THE TRUTH ABOUT FERROCONCRETS.

Auckland Star, Volume XXXIX, Issue 237, 3 October 1908, Page 7

THE TRUTH ABOUT FERROCONCRETS.

(To the Editor.) Sir, —Kindly allow mc sufficient space in your valuable columns to reply to Mr. Phi-cox's letter, wherein he states I gave the public a wrong impression, about concrete. No doubt Mr. Philcox has, like a number of others who doubt the stability of concrete, been led astray by external appearances. Some time ago I watched some of the Ferro Concrete Company's employees removing a quantity of concrete which had fallen on the decking of j the railway wharf from the pile makers 1 barrows, forming a coating about a couple of inches thick, and distributed over a fairly large portion of the -wharf. Although sharp bars and picks were used, it was a very difficult matter to get it off, and any inexperienced person would have taken it for the ordinary decking, which had been in for a few years before the concrete was spilt. Hundreds on the wharf must have witnessed, the same thing. As the result of long and continued experience in the construction of dbms, foundations and wharf work, I have no hesitation in saying that, contrary to what Mr. Philcox maintains, concrete will grip, and I might here add, if such Was not the case it would have become a. dead letter, as a building material, years ago, instead of coming more prominently into use every day, as it is. Wood, like the stone axe, has had its day, and as far as hnge constructions are concerned, we are largely entering into the cement age. Mr. Philcox need not be alarmedl about the rust on the exposed pile rods. Once embedded in a sufficient depth of cement no further oxidisation will take place. Although not strictly essential (rusty bars becoming quite bright after remaining in concrete for a length of time) all the steel is cleaned with wire brushes. Since my previous letter was published I have read Mr. Hamer's report of his investigations into ferro-concrete at Home, and was pleased to find he was of the same opinion as myself, that repairs could be carried out easily and effectively, which all goes to prove that Mr. Philcox has madle no case against ferro-concrete.—l am, etc., JOHN GUIN_VEN. ITo the Editor.) Sir, —Your readers are indebted to Mr Wm. Philcox for an excellent heading under which to provide some most useful and interesting information for your readers. "The truth about concrete" is just the very thing. The volume of work in concrete already carried out in Auckland, and likely to be engaged in during the next few years, and probably during the next century, warrants everyone in being interested, and in learning as much of the truth about it as possible. The opinion of Mr Wm. Philcox on matters pertaining to constructive works would be listened to with great respect, and carry much weight in this Dominion. By reason of that fact, one is naturally reluctant to express doubt as to whether or no Mr Philcox has set forth the whole truth as affecting the particular matter with which he deals. Without attempting to traverse the whole question of the fitness of reinforced concrete for wharf piles situated in seawater, or for decking, or buildings, or the like (and about which there is yet much of importance left unsaid), let us consider this question of the possibility of repairing defects in reinforced concrete. Probably it is not quite true to say that "a dab of cement will make it as good as ever," and it is not quite i true to say that, "in concrete work any defect can be easily repaired." But, a_s' a practical question, it would probably be not quite true to say that "it is I practically impossible to repair damage or to make good defects in reinforced concrete." It might be conceded that the highest results are to be attained when the work is scientifically and carefully performed in one, the first, undis- j turbed operation. It must be admitted that any measure of need for making good damage or defects is a cause for anxiety and regret to all concerned, because it is recognised, in all constructive work, that patching and repairs never can give results at all comparable to work uniformly and consistently well done as an integral part of the whole. And that is very true a_out concrete •work. But to_ err is human, and it is human, too, to fall short of perfection in anything, even in timber work, and in j brick and mortar. By the way, is not! mortar a kind of fine concrete ? We i want our wharves perfect, or nearly bo. The chemistry of the cement ] is perhaps not sufficiently considered or understood. Then there is tlie aggre-1 gate, the sand, the grading, the proportions, the amount of water, the kind of water, the mixing temperature, the wet- j ness, the dryness, the age, and the tex- ' hire, or the density of the work affected. I have seen concrete work scale off in j the way Mr Philcox mentioned. It is I generally believed that cement plaster cannot be made to adhere to concrete I surfaces, and that it is impracticable to properly unite old and new work. Mr Philcox mentions suction as the fac- j tor determining success. But is it the only factorY ls it quite impossible to unite old and new work, no matter what , precautions be taken? At what age does newer concrete refuse to be wedded I to older concrete? Has all the cement plaster come away from all the concrete I work in this.city, some of it having been executed quite a quarter of a century? If not, why has some of it remained I sound and good? Is any substance so dense that it has no porosity? Has steel any suction? Will cement adhere j to steel? If so, -why does it do so? Will cement adhere to rusted steel? Will it continue to adhere to steel that is j scaled -with rust? What would he the ! effect of loam in sand used in concrete? What would be the effect of mixing the concrete with saltwater instead of fresh water where that concrete is to surround steel reinforcement? What would be the effect of "* vibration upon new concrete? What should be done to prepare the surfaces of existing work to receive new work? Why does cement j stick to things at all? Those and other I questions intimately concern those engaged in concrete work, and have all to do with the "Truth About —I am, etc., JOHN MITCHELL