtures (see 3.2.10 and the Appendix), and are subject to greater variability. Equipment used for this practice is less expensive than isothermal or near-adiabatic calorimeters and may be more easily adapted for use in the field or where a large number of different specimens and mixtures must be evaluated in a short time period. Identification of the sulfate depletion point of a mixture (as described in Practice C1679) is not generally possible using thermal measurement testing.5.6 To evaluate the potential for abnormal hydration, it is important that the test temperatures and the initial temperatures of the mixture be selected to represent the range of expected initial concrete field temperatures.5.7 This practice is not intended to provide results that can be compared across laboratories using different equipment nor to provide quantitative measurements or corrected approximations of actual hydration heat. It should not be cited in project specifications or otherwise used for the purpose of acceptance or rejection of concrete. It is intended to serve as a simple and expedient tool for comparison of the relative early-age hydration performance of different specific combinations of materials that are prepared and stored under the same conditions.1.1 This practice describes the apparatus and procedure for evaluating relative differences in early hydration of hydraulic cementitious mixtures such as paste, mortar, or concrete, including those containing chemical admixtures, various supplementary cementitious materials (SCMs), and other finely divided materials, by measuring the temperature history of a specimen.1.2 Calorimetry is the measurement of heat lost or gained during a chemical reaction such as cement hydration; calorimetric measurements as a function of time can be used to describe and evaluate hydration and related early-age property development. Calorimetry may be performed under isothermal conditions (as described in Practice C1679) or under adiabatic or semi-adiabatic conditions. This practice cannot be described as calorimetry because no attempt is made to measure or compute the heat evolved from test specimens due to hydration, but it can in many cases be used for similar evaluations. Variables that should be considered in the application of this practice are discussed in the Appendix.1.3 Units—The values stated in either SI units or inch-pound units shall be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in non-conformance with the standard. Some values have only SI units because the inch-pound equivalents are not used in practice.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.NOTE 1: Warning: Fresh hydraulic cementitious mixtures are caustic and may cause chemical burns to skin and tissue upon prolonged exposure.21.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.