CEMENT. A cement is any compound which, under certain conditions, is plastic and under others develops tenacity and can be used for holding together various materials; hence glue, lime, asphaltum, mucilage and solder are cements. By far the most important class of cements structurally and commercially are the hydraulic cements, compounds of lime, silica and alumina that have the property when mixed with water to a paste of cohering or setting and finally becoming stone hard, even under water. The hydraulic cements may be divided into four classes based on differences in the mate rials used. The setting is probably due to the same general chemical reactions in all hydraulic cements; the silicates and aluminates formed in burning take up water and are converted into hydrated calcium silicate and aluminate and crystalline calcium hydrate. The quickness with which these reactions take place vary, the composition of the original materials and the differences in the methods of manufacture being the controlling factors. Quick-setting cements may become hard in a few hours, while some slow-setting cements require many months to reach their maximum tenacity.
The four classes of hydraulic building ma terial above mentioned are: (1) Hydraulic lime made from a limestone containing a small proportion of clay (8 to 10 per cent) by burn ing at a low temperature and slaking the burned rock with water. (2) Hydraulic or natural-rock cement made from a limestone containing a relatively high proportion of clay, by burning at a low heat and grinding the product to powder. (3) Portland cement made from an artificial mixture of carbonate of lime (either chalk, limestone or marl), with a cer tain proportion of clay, burning at a white heat and grinding the clinker topowder. (4) Pozsuolana or slag cement made by mixing some kinds of finely-ground scoria (volcanic ash) or blast-furnace slag with a small pro portion of slaked lime. Of these the second and particularly the third are of chief import ance in this country, though the manufacture of slag cement is a promising industry.
The manufacture of hydraulic lime, though carried on to a considerable extent in France, has never been established in this country, probably owing to the abundance of excellent cement-rock in New York, Pennsylvania and other States. Hydraulic lime is light and bulky compared with the other cements. It re quires from one to several days to set and hardens slowly, but some grades resist the con tinued action of sea water even better than Portland cement.
This material, also known as common cement, hydraulic cement, Rosendale cement and quick-setting cement, is manufactured in considerable quantities in some parts of the United States. It is made also in France, but the German and English output has been insignificant for someyears. In the United States the material used is limestone, often containing over 23 per cent of clay, and the limestone is generally dolomitic, that is, contains carbonate of magnesium. In Europe magnesian limestones are seldom used. The cement rock is quarried, broken and burnt in continuous kilns, much as limestone in the manufacture of ordinary lime. The burnt rock is a mass of partly vitrified clinker not af fected by water. It is ground in mills of sev
eral types. Formerly all plants used millstones, and the light yellowish or brownish powder, fine enough to pass a 50-mesh screen, is sent to market in barrels containing about 300 pounds, or in sacks. When mixed with water this cement sets in a few minutes and hardens gradually. It is cheap and when mixed with one part of sand by weight is used for mortar or concrete and for cistern and reservoir lin ings. It has not the great tensile strength of Portland cement, hardens slower and more im perfectly.
The composition of Rosendale cement rock and natural hydraulic cement is as follows: Carbonate of lime 45.91 Carbonate of magnesia 26.14 Silica and insoluble 15.37 Sesquioxide of iron / 11.38 Alumina Water and undetermined 1.20 100.00 Silica 22.75 Alumina and iron sesquioxide 16.70 Lime 37.60 Magnesia 16.65 Alkalis Carbonic acid 5.00 Sulphate of lime } 1.30 Water Total 100.00 The chief centre of the industry in this country is the Rosendale district of Ulster County, N. Y., where the rock quarried is a limestone of the lower Helderberg series. It is also made in Pennsylvania, the Louisville region of Kentucky and Indiana, at several points in Illinois and around Milwaukee, Wis. The natural or Rosendale cement industry has weakened since 1903, and the production is now comparatively small.
The total production of Port land cement in the United States in the year 1916 was 91,521,198 barrels, valued at $100, 947,881, an increase over the 1915 figures by 6.5 per cent in amount, and 36.6 per cent in value. The shipments from the mills for the year, however, were 3,031,098 barrels more than the production — from the reserve stock left over from the previous year. The price ob tained by the mills varied from 94 cents per barrel in eastern Pennsylvania to $1.64 per barrel in Utah. (These figures do not in clude the barrel or bag in which the cement is marketed). The production was pretty well distributed over the entire wuntry, but the output in the so-called Lehigh district, com prising eastern Pennsylvania and western New Jersey, was notably larger in proportion, amounting to nearly 30 per cent of the whole. The reserve for another year's supply left at the mills at the close of 1916 amounted to 8,360,478 barrels.
Of natural cement and puzzolan cement the production in the United States in 1916 amounted to 842,137 barrels, valued at $430,874 — an average of 512 cents per barrel. Only one puzzolan plant (at Birmingham, Ala.) was active during the year.
Consumption.— The total consumption of cement in the United States is arrived at by adding the shipments from the mills to the imports for the year, and subtracting the ex ports. On this basis the 1916 consumption ap pears to be 91,990,156 barrels-7,621,288 bar rels (about 9 per cent) more than in 1915. The highest per capita consumption for the year was that of Iowa, 1.77 barrels. Following this were Michigan with an average of 1.58 barrels and California with 1.51 barrels. In 17 of the States the consumption exceeded one barrel per capita, due in large part to extensive con struction of public works in those States. See CONCRETE; LIMESTONE; MINERAL PRODUCTION OF THE UNITED STA rES; PORTLAND CEMENT.