PORTLAND CEMENT. Portland cement is the product obtained by finely pulverizing clinker produced by calcining to incipient fusion an intimate and properly proportioned mixture of argillaceous and calcareous materials with no additions subsequent to calcination excepting water and calcined or uncalcined gypsum.
The old Roman cements were natural cements or were a mixture of slaked lime and volcanic dust which was found in large quanti ties in Italy. Indications are that concrete was prepared much as it is to-day and even this com bination which is crude in comparison with the modern portland cement concrete produced•an artificial stone which has stood the test of time. There is a gap of about five centuries between the Roman times until the next record of the use of cement. In 1756 John Smeaton, an engineer who construoted the Eddystone light house in the English Channel, while searching for a suitable mortar discovered that an im pure limestone containing a certain amount of clayey matter possessed decided hydraulic prop erties when calcined or roasted.
These early natural cements were very dif ferent from modern cements, however. It was necessary to use rocks with the proper propor tion of material in their makeup and any varia tion in the composition could not be regulated since the nature of the material was not under stood.
Portland cement originated with Joseph Aspdin, a bricklayer of Leeds, England, who in 1824 took out a patent for a cement to which he gave the name of "Portland° on account of its resemblance when hardened to the famous stone used extensively for fine building and found on the Isle of Portland on the northern coast of England. It is interesting to note that about a quarter of a century later came one of the earliest recorded uses of the modern rein forced concrete construction in the building of a reinforced concrete rowboat by M. Lambot, near Carces, France, which is the forerunner of the modern concrete ship.
In his patent, Aspdin signified that definite amounts of clay and limestone be used and described a process of putting these two ma terials together, then calcining them in the manufacture of his Portland * cement. This is the distinction between natural and portland cements. As one writer has said, *A natural
cement is a gift of Nature depending as it does upon Nature for the proper materials cor rectly proportioned for the manufacture of cement. A portland cement is a manufactured product, its composition being governed at all times by the proper selection of raw materials of which it is made, and any variation in the composition of these raw materials is easily de tected and it is, therefore, a highly dependable product." The history of the commercializing of port land cement is a history of inventions and im provements in its manufacture. In this, Ameri can engineers and inventors have had remark able success, for although this country was one of the last to begin the production of portland cement the output to-day has far outstripped that of Europe.
Aspdin's portland cement was found greatly superior to the Roman cement, Puzzoulana cement and hydraulic lime previously used and its manufacture extended rapidly, especially in England and Germany. In this country it was first successfully made at Coplay, Pa., in 1878 but until 1890 practically all the portland cement used in this country was imported from Europe. After that date the industry increased with great rapidity until the United States ranks as the chief cement producing country of the world. From a production of 42,000 barrels of portland cement in 1880, the annual output in the United States rose to nearly 93,000,000 bar rels in 1917.
Modern portland cement is manufactured from a mixture of two materials, limestone rock or similar material like chalk or marl which is nearly pure lime and another material supplying the other ingredients needed which is usually shale or clay although blast furnace slag is also used in conjunction with limestone. The one supplies the calcareous materials and the other the argillaceous or clayey materials. It is essential that the mixed raw materials contain certain exact percentages of these ingredients; this proportion differs slightly with different materials but ranges generally 75-80 per cent of carbonate of lime to 25-20 per cent of anhydrous clay.