The following is a transcript of an anonymous article that appeared in The Engineer, 109, 21/1/1910, pp 60-61, which is believed to be out of copyright. Although the article is anonymous, it was certainly written by Bertram Blount (1867-1921). Blount was retained as a consultant by the Collos Portland Cement Company, which was set up in 1907 by Edward John Vavasour Earle (1851-1923). He used his company, Martin, Earle and Co. Ltd, as a source of working capital. The purpose of the company was to acquire the 1905 patent of Heinrich Colloseus for an activated slag cement, then to sell world-wide licences to produce the cement, and to set up demonstration manufacturing plants. The underlying philosophy was a belief that, given the relatively large production (at the time) of slag as a zero-value waste material, the slag cement, produced at much lower cost, could completely displace Portland cement as a building material. The psychology of the promoters is demonstrated by the fact that, whereas the production plant described here cost £35,000, the value placed on the patent was £1 million. In addition to the grandiosity of the promoters' expectations, the article also demonstrates a persistent tendency of promoters of such products, to re-engineer the English language to make the product sound slightly less second-rate.
THE MANUFACTURE OF PORTLAND CEMENT FROM BLAST FURNACE SLAG
The great similarity in chemical composition existing between some types of blast furnace slag and Portland cement has long been recognised (Note 1), and has given rise to several attempts to utilise this waste product of the smelting works, so as to convert it from an encumbrance into a profitable source of trade (Note 2). The advocates of research in this direction maintain that the intense heat of the blast furnace brings about a complete fusion between the component substances of the slag, whereas the lesser heat employed in the ordinary kiln producing Portland cement is insufficient to do so. They hold that this incipient fusion of the latter process is a point of weakness in the system, the incomplete chemical combination resulting therefrom being regarded as the cause of numerous defects in the cement or mortar when used under certain conditions (Note 3). Thus the disintegrating effect of some alkaline liquids, of sea water, and of great heat is attributed by them to this cause. Again, the uneven coloration seen in some cements and the consequent stains produced on certain stones, such as marble, is due, they contend, to the non-union of the metallic salts in the cement with the other constituents.
Until lately, most attempts to transform the slag from blast furnaces into a commercially useful cement have resulted in failure. The "Puzzolan" cements of America (Note 4) are derived from this source, but their use is restricted in practice to cases where the cement or concrete after setting is kept moist, as in sea-water constructions, the thoroughly dry material being, we understand, found defective in strength.
Within recent years a new treatment for blast furnace slag has been designed by Dr. Heinrich Colloseus, of Berlin (Note 5). The results obtained, both commercial and technical, have been such as to induce several iron companies to adopt this method as a further aid to the economical working of their furnaces. In addition to this, the cement produced is said to compare so favourably to that obtained from the ordinary processes of manufacture that in some cases blast furnaces of a specially designed type have been erected for the purpose of producing the cement directly instead of its being produced as a by-product of iron smelting. The composition of blast furnace slag necessarily varies with the ores used, and it is only in those cases where the chief constituents are in a certain ratio that the process is possible. Thus a slag containing above 42 per cent. of lime and not more than about 37 per cent. of silica is suitable for the Colloseus method of cement production (Note 6).
In this country the Coltness Iron Company, Limited, Newmains, Lanarkshire, has acquired for the present the exclusive rights to work the process in Scotland (Note 7). In other countries several ironworks are employing it most successfully. At the Newmains works, which we recently visited to inspect the process as carried out there, considerable time has been given to perfecting the method and adapting its details to local necessities. The composition of the slag obtained from the hematite ores used at these works is as follows:-
The company has laid down an extensive plant for the economical production and handling of the slag cement. In addition to the actual producers and transporting arrangements a highly modern grinding mill has been erected and completely furnished testing houses laid down. In the accompanying engravings the extent of the plant will be seen.
