Thank you for correcting the text in this article. Your corrections improve Papers Past searches for everyone. See the latest corrections.

This article contains searchable text which was automatically generated and may contain errors. Join the community and correct any errors you spot to help us improve Papers Past.

Article image
Article image
Article image
Article image
Article image
Article image
Article image
Article image
Article image
Article image
Article image
Article image

CEMENT: ITS DISCOVERY AND MANUFACTURE.

(By J. Bboitgh Stansell.) The most important ingredients required for the fabrication of a good Portland cement, when truly combined, are carbonate of lime, silica, and alumina. It is seldom, however, that these leading and indispensable minerals are found in such a state of chemical purity as to be accepted without careful analysis. In the early days of its manufacture London was chosen as the proper centre for the establishment of the new venture, as it commanded all the conditions required tor success. The chalk formation on the banks of the rivers Thames and Medway, and the deposits of mud in their estuaries and creeks furnished, at an inconsiderable cost, the most suitable supplies in the best and most acceptable form. Fuel was readily obtained in the shape of coke from the gasworks of the Metropolis, and the port of London with its numerous shipping facilities, affoided the means of exporting the cement to the distant countries on the most advantageous terms. These very favorable and singularly fortuitous circumstances resulted in the establishment of extensive cement manufactories in the neighborhood of London, which is now regarded as the centre and largest field of this industry. Chalk and clay are the materials used on the Thames and Medway, at Boulogne, and at Stetten, in North Germany ; limestone and clay at Bugby and Stockton, in Warwickshire, Bridgewater in Somerset, Poole and Wareham in Dorset. The strength of cement depends in a great measure upon the right proportions between the chief constituents being observed in its manufacture. If the lime be in excess the cement has a tendency to crack and blow, especially it not sufficiently burnt or finely ground. If the clay be in excess the cement will be permanently weak, will have a buff color when made up neat and exposed to the air, and to some extent have the character of Boman cement. The burning is in kilns of different forms, the best combining thorough and uniform calcination. Both coal and coke are used as fuel. In Germany the Hoffman kiln is much used. The material, when burnt, termed “ clinker,” has to be broken in small pieces and ground, like flour, between millstones. It is ground finer in Germany than, in England. The standard of fineness recognised throughout Germany and Austria is that the residue must not exceed 20 per cent, on a sieve of 5000 meshes per square inch. In practice the principal manufacturers supply cement so fine that the residue does not exceed 10 per cent.—ln England the residue would be from 15 to 27 per cent with a sieve of 2580 meshes per square inch. The coarser part, which is generally the hardest and most highly burnt, when not finely ground has hardly any cementitious value, and may be left out without much, if any, diminution of strength, the waste therefore is enormous; but if finely ground this coarse part becomes the best. The proportion of lime used in the manufacture would depend upon the particular kind of work it was intended for. For stuccoing purposes about 72 per cent of carbonate of lime would be a fair proportion, but for engineering work a denser cement would be required. With a larger proportion of lime and a higher degree of calcination, it would be more resistant in its character. The first impulse to the more extended use of Portland cement may be traced back to the period when English engineers began to institute the careful and accurate tests of the quality of the cement supplied for works of importance. Thus it was not until Messrs Bcndel and Druce, and more especially Mr Grant, had ■established the fact that Portland cement of a specified weight and density could be depended upon to undex’go certain definite tests, that reliance ! ' ’ 1 ' i the new TrrHrial. in the n ? of buildir ;v..« --rial, u olished Tno adir... : e:

cement supplied for the main drainage works of London, carried out for the Metropolitan Board of Works by Mr John Grant, Member of the Institute of,'Civil Engineers* between the years 1859-1871, and communicated to the Institution of Civil Engineers in 1865 and; 1871, constitute the basis of an accurate knowledge of the behaviour of Portland cement, and since Mr Grant’s observations the records of Messrs Colson, Mann, and numerous other observers, have increased the store of ; information concerning the strength and characteristics of Portland cement. It is impossible to doubt the adoption of certain rigidly imposed tests of quality has been of the utmost advantage in improving the manufacture, and in ensuring the excellence of Portland cement. The plan of manufacture employed by the earlier makers in tbe Thames district has -been followed with but trifling modifications, by all the manufacturers up to within a few years of the present time. Recently, however, several important changes have taken place, and the introduction of these processes, by some of the leading firms, has, so to speak, revolutionised the manufacture.

