ASH AND CLINKER BRICKS.

Press, Volume LX, Issue 18151, 14 August 1924, Page 4

ASH AND CLINKER BRICKS.

; METHOD OF MANLTACTUIIE. ]n view of the long continued scandal of the scarcity and high prices of bricks which we are now actually compelVd to import from the Continent, fn London as well as in Devonshire, the building industries should agitate for the adoption of modern scientific methods in the manufacture of bncks, savs a.writer in the London '■lllustrated Carpenter and Builder." For example we aro throwing away every ?,S millions of tons of ash and chuteer blast furnace slag, and similar material, all of which is waiting to be conve ted into high-grade bricks. In the case of steam .boiler ashes ph-ie the annual output m Great Britain i's over 12,000,000 tons per annum, and tier* is also a vafit amount from destructors,, household firos. and general furnaces of every description, lite process of brick-making on these lines consists essentially in roughly gnndi„r tho ash and clinker equal to all through an 8-mesh screen (eight holes per linear inch) and then adding about (j-10 per cent, of its weight of good quality lime that has been ground to a fineness equivalent to all through a oOinesh screen (fifty holes per linear inch). To this mixture is now introduced about 10-15 per cent, of water, unci the whole is then heated almost to boiling bv steam, whilst being continuallv agitated in a patent mixer. Tho hot thick mass is then discharged into a storage tank or silo, whero it is allowed to He for 12-3G hours, so as to ensure that absolutely no trace of unslaked lime remains. It has been shown by a British firm who have long been specialists on tho design and construction of plant for lime-sand, ash, clinker, and blast furnace slag bricks and were one of the pioneers of this process, that tho elimination of the minutest quantity of quicklime, such as is present in lime slaked by an ordinary method, is tho whole secret of the process.

finishing Process. After tho mixture has matured in tho silo a further small amount of water is added, if necessary, to bring it to the right consistency, following which it passes through a brick press operating at two tons pressure per square inch. Tho brick shapes are subsequently stacked on a small waggon holding 400 bricks and wheeled into a long brick or concrete tunnel, in which tlicv are subjected for" 5-6 hours to steam at atmospheric x>ressure —that is, about 212deg. Y. By this means the free silica (Si 02), always present in tho a.sh and clinker, combines with the lime to gLve calcium silicates, which act as a binding material for the whole mass, forming an intensely hard and homogeneous brick. The bricks, on being withdrawn from the steam heater, are ready for use almost immediately, and the whole process is extremely simple and can ba worked with unskilled labour. As- already indicated, the bricks are of the highest grade, being of a slaty bluish colour, very like Staffordshire blue brick, and thev possess an excellent compressive strength, superior to -ordinary burnt bricks, the average crushing strain being, say, 55001b. per sauare inch (355 tons per square foot), slight cracking taking place at 42001b. (270 tons per square foot), and general cracking at 54401b (350 tons per equaro foot). Also <"iey possess low absorption qualities for water and are eq.ua.llv porous to air. Thoir excellent qualities are well known on the Continent, where they have been used in millions for years past. Another great advantage of these bricks is that each one is a "facing" brick, being mathematicallv straight and of uniform size, witu no sign of warping, twisting, and irregular expansion. In this connexion the British Standards Specification can l>e consulted with regard to the tests for sand-lime and the, analogous clinkcr-liine bricks. Finally, the comparatively small steam user can nso this process to advantage, since, if time is of no consideration, tho bricks will harden without steaming if simply allowed to Tie about in the open air for two or three months. All that is required, in fact, for a good grade of brick is an ordinary common mortar mill and an edge runner mill, together with a brick moulding machine, tho total capital cost being most moderate. Obviously, therefore, the whole question is of national importance in more ways than one, and there is no reason v,-hy large building firms should not in this way manufacture a large proportion of their own brick requirements.