The routine of the process is simple, although the chemical reactions taking place are complicated and in some cases unknown. During the smelting of iron it is customary to run off at regular intervals the slag which collects on the top of the molten iron in the furnace. At the Coltness works this slag is caught in a ladle, holding about eight tons, as it leaves the tapping hole. During the running of the iron any slag remaining in the furnace is led off from the "sow" and added to that already in the ladle. An overhead crane running on gantries past the furnace is then employed to carry the slag ladle to the "granulators" - see Figs. 4 and 5. The ladle is then deposited on an iron cradle mounted on journals about which it can be rotated by an electric motor directly geared to one of the trunnions. As the slag flows from the ladle it is caught by an open spout, which guides the stream on to a revolving drum running within a housing provided with a flue for carrying off the gases generated in the process. The drum is formed with open ends, and is perforated with numerous slot openings. Through each end of the drum a pipe is led into its interior, and as the slag falls on to the horizontal surface of the rotating drum, a jet of water containing five per cent. of magnesium sulphate in solution is sprayed into the drum, where it finds its way through the holes, and becomes intimately mixed with the slag. A third pipe at the same time delivers a jet of the same solution directly into the slag as it falls from the spout on to the drum. Partially as a result of the aqueous spray, and partly due to the impact with the revolving drum, the slag falls away from the granulator in a disintegrated condition. It is, however, still hot, and in a fairly coarse state (Note 8). The rate of tipping of the slag ladles and the speed of the drum can be varied as these are found to have at marked influence on the process of granulation.
The chemical changes taking place during this stage in the process are complex, and form an essential feature of the Colloseus method. What these changes are would appear to be for the present incapable of complete statement, but it is evident that they are chiefly concerned with the sulphur contained in the slag. Quantities of sulphur dioxide and hydrogen sulphide are given off, and the greater part of the calcium sulphide originally present is oxidised to the sulphate (Note 9).
In the event of any slight variation in the composition of the slag the strength of the spraying solution is altered, this apparently having compensatory effects. Although magnesium sulphate is employed in the spray, we understand that any salt of the earthy oxides which is soluble, in water can be used. These can again be replaced by the sulphate of calcium, aluminium, sodium or potassium, or mixtures of these with magnesium sulphate, while solutions of salts derived from the iron group - chromium, nickel, manganese, &c. are also available. The sulphate or chloride of iron is said to be especially favourable to the production of a cement which would resist the action of sea water effectually (Note 10).
As the clinker (Note 11) falls from the drums it is guided through shoots into buckets suspended from an overhead runway. The buckets when filled with clinker are elevated and attached to an aerial ropeway (Note 12) which conveys them to the clinker house, where they are automatically emptied, and the slag is stored until required for grinding. An end view of the "granulators" and the elevating gear of the ropeway is shown in Fig. 5. The circular brickwork tower to the right of the engraving contains a boiler for use in preparing the spray solution, which is stored in a steel tank on the top of the tower. Fig. 6 gives a view of the "granulator" from the rear, and in Fig. 7 a portion of the "Bleichert" aerial ropeway as it leads into the clinker storehouse is seen.
The succeeding processes in the manufacture of Colloseus cement are identical with those employed in the ordinary course. From the clinker house the granulated slag is transported by the buckets of an overhead runway to the first of the grinding mills. In succession the clinker is passed through as screw crusher, ball mills, and tube mills, the ordinary degree of fineness being such as to leave a 10 per cent. residue on a sieve having 32,400 meshes per square inch. After grinding is completed the cement is carried by a spiral conveyor and chain elevator to the hopper at the top of the building, being automatically weighed on its journey. The arrangements connected with the discharge of the hoppers are such as to allow a mixing in any proportions of the contents of two or more of them (Note 13). In Fig. 5 will be seen an exterior view of the mill-house, with the clinker store in the background. The small building between these is employed as a testing house, and here the cement is subjected to rigorous comparisons with ordinary material. Figs. 1 and 2 show views of the ball and tube mills, the photographs having been taken during the construction of the buildings.
The entire plant, granulators, conveyors, and mills, is electrically-driven, power being obtained from the blast furnace gases used in conjunction with a Cockerill gas engine, and from a large Rateau turbine running on the exhaust steam from several small Parson turbines, which are employed to drive the exhausters of the by-products recovery plant. Thus the entire industry, both as regards raw material and the power to work it, is based on the utilisation of "waste" products. We may add that this is a side of its business to which the Coltness Iron Company devotes considerable attention in several directions. As witnessing the extent to which it has adopted this process, it may be noted that at present there are nine furnaces connected with the granulators, each furnace producing 120 to 140 tons of cement per week, thus giving a total which will compare quite favourably with that obtained at most works devoted exclusively to the manufacture of cement (Note 14).
With regard to the strength of the material thus produced, we have been supplied with the following figures:
|lb per sq in||MPa (Note 15)|
|3 to 1 sand|
|compressive, 3 to 1|
A typical analysis of the cement is given below (Note 16):-
We are indebted to the Coltness Iron Company for permission to inspect the process at the Newmains works and for the photographs from which the engravings accompanying this article were produced. We also desire to thank the Collos Portland Cement Company (Note 17), Limited, 139, Cannon-street, London, E.C., for information supplied on behalf of Dr. H. Colloseus.