A NEW INDUSTRY FOR SCOTLAND.
Portland cement (so called owing to its colour resembling Portland stone) is imported into Scotland by thousands of tons a week (Note 1), and its use is so common and so extensive that it needs no description in a country whose engineers have largely pioneered its use for docks and harbours, and whence comes the famous "granolithic" pavements.
Its chief source of supply for long was the Thames and Medway, but of late years considerable quantities have been imported from the Continent. Probably owing to hard times in the home market foreign makers have been driven to find an outlet here. The Germans and Danes send Portland cement here, and the market is flooded with cheap Belgian cement, called here Portland, but in Belgium known by its proper name of "natural" cement, it being a material burned in the same way as lime, and left to "slake" before grinding, in much the same way as Lias lime is made in England. Real Portland cement is a carefully prepared combination of carbonate of lime and silicate of alumina made to a definite formula with a definite chemical composition. The carbonate of lime may be chalk or limestone, and the silicate of alumina alluvial clay or shale; it matters not, as in all cases these raw materials are ground to the same unpalpable (sic) fineness before admixture. While in the South of England chalk is used, in the Midlands Lias limestone is the principal raw material, and probably of the cement made throughout the world two-thirds has limestone as the basis.
It is only in recent times that attention has been drawn to Scotland as possessing proper raw materials for the manufacture of Portland cement and a careful search located these in the Lothians. The Cousland Limestone Quarries, near Dalkeith, were thoroughly and scientifically tested and found to contain exceptionally suitable materials in abundance for Portland cement making.
The limestone there has the following composition (Note 2):—
|Carbonate of lime||94.77|
|Combined water and loss||1.02|
And the shale found in the same quarry:—
|Carb. of lime||7.80|
|Combined water and loss||12.71|
These raw materials compare favourably with the best to be found on the Thames and Medway or elsewhere.
Having proved the suitability of the raw materials, the Caledonian Portland Cement Company (Limited), with office at 39 Dock Street, Dundee (Note 3), was formed, with a Board consisting of Scottish gentlemen, associated with, as technical director, Mr J. L. Spoor (Note 4), of Rochester, Kent, who has behind him twenty years of practical Portland cement making experience.
A short description of the plant and process may be of interest.
The extensive quarries are situated on the ridge and adjoining Cousland village, and at the foot of the hill the cement works have been erected. A tramway connects the quarry with the works, and a siding from the Ormiston branch of the North British Railway gives ready access to the railway system. The limestone is run down from the quarries to the crushing plant, where it is reduced to the size of road metal, thence, by gravity, falling into further pulverising machinery, which reduces it to fine powder. This powder is conveyed automatically into storage bins. The shale undergoes a similar process, and is also binned (Note 5). From these separate stores the raw materials are carried by conveyors and elevators to an automatic weighing machine, which is so set as to weigh at one operation the exact quantities of each material required for the proper mixture (Note 6). This object having been obtained, the mixture finds its way into the huge cylindrical tube mill, where it is thoroughly incorporated and ground to the finest powder, thence passing on to the brick presses to be made into bricks. Up to the delivery of the bricks from the presses, the whole process is automatic and free from the variations usually found in cement works built on haphazard rule of thumb lines. A constant scientific check on the mixture is kept by analysis throughout the day, with the object of securing regularity of quality and uniformity of product.
The bricks are then placed in the hoists and taken up to the top of the kilns, in which they are burned to clinker.
This clinker, after passing through Blake crushers, is reduced in ball mills and finished to fine powder in tube mills, passing by automatic conveyers to the warehouse floors as the finished Portland cement for the market. It will be seen that the plant is what is termed a "dry process" plant, and designed to eliminate rule of thumb risks by automatically controlling the manufacture on scientific lines.
The most modern plant by the best makers has been installed. The engine (compound condensing, with rope driving), of over 400 h.p., is by Shanks (Note 7), of Arbroath. The boilers are Scottish, while the Continent has been laid under contribution for the ball mills and tube mills. Leeds has furnished the brick presses (Note 8), Leicester the crushers, while locally everything has been ordered that could be suitably obtained. The kilns are the well-known Schneider kilns. The whole plant has been erected under expert supervision, and by local workmen, who now, under the experienced cement works manager, Mr Greaves, manufacture the cement. The company has built cottages for the work people in the village of Cousland.
The warehouse is alongside the railway siding and trucks are loaded under cover.
The testing laboratory is fitted with the requisite chemical and mechanical appliances for thoroughly testing the cement and controlling its manufacture.
The manufacture has been carried on all this summer (Note 9), and the cement has been put to the proof of actual use in all classes of work by builders and contractors, and has given great satisfaction.
The best authorities have also made independent tests with satisfactory results. On the side of chemical composition, Mr G. H. Gemmell, F.I.C., of Edinburgh, found it to contain (Note 10):—
|Water at 212°F||0.20|
|Combined water and loss||1.10|
|Oxides of iron and alumina||9.70|
And certifies it to be a Portland cement in which the ingredients are in correctly balanced proportions, free from adulterant (Note 11) of any kind, and closely corresponding to cement made from Thames chalk and estuary clay, or London Portland cement.
Professor Stanfield, of the Heriot-Watt College, certifies the cement as tested by him as of first-class quality, tests of 440 lb. at 7 days, and 622 at 28 days, while a cube of concrete made of two parts cement and three parts granite chips gave a compressive test of 4218 lb. per square inch.
Tests made at Leith Town Hall recently gave at 7 days, 516 psi: at 14 days, 546 psi and at 28 days, 666 psi.
Tests made by Mr Blount, F.I.C., of Westminster, W.S., gave at 7 days, 623 psi and at 28 days, 743 psi.
While in all cases the fineness of grinding is excellent.
The Caledonian Portland Cement Company (Limited) have set themselves the task of supplying their home market with a safe, sound, un-adulterated article at a competitive price. It will be seen from the above tests that they have succeeded, and are producing a genuine Portland cement of the highest order. They are avoiding the "quick-setting" class of cement, which attain high tests at short dates and afterwards decrease and fail; rather they produce the slower setting, reliable cement, which goes on increasing in strength with age.