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Determination of the portland cement content of hardened concrete is often a matter of concern to engineers and chemists working with mortars and concretes. Unfortunately, a precise method of analysis has not been developed due to the many complexities of the material under test. Difficulties include the selection of representative samples, the presence of aggregate materials from unknown sources, the use of portland cements that differ substantially from an average composition, the presence of admixtures or additions (such as pozzolans or finely ground slag), the degree of hydration of the cement, the effect of carbonation as contrasted with hydration, and the effect of leaching of the concrete. In view of such formidable obstacles, chemical procedures demand that every effort should be made to obtain samples of the materials used in the concrete mixture. Where adequate information is obtained on the coarase and fine aggregate and cementing material, a reasonably accurate estimate of the cement content of hardened concrete can be made by chemical methods. In the absence of sufficient information on the source materials, assumptions must be made with respect to the amount of soluble substances that may be contributed to the analysis by the aggregate fractions and with respect to the ratio of aggregate materials present in the mixture. The assumptions affect the reliability of the test results. In some instances, the use of several schemes of analysis should be considered since the information derived from one method may assist in interpreting the results derived from an alternate method. This report outlines several methods that have been employed to determine the cement content of hardened concrete and indicates the reliability of the results that have been obtained, with emphasis being given to the procedure that is available as ASTM Test for Cement Content of Hardened Portland Cement Concrete (C 85). Results of cooperative tests undertaken by ASTM Committee C-9 to evaluate the reliability of the ASTM method of test are presented.
Minnick, L. J.
Vice-president in charge of research, Or. & W. H. Corson, Inc., Plymouth Meeting, Pa.