Portland cement

“ Here, and above Rochester Bridge, the pleasant Medway valley is scarred and seamed with the chalk-quarrying and the mud-dredging that go towards the making of Portland cement, this neighbourhood being one of the chief centres of that industry. The chalk and the river-mud are mixed roughly in the proportion of three parts of chalk to one of mud, and are then burnt in kilns and ground into a flour-like powder. Portland cement, invented about 1826, is an important industry, with an output of over 3,000,000 tons a year in this country. ”

“ All this expansion of an old art has been stimulated by a steady reduction in the price of Portland cement, and by constant improvement in its quality. As the manufacture has expanded, its standards have risen, its machinery has become more economical and trustworthy in results. While the cost of concrete has thus been lowered by a fall in the price of cement, the wages of bricklayers and stone-masons have advanced, adding a new reason for building in concrete, since it requires in execution but little skilled labor. The good points of concrete are manifold ”

“ Experience shows that, although spherical pebbles are to be avoided, Portland cement adheres tightly to smooth flint surfaces, and that rough stones often give a less compact concrete than smooth ones on account of the difficulty of bedding them into the matrix when laying the concrete. In mixing concrete there is always a tendency for the stones to separate themselves from the sand and cement, and to form “pockets” of honeycombed concrete which are neither water-tight nor strong. These are much more liable to occur when the stones are flat and angular than when they are round. ”

“ The first of these is Portland cement, which has sprung into very general use, not only for work where extra strength and durability are required, and for underground work, but also in general building where a small extra cost is not objected to. Ordinary lime mortar may have its strength considerably enhanced by the addition of a small proportion of Portland cement. Roman cement is rarely used for mortar, but is useful in some cases on account of the rapidity with which it sets, usually becoming hard about fifteen minutes after mixing. ”

“ Good Portland cement is so much stronger than any lime that there are few situations where it is not cheaper as well as better to use the former, because, although cement is the more expensive matrix, a smaller proportion of it will suffice for use. Lime should never be used in work exposed to sea-water, or to water containing chemicals of any kind. Portland cement concrete, on the other hand, may be used without fear in sea-water, provided that certain reasonable precautions are taken. ”

“ It is my opinion, founded on what I have seen and know, that Portland cement concrete is grand stuff when properly made; but you can't make the 'extra' profit on it you could, unless you can forget to rightly proportion the material. I mean leave out anything on the quiet you find is more profitable when it is absent; and now mixing machines are always used on works of importance where concrete is made in any considerable quantity, that is the only way you get a chance of a bit 'extra,' at least so runs my experience. ”

“ Soft, spongy foundations of natural cement or Portland cement of inferior quality are not only an inadequate support for the yielding surface, but they are easily penetrated by water from below and act as conveyors of water, while a sound and firm foundation of the best Portland cement concrete not only presents an unyielding support to the surface, but also, when properly set and dried before the surface is laid, keeps the surface as free as is possible under the circumstances from ground water, and thus contributes to the longevity of the surface. ”

“ At one time Portland cement concrete was considered to be lacking in fireproof qualities, but now it is regarded as one of the best fire-resisting materials known. Although experiments on this matter are badly needed, there is little Resistance to fire. doubt that good steel concrete is very nearly indestructible by fire. The matrix should be Portland cement, and the nature of the aggregate is important. ”

“ Portland cement is the best matrix known, since it is the most powerful and the most durable. It is used for mortar wherever great strength, hard-wearing properties, and resistance to damp are required. It should weigh 112 ℔ per striked bushel and be ground fine enough to pass through a sieve having 2500 meshes to the square inch and leave not more than 10% residue. Test briquettes after setting under water for seven days should stand a tensile strain of 350 ℔ on a square inch. It is used in the proportions of one part of cement to from one to five parts of sand. ”

“ It is asserted that a 1-4 fine sand mortar made with this cement is impervious. To use it the ordinary precautions adopted in the employment of Portland cement are necessary, and in addition the following: The cement must be mixed with moist instead of dry sand before the water is added; the sand should be clean, sharp and fine of grain; the mortar must be more perfectly mixed than ordinarily, and somewhat more water should be used than is ordinarily used. Perfectly even mixing is essential to the best results. ”

“ Cement is more expensive than brick. The surface to be covered should, first, be levelled, then saturated with water; after which is laid a three-inch bed of cement concrete, made of gravel, sand, and cement in proper proportions. Upon this is placed a three-fourth-inch layer of cement mortar. Ordinary American, hydraulic cement may be used for concrete, but for the three-fourth-inch layer nothing but best Portland cement should be considered. Sometimes the cement work in the cellar is done by the plasterer. Outside cement work for walks requires special skill. ”

“ The cement is made from the slag-sand, common lime, and iron oxides. It is little inferior to Portland cement in strength, while it does not cost one-fourth as much. The concrete made from this cement, mixed with the "shingle," is an excellent conglomerate for use in monolithic structures. It is stated by Mr. Charles Wood, in a paper read before the British Iron and Steel Institute, that "it took two good men, with steel bars and sledge-hammers, as much as four days to cut through a wall of this concrete about twenty-six inches thick." ”

“ Portland cement concrete can be hauled a considerable distance in a dump cart or wagon before it begins to harden; natural cement sets too quickly to permit of its being hauled far. Portland cement does not begin to set in less than 30 minutes. On a good road, with no long, steep hills a team will haul a loaded wagon at a speed of about 200 ft. ”

