Ferro-Brickwork and Ferro-Concrete.

Progress, Volume IV, Issue 5, 1 March 1909, Page 175

Ferro-Brickwork and Ferro-Concrete.

(F. DE J. CLERE, P.R IBA)

The method of constructing Fa 10-B1 ickivoi ?. icalls, as shewn by thediagiam published lieiewith, consists nf bucks proportioned and shaped in such a manne) as to alloiv horizontal and vertical reivfoi cement loithout in any ivav breaking bond. This point hat ahtain been the difficulty, but it would appear now that it has been overcome in a •satisfactory mannet , and the method 7ws leceivecl the endorsement of many of the leading engineers in the Dominion For the last few years the whole of the building world, and indirectly a large poition of the public, have had their attention drawn to a comparatively new form of construction known as " f erro-concrete, " and ferro-concrete has been held up as the panacea for all the ills that building construction is heir to It is earthquake proof, it is rot proof, it is fireproof, it is light, it is cheap, and it will supersede brick and stone for walls, and will take the place of wooden or steel joists for floors. We are quite willing to grant that in ferro-concrete the world has gained a most valuable material, and that

work. Alas! What do we read now In a late Laxton, an absolutely unbiassed publication, it says: — "Some years ago concrete building received a great impetus, arising largely from the novelty of the idea. It has, however, long since subsided." The reasons for this are not far to seek. In all building a practical man allows that the making good of errors is a factor in expense. To rectify a mistake in concrete is most troublesome An opening may be set out only a few inches from the right place, but to correct this error a great deal of boxing may have to be pulled down and re-erected. In brickwork a mistake of this kind is generally made good in a very short time. Should the error be in ferroconcrete, it is appalling to think of the trouble that may be occasioned in order to set it right Then it is often said that in concrete work skilled labour is not required. There could be no greater fallacy. To begin with, the formation of the moulds requires the greatest caie and skill, and this has to be paid for, while the grading of the aggregates and the mixing and

equivalent to a mixture of three parts of clean sand to one part of Portland cement. It may be argued, with a show of fairness, that an aggregate consisting of hard stone, will produce stronger work than one of brick; but even here the assumption has been proved to be wrong, for the mere fact that the adhesion of the cement to the brick is better than it is to the stone more than compensates, when estimating strength, the difference in the hardness of the materials. This was shown by experiments by the English War Department in connection with a large building which they were going to construct. The tests were must carefully made, and the results show that a concrete consisting of six parts of broken bricks (rather soft kind and easily broken) to one part of sand and one part of cement at 31 days old, crushed under a pressure of 20 tons to the square foot, while the same matrix mixed with six parts of broken stone crushed with 14 tons 2 cwts. to the square foot. These weights, we might say, were the average weight, four examples of each kind being tested.* Now, it may safely be argued

the discovery, that steel will not rust when surrounded by cement, and that the adhesion of the two materials is so perfect, that they become as it were one is no doubt one of the greatest that has been made in the building world for very many years, second only, perhaps, to the invention of Portland cement itself. The possibilities ot the material aie wonderful; at the same time, concrete has, and always will have, great disadvantages in wall-construction as compared with brickwork, when the design is in any way intricate and the openings are many. In the late sixties and eaily seventies it was thought that* ordinary concrete would do wonders, and all kinds of apparatus for foiming the moulds were invented and used. In the Builder for April 13th, 1867, we read the following: — "Concrete constructions, it can be shown, are cheaper, healthier and safer, and therefore better than ordinary houses. The objection from a sanitary point of view to all the common brick, and lath and plaster constructions, is their absorbency of moisture, and in closely-crowded habitations their absorbency of miasma. Concrete is not by one quarter so absorbent of moisture and damp as brick, while it gives a washable interior surface. Its great economical quality is that it costs about one-half the price of brickwork. ' ' Could anything be more glowing or more conclusive of the triumph of concrete over brick-

