Re-Inforced Concrete

Progress, Volume XI, Issue 3, 1 November 1915, Page 474

Re-Inforced Concrete

The Kahn Trussed Concrete Steel System— A Chat with the N.Z. EngineerSome Educative Points.

When the Trussed Concrete Steel Company of London and Manchester determined to send out to New Zealand a highly skilled constructional engineer to forward its interests, valuable service was done to the prospective building-owners of the Dominion. Every kind of building material requires long study to get best results, and reinforced concrete certainly calls for skilled attention. Our architects and engineers are not behindhand in their knowledge of developments, but they will welcome the advice of a specialist such as . Mr. Arthur E. Evans, who is the engineering representative in New Zealand of the Trussed Concrete Steel Company for whom Messrs John Chambers and Son are New Zealand agents.

After a trip through the South Island, Mr. Evans has established his central office in Equitable Building, Lambton Quay, Wellington, where one can find a technical library most of us will envy. His first impressions of the country, from the view-point of a concrete expert, were worth having, and the “Progress” interviewer found that he believes a lot of educative work has to be done in the Dominion in connection with the use of reinforced concrete building material. “I was glad to come across so many Southern architects who were keen about the use of reinforced concrete” said the engineer. “They are looking for good opportunities of using it where its economy and efficiency can be well demonstrated. The building public require to be educated a good deal, however, in the use and advantages of concrete. ‘Progress,’ I note, has consistently reminded its readers of the advantages, and I would like to follow up the good work by stressing the need for paying more atten-

tion to scientific proportioning of the concrete mixture. It is thus possible to get higher stresses out of the material with very little increase in cost and superintendence. Our practice in England was never to do a job without ascertaining the percentage of voids in the material. If you get a stone or gravel aggregate, say threequarters down to a quarter, there is a certain percentage of voids which you fill up with sand. If you do not accurately ascertain the percentage, you either overload the mixture with sand, or you put in too little both courses tending to reduce the density and consequently the strength of the resulting concrete. Then, in turn, there are voids in the sand, which you fill with cement, an excess of which increases the strength but not in proportion to the increase in cost. The percentage of voids in the materal must be accurately determined if a proper mixture, strong and economical, is to be secured.

The prospects of concrete as a New Zealand building material? I can safely say ‘excellent’ to that question! Tiraaru I found to be an ideal district, and there is good shingle right through the Canterbury Plain. Steel in New Zealand costs more than in England, of course, and cementthough it is made here in an efficient way—bears a price which astonishes me, but in a heavy item like centering, the New Zealand constructor has an advantage in cheap timber for that class of work which to some extent sets off the disadvantages I have noted. Roughly speaking, reinforced concrete can be done about twenty per cent, cheaper in England than in New Zealand. Fortunately, from my viewpoint as a specialist in concrete, final materials are in a similar position, and 1 look forward with confidence to submitting estimates of construction on the Kahn system in competition with the ordinary materials.” Nowadays, when we are all so nervous about unfamiliar names, it is just as well to explain that the company which utilizes the Kahn system was incorporated in March, 1907, and its affairs are under the administration of a directorate consisting of Mr. Frank May (Chairman), Mr. M. Kahn (Managing Director), Mr. E. C. Hannen, and Mr. Benjamin Hannen. No German or Austrian capital whatever, and no person of German or Austrian nationality, is connected with or in any way interested in this Company. Twenty-seven “Kahn System” men are at the present time on active service with His Majesty’s Forces in the European War, one being a Captain in the Canadian Field Artillery, another a Lieutenant in the Canadian Engineers, and a third on the Staff while twenty-four are serving as non-commis-sioned officers and privates. One of the interesting things in Mr. Evans’ office, in addition to the library already mentioned with a feeling of envy, is a specimen of Roman concrete so hard that it will scratch glass. “Will our concrete of to-day ever reach that stage of perfection?” mused the “Progress” interviewer as he tried the glass-cutting experiment. “We won’t know until it has lasted as long as this bit of old Roman pavement” replied Mr. Evans. “A pity the Romans did not leave us some test sheets! ”