15. Historical

It is said that as early as 1810 a patent was obtained in England for the manufacture of an artificial product by calcining a mixture of carbonate of lime and clay. This, however, was not called cement, and it was not until 1824 that Joseph Aspdin, of Leeds, England, in obtaining a patent for the manufacture of a similar material, called his product "Portland Cement." This name was probably suggested by the fact that the color of the hardened product resembled that of a limestone quarried on the Island of Portland. The industry was introduced into Germany about thirty years later, and has since grown to very substantial proportions in both of these countries, as well as in France, Austria, and Russia.

David O. Saylor was the first to manufacture Portland cement in the United States, at Coplay, Pa., about 1872, and works were established at that point in 1875. These were soon followed by other factories in Pennsylvania and Indiana, and at present cement is successfully manufactured in nearly half of the states of the Union, the production having steadily increased.

16. Materials Required

The materials requisite for the manufacture of Portland cement are carbonate of lime and silica. The former may be in the form of limestone, chalk or calcareous marl, while the latter may be in the form of clay or shale, or it may occur as an impurity in the limestone, as in the so-called "cement rock" of the Lehigh Valley region. The proportions required for ordinary materials are 25 per cent, clay or shale to 75 per cent, carbonate of lime. The cement rock worked in the Lehigh Valley region usually requires the addition of 10 to 20 per cent, of purer limestone, though in some deposits a small percentage of clay must be added. Some of the chief requisites for all Portland cement materials are that they shall be of uniform composition, and that they shall not contain such proportions of sulphur and magnesia as to give injurious percentages of these ingredients in the finished product. (§§ 50 and 52.) Formerly authorities did not agree as to whether the alumina in the clay or shale was an unwelcome constituent for Portland cement manufacture, but it is now generally agreed that the alumina, as well as the iron oxide, is useful as a flux in burning and that the dicalcic alumi-nate formed plays a role in the setting of the cement, and probably also in the subsequent hardening. If the ratio of silica to alumina and iron oxide falls below 2.5, however, the cement is likely to be too quick setting, while if this ratio exceeds 3 the mix is likely to be too refractory.

In regard to physical characteristics neither material should contain flinty nodules, difficult to crush and of a different composition from the main body of the rock. Marl should be as free as possible from hard shells, since their presence necessitates more careful preliminary grinding. Clay should not contain any considerable amount of coarse sand, for although silica is the most useful constituent of the clay it must not be in this insoluble form. In the highly argillaceous limestone known as cement rock, the mixing of the proper materials has been partially accomplished in nature, and with this material there is somewhat less danger from poorly proportioned mixtures than in dealing with practically pure carbonate of lime and clay or shale. The soft materials, marl and clay, have an advantage because they are usually of fine grain and easily reduced and mixed, but since they are so hygroscopic the expense of drying them may easily offset this advantage.

A few analyses of materials suitable for Portland cement manufacture are given in Table 4.

17. The materials for Portland cement manufacture, limestone, marl, clay, shale, etc., are widely disseminated, but the suitability of a certain locality for successful commercial manufacture depends upon the manner of occurrence of these requisites. In England the clay is dug from the old beds of the Thames and Medway Rivers, and chalk, which occurs in abundance, furnishes the carbonate of lime in most cases, though limestone is sometimes used. In Germany both chalk and marl are used; the chalk being a soft white marl similar to the deposits in this country, and the marl a "more or less hard limestone rock containing clay." In the United States both limestones and marls are used. The most important cement producing region in the United States is in the Lehigh Valley, where an argillaceous limestone is employed. The factories using marl are situated in New York, Ohio, Indiana, Michigan, etc., where the marl is found overlying or in the vicinity of beds of clay or shale suitable for cement making. In the Lehigh Valley region many advantages are combined. The cement rock of that locality has nearly the correct composition for Portland cement manufacture, requiring usually a small admixture of pure limestone. The supply of this rock is almost inexhaustible, the managers of the works have had long experience in the production of cement from these materials, and a market for the product is near at hand.

Table 4. Analyses Of Portland Cement Materials

Information collected from following sources: —

Cement Materials and Industry, Bulletin 243 U. S. Geol. Survey, by E. C. Eckel; Annual Reports, State Geological Surveys; and direct from companies.

Deposits of cement materials are of value only when the limestone or marl, and clay or shale, are found in large quantities and near together, when the physical character of the materials is such as to render them easy of comminution and mixture, when coal or other suitable fuel may be had at low prices, and when the market is not too far removed.

The following estimate of the relative quantities of cement made in the United States in 1903 from the several classes of materials has been made by Mr. E. C. Eckel:1

Argillaceous limestone and pure limestone...... 56 per cent.