depositing can only be done successfully by the most experienced men and these cannot always be found, and, when found, naturally requne more than the ordinary labourers' wages. How is joineiy fixed to coneiete? is a question often asked, more often asked than satisfactorily answered. Breeze blocks may be dropped into the moulds at approximately the right positions, but should they be overlooked, the trouble to get the necessary hold for the woodwork must be immense. Concrete building, too, is necessarily slow, time must be allowed for each filling to set before the next can be placed on it, for, unless the matrix has obtained some strength, the aggregate is simply a pile of loose stones that are constantly exerting a pressure outwards, and are not like biicks, that lie evenly on each other, and whose weight exercises a puiely vertical pressure. In concrete, too, as in a chain, the strength can only be estimated as being that of its weakest part, and one faulty mixing of the matrix ruins the whole. Of course, to a large extent this will apply to the mortar used in brickwork, but in* it we always have the strength which the ' ' bond or horizontal lapping of the parts gives, which is entirely wanting in concrete. With regard to strength. In making comparisons we have, of eouise, to assume that the matrix in the concrete and the mortar for the brickwork aie of the same strength, piobably

that if a concrete composed of broken bricks is of so great a strength, then surely the same materials laid in courses would be stronger, just as a coursed rubble wall is stronger than a random rubble wall. The question of shearing or sliding in the different courses may possibly occur. It can only be said that stones or bricks aie less likely to slide on each other when they are lying in horizontal beds than they would be when m oblique beds, for it must be borne in mind that many stones in concrete must be lying obliquely against those adjoining. With hoop iron bond, the shearing question might become important, but with wire bonding, and with frequent vertical rods and the joggled joints caused by the notches in the bricks in ferrobrickwork, it would not appear to be a factor for serious consideration. To the artistic mind, of course f erro-brickwork will appeal strongly. The abominations of stucco are so marked that any relief from it will be welcome, and in ferro-brickwork the actual material used can be left in its natural state, whereas in ferro-conerete it would appear that all "finish" must be in "compo. " The reinforcing of brickwork with hoopiron in the horizontal courses is a very old expedient, but in ferro-brickwork vertical rods are introduced, which, combined with horizontal metal, either rods or some sort of mesh that can be entangled in the mortar, will give a result which will make

the walls so strong that a building would be overthrown before being broken. Stone does not stand fire as well as brick; in the official reports made after the San Francisco earthsuake and fire ,the protection of all stone concrete by a facing of brickwork was strongly recommended. In connection with this matter, a series of tests made by Mr W. H. Biown, M.S.A., of York, England, are extremely interesting. Mr. Brown did not go further than to test the strength of brick beams when built in good cement mortar and strengthened by who netting in the horizontal courses instead of with

hoop steel. He made his beam eleven courses deep, nearly three feet, and ten feet long, in two thicknesses, one 41/4 in.,4 1 /4in., and the other 3in. (brick on edge) with a 4in. cavity between with wire mesh bonding in each horizontal joint This beam was found to carry a dead load distiibnted ovei the middle six feet of the wall, of 15,3001b5., or more than 6% tons. Mr. Brown does not tell us the thickness of the wire used in the netting, but it could not have been anything like as thick as No. 7 B W.Gr., and so it is fair to assume that with the use of the heavier wire, much higher lesults would have been obtained. To sum the matter up, the conclusions arrived at are briefly as follows: — A building, into the construction of which steel largely enteis, is very much better able to resist earthquake shocks and the lesults of settlement, owing to weak foundation, than one m wnicn tnere is little or no tensile strength in the different paits. That it is, however absolutely necessary that the steel should be protected from the action of climate or of fire. That the best results, when compared with cost, will probably be obtained by the steel acting in actual combination with its protecting material, the steel giving the tensile strength, and the other material the compressile. ■*That burnt clay products are better fire resisting materials than stone. That a material which "bonds" together is better than one which does not. That for wall or pier construction brickwork is better than concrete, provided that the "bond" can be retained and yet perfect adhesion to and protection for the steel can be obtained. That construction in ferro-brickwork would, under ordinary conditions, be lighter"* cheaper, quicker, more convenient, more fireproof, and more earthquake proof, will be capable of better architectural treatment, will be more easily altered, and will lend itself much more easily to the attachment of joinery than ferro-concrete. k See "Specification," No 9, page 69, paiag) aphs 8, 9, 10, also moe 153, paragraphs 6 and 7