“ Where a very strong cement is needed for stone-work, it can be prepared by mixing a fine cement powder—e.g., Portland cement—with liquid silicate of soda. As it dries almost at once, it must be promptly applied. It is particularly well adapted for building under water, since it then becomes extremely hard. ”

“ Portland cement concrete if made with a non-porous aggregate is impervious to moisture, and yet at the same time, if not hydraulically compressed, will take up a sufficient quantity of moisture from the air to prevent condensation upon the surface of the walls. It not only resists the disintegrating influences of the atmosphere, but becomes even harder with the lapse of time. ”

“ This clinker is ground until it is reduced to a powder, and this is the Portland cement. Portland cement is generally mixed with an aggregate to produce strength and this aggregate is usually stone, gravel or sand. The third material needed to complete the combination is water.
SUCCESS IN THE USE OF CEMENT depends largely upon cement that is fresh. Cement is very sensitive to moisture and if kept where fogs, dew or moisture of any nature is absorbed into it, the first set or “hydration” takes place and destroys its use for fine handicraft. ”

“ The use of Portland cement in surface mixtures to be laid on streets of heavy travel, or those exposed to damp foundations, is very strongly recommended. On streets of the heaviest travel, or where the pavement will be exposed to unfavorable conditions of dampness, particularly if the pulverized stone is not very finely ground, the Portland cement may constitute twenty per cent. of the pulverized material, or “dust,” as it is commonly called. Ordinarily from five to ten per cent. may be used to advantage on all streets of moderately heavy travel. ”

“ I did not trouble myself about it then, but I do now, for I had a month or two in and about the testing places when there was no other job for me that suited, and I firmly believe almost all the failures of Portland cement concrete occur because the men that used it do not understand it, or the specification is not carried out, or is wrong somewhere. The best goods in the world want proper treatment, and, after all, the abuse of a thing is no argument against its use. Some quarry owners and stone merchants don't like cement concrete; it is poison to them, because it hurts their trade. ”

“ It may be well to observe here that in all works involving concrete foundations and paving in streets, the traffic should be entirely stopped if at all possible. Streets paved half at a time are never quite satisfactory, and the concrete should have at least a week to set before the pavement is placed upon it.
Upon a foundation of either Portland cement or bituminous concrete, the granite setts themselves should be grouted with a bituminous mixture instead of cement or lime grouting. ”

“ In foundations, according to the same authority above quoted, properly made Portland cement concrete may be trusted with a safe load of 25 tons per square foot.
In large masses concrete should be worked continuously, while in small masses it should be moulded in small sections, which should be independent of each other and simply form artificial stones. ”

“ At Concrete, a town of 1,200 people in Skagit county, two factories, employing 500 men, are daily turning out 1,400 barrels of Portland cement of fine quality, which is finding ready market in all the large cities. ”

“ Some piers in the Rosetta Barrage were therefore chosen for a similar experiment, but this time liquid Portland cement was used instead of clay, and the results were entirely satisfactory. Few discoveries have been of more signal service than the invention of Portland cement. It is not too much to say that it has revolutionized hydraulic engineering by the facilities it affords for constructing solid works in water. ”

“ Within the last few years, the cost of the best Portland cement has been so materially reduced that concrete has become an available material for the construction of factories. Unless used in great masses, however, it has not the strength to support the necessary floor loads without the use of steel reinforcement. As explained in [Pg 24] Design of Beams, the fibers on the bottom of all beams subjected to transverse stress are in tension, and while concrete has considerable resistance to compression, it offers comparatively little to tensile stress. ”

“ The State produces in value over half the total product of Portland cement for the United States. This industry is rapidly developing, the value of the product having increased from $3,142,711 in 1898 to nearly $6,382,350 in 1901. Some rock cement is also produced. Other products worthy of note are metallic paint, mineral water, salt, and ochre.
Agriculture. Farming is carried on more or less extensively in all sections, there being many arable and fertile valleys, even in the more mountainous regions. Districts too hilly to be readily cultivated are admirably adapted for grazing. ”

“ Concrete alone could not be used because of the excessive cost of the increased amount of Portland cement. It is said, that a retaining wall of all concrete would have cost about $600 per linear foot. Reinforced concrete costs about $58 per foot.
Steel is used, not merely as a reinforcement, but as the material of forms. Used thus, it may, at times, not only retain the concrete in position but also prevent the action of the surrounding soil or water. The possibility of using steel for forms depends largely upon the fact that many applications of concrete are becoming standardized rapidly. ”

“ Wilhelm Michaelis has found that Portland cement does not resist the chemical action of such water so well as do Roman cement and the hydraulic cements. The soluble sulphates in the sea water appear to enter into a substitution combination with the lime which exists in the cement in a free state or is liberated in the hardening, and it is converted into a sulphate, while disintegration ensues. In Roman cement the lime exists in combination, and there is no inclination toward the formation of a sulphate, and hydraulic limes resemble Roman cement in physical qualities. ”

“ If the sand is coarse and the crushed stone or gravel well graded in size of particles, it may be mixed in proportions of 1 part Portland cement, 21⁄2 parts sand, 5 parts gravel or broken stone. All proportions are measured by volume.
Bank run gravel is often used for sidewalk work, particularly where a good bank can be found on the farm. It is safer, if this material be used, to screen out the pebbles, using them as stone, measuring the quantities of stone and sand as described above. Concrete should not be laid in freezing weather. ”