Calculation of Compounds in Portland Cements

The National Bureau of Standards–National Institutes of Standards and Technology has had an illustrious history of research on the most widely-used, man-made materials of construction, cement and concrete—materials which are often taken for granted, because of their commodity nature and generally successful use in the structures that comprise about 80 % of the Nation’s fixed wealth. The level of NBSNIST’s cement and concrete materials research effort, in contrast to its structural research effort, has varied substantially over the century, with two highly productive periods separated by an almost dormant period from about 1960 to 1980. While some important contributions were certainly made prior to 1924, an outstanding period stretched from 1924 to 1954 when a strong NIST cement research program was complemented by an equally strong and synergistic industrysupported program, the Portland Cement Association Fellowship at the National Bureau of Standards. The Director of the PCA Fellowship for the whole of its 30-year life was Dr. Robert Bogue, a major figure in the history of cement research. Robert Herman Bogue, a physical chemist, was born in Southborough, Massachusetts, on September 27, 1889. Before taking the position as Director of the PCA Fellowship in 1924, he had obtained degrees from Tufts University (B.S., 1912), Massachusetts College (M.S., 1915), and the University of Pittsburgh (Ph.D., 1920), and had gained professional experience as an Assistant Professor at Montana State College, 1915-17, a Fellow of the Mellon Institute, 1917-22, and an Associate Professor at Lafayette College, 1922-24. His research interests at that time appear to have been the chemistry of gelatine and the colloidal behavior of proteins— subjects remote from the inorganic materials that would be central to the rest of his professional career. As Director of the PCA Fellowship, Bogue exercised a remarkably far-sighted leadership that made the Fellowship a major contributor to what would now be described as the materials science of concrete. Among Bogue’s personal contributions was a landmark paper, Calculation of Compounds in Portland Cement [1], published in 1929. To understand the significance of the paper, it is necessary to know a little about portland cement and its manufacture. Portland cement was invented in 1824. Its essential ingredient is cement clinker, a granular product from the high temperature (~1500 C) processing of an appropriately proportioned, finely-ground mixture of minerals that are sources of the common oxides CaO, SiO2, Al2O3, and Fe2O3; (for convenience in this paper, and in accord with cement industry usage, these oxides will frequently be referred to by the single letters C, S, A and F, respectively). Typical raw materials that are sources of these oxides in clinker production are, in the same order, limestone, quartz sand, clay, and iron ore. The cement manufacture ends with the intergrinding of clinker with a mass fraction of about 5 % gypsum (CaSO4 2H2O) to produce the fine cement powder, usually gray in color, of which almost 100 million tonnes (1 tonne = 1000 kg) are produced in the U.S. each year. (The gypsum is added to control the rate of setting of the cement.) Until the publication of Bogue’s paper, there was much controversy about the compositions of the compounds present in the clinker, even though the elemental compositions of clinker and cement (always expressed in terms of simple oxides) were determined routinely in cement plants and other laboratories. Publication of the paper obviously met an objective Bogue had set for the Fellowship since, in the text of an address given to the American Concrete Institute [2] two years earlier in 1927, he wrote: “ . . . this is an age of advancement. The cry for new knowledge is in the air. . . . . Questions are being asked now in all seriousness which a few years ago would have been regarded as absurd because unanswerable. . . . . All of this brings us to the belief that an unraveling of the laws governing the constitution of cement clinker and the behavior of the constituents of cement when made into concrete may hold developments which today can only be sensed but not definitely apprehended.” In the same address, he made the nature of the problem to be solved clear by saying, “Of fundamental importance, above all others, and for the reasons given above, are the studies which will give us information of the nature of the constituents in clinker. Some of these have been known for some time. Others have been guessed at, but the guesses of the various authorities do not always agree. One group believes that a complex compound containing lime,