The growth of the use of Portland cement has been influenced by the improvements in its manufacture. Originally intended as a plaster or mortar in connection with housebuilding purposes, its success in that direction gave but faint indication of its ultimate usefulness. When engineers became impressed with its useful properties, and the reliability of its quality its sphere became enlarged to such an extent and with such rapidity, that for some time the demand exceeded the supply, so much so in some cases as to interfere with the profitable progress of important works at home and abroad. The harbor and dock works of England and breakwaters &c., of the colonies may bo regarded as important ai d extensive applications of Portland cement. Many of Ihc-iO valuable structures were impossible befo e the invention of this useful material. The harbor works at Douglas in the Isle of Man, afford a good example of concrete work, built under the direction of Sir John Goode, who has perhaps the largest experience in such works amongst English engineers. The extensive Government works at Dover harbor have been for many years constructed of concrete blocks. It .is now a question of increasing the size of the blocks to be used. in more than ordinarily exposed situations. There is none of the material used in building which requires a more accurate knowledge of its properties than Portland cement, yet its pecularities, and its chemical and physical characteristics, receive but slight attention. It is unsafe for the builder or contractor to repose too confidently in the name by which it is sold, or the merits which its purveyor represents it to possess. The only means of securing proper cement is by testing it by the proper machinery, made for this purpose, and in some cases by a chemical analysis to ascertain the proportions of Ume and clay &c. The test as at present applied is as follows ;

It shall weigh not less than 1121bs to the imperial (striked) bushel. At the time of delivery, samples to be taken from one sack in ten, and made into brignettes, as soon as set to be placed in water for seven days, then taken out and tested for breaking power, viz to bear a tensile strain of 6501bs upon the test Hocks inch by inch in section. The cement to pass through a seive of 50 meshes to the lineal inch. This is part of the specification under which Portland cement is supplied to the military works at Chatham. In New Zealand the weight per bushel is higher being Hslbs per bushel, and the tensile strain 7501bs and upwards. The seven days test is hardly sufficient for submarine works; it should be supplemented by a test at the expiration of twenty-eight days as confirmatory or otherwise of the seven days test. There has been a growing tendency on the part of engineers to insist upon a very heavy cement. Tins has been met by the manufacturer by overburning the clinker, which then is exceedingly difficult to reduce to a powder of the requisite fineness. Such cement, unless reduced so as to pass 50 meshes to the lineal inch, becomes of a very inferior character, and although bearing a very high tensile strain, is likely to result in disappointment and probable loss, unless submitted to and passing the sieve test with a refuse of not more than ten per cent. In Germany, the Committee of the Association of Engineers have adopted a sieve of 5806 meshes to the square inch and allowed a residue of twenty per cent. There is a great diversity in the tensile strain of the same cement tried by different persons. This can only be accounted for by the fact that the same conditions are not observed by each person In mixing the cement it undergoes a chemical process of crystallization when a small excess of water will alter the results materially. When a cement will not pass the required test an analysis would at once shew the weak point; the fact of being able to do this would deter importer from sending out an indifferent article. Portland cement has become so important a constructive material, and its co'st now forms so large an item in engineers’ estimates, that in many cases it would prove highly beneficial to make the cement on the site of the works or in their immediate neighborhood, In many cases this is not only possible, but, generally speaking, if the quantity of cement required is at all considerable, and especially in foreign works, it would result in much advantage. Within a few miles of Timaru the materials can be found, it is believed, for making Portland cement. It is hoped that these brief articles may help to draw attention to this important article and also assist those workers who have so much to do with Portland cement. • The writer of these articles is indebted to a work on Portland cement by Henry Beid, C.E., for many of the facts stated herein.

Tiers, tiers, idle tiers,” as the actor said when lie saw the rows of empty benches before him. Lord Oranmore and Browne a prominent landlord in the County Mayo, and who has made himself obnoxious to the Land League by letters in the Press which he has written on the Irish land question, has more than onco had his life threatened. Mark Twain once drew up a comic almanac of Californian weather, in which the predictions varied mainly from “ severe earthquakes ” in January to “ mild and balmy earthquakes ” in July.

Permanent link to this item
Hononga pūmau ki tēnei tūemi

https://paperspast.natlib.govt.nz/newspapers/SCANT18810506.2.10

Bibliographic details
Ngā taipitopito pukapuka

South Canterbury Times, Issue 2535, 6 May 1881, Page 2

Word count
Tapeke kupu
1,759

CEMENT: ITS DISCOVERY AND MANUFACTURE. South Canterbury Times, Issue 2535, 6 May 1881, Page 2

CEMENT: ITS DISCOVERY AND MANUFACTURE. South Canterbury Times, Issue 2535, 6 May 1881, Page 2

Help

Log in or create a Papers Past website account

Use your Papers Past website account to correct newspaper text.

By creating and using this account you agree to our terms of use.

Log in with RealMe®

If you’ve used a RealMe login somewhere else, you can use it here too. If you don’t already have a username and password, just click Log in and you can choose to create one.


Log in again to continue your work

Your session has expired.

Log in again with RealMe®


Alert