![]() ![]() ![]() basis and plotting the result, the point will fall outside of the area mentioned and different compounds may be expected to occur, some of which may be non-hydraulic. If, however, the difference in percentage composition is great enough, on recalculating the percentage of the three constituents (SiO2, Al2O3, CaO) to a 100- per-cent. Differences in the percentages of lime, silica, and alumina, within certain limits, do not cause the appearance of a fourth and new compound they merely change the proportion between the three compounds mentioned this is an important point. Al2O3, and dicalcium silicate (or calcium orthosilicate), 2CaO.SiO2, beta modification. Points thus plotted will fall within a restricted triangular area within the diagram, with three compounds forming the apices of the small triangle viz., tricalcium silicate, 3CaO.SiO2, tricalcium aluminate, 3CaO. Perfectly sound Portland cement has been made of these three constituents alone hence if the percentages of these constituents are recalculated to a basis of 100 per cent., neglecting the ferric and other oxides that are always present in small amounts, the resulting percentages may be plotted on the ternary concentration diagram. are sometimes found.Ī long series of studies on the ternary system, lime-silica-alumina, and the system alumina-silica-magnesia, as well as studies of binary systems of the same components, by physicists, physical-chemists and chemists of the Geophysical Laboratory, the Bureau of Standards, and different universities, and a comparison study of Portland cements has shown quite definitely that the three constituents that form the bulk of normal Portland cement-lime, CaO, silica, SiO2, and alumina, Al2O3-exist as fixed components with definite chemical composition and constant optical properties.Ī study of the analyses of standard brands of normal Portland cement will show that their percentages of lime, silica, and alumina amount to over 90 per cent. Both potash and soda exist to a small degree detect flakes of quartz from the ball mills, metallic iron from the mac u particles of semi-fused coal ash from the fuel, etc. ![]() The magnesia, MgO, is in a state of solid solution the other components and is apparently without much effect in the quantities found in cements. In the order of their cementing qualities these are Tri-calcium silicate, 3Ca0.SiO2, tricalcium aluminate, 3CaO.Al2O3, trical ferrite, 3CaO.Fe2O3, and calcium orthosilicate, beta form, 2CaO.Si In addition, there is a certain quantity (generally about 3 per cent.) gypsum. Normal Portland cement is composed of mechanical mixtures of definite chemical compounds having constant chemical and physical properties. Petrographic, by the method of immersion, and by making thin sections from test pats of both neat cements and standard-mortars. These fractions may be further studied chemically and petrographically and micrometric measurements made of the grains. Mechanical, by determining the fineness with the air analyzer, which separates into fractions of various grain dimensions all of that portion which in the ordinary sieve test passes the 200-mesh sieve and constitutes at least 75 per cent, of the total cement. Chemical, by determining quantitatively not only the usual constituents, but the carbon dioxide and water. The most promising method of attack makes use of chemical, mechanical, and petrographic methods. It is likewise essential to know the character, behavior, and composition of the hydration, products of Portland cement. The solution of this problem involves a knowledge of the chemical composition of Portland cements, also of their constitution (or componential composition), as the behavior of a cement, when gaged, is dependent on the physical and chemical characters of the compounds of which it is composed, the proportions existing between them, and the fineness of grinding. The problem is to find a simple, usable easily applied method that will supplement the standard tests. In these cases, the origin of the trouble must be sought in the cement, therefore some additional mode of determining the quality of cement must be employed. Such failures occur even when proper methods of mixing and placing have been used and where weather conditions were correct. The failure, or disintegration, of concrete in structures, even when the cement, sand, and coarse aggregate used have passed satisfactorily all tests and inspections, is not uncommon.
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