Page:The Building News and Engineering Journal, Volume 22, 1872.djvu/541

 JUNE 28, 1872. THE BUILDING NEWS. 519 to ascertain the effects of lead placed, as was fre- quently done, between the joints of cut stone columns, &c., with the object of distributing the stress uniformly over the beds of the stone. The experiments were made upon circular blocks of Bath stone (Box Ground and bottom bed Corsham Down), 3ft. long by 10}in. and 15in. diameter, or one set twice the area of the other, the lead being cut 2in. less in diameter than the beds of the stones themselves. “The results pointed to the conclusion that lead so placed between the beds of the stones reduced the bearing strength of a column to con- siderably iess than that of a column of only half its sectional areain which the stones were completely bedded. On examining the sheets of lead used in ‘the joints, they seemed to have been under compression at avery few points only, and not to have in any way tended to equalise the pressure over the area of the joints. These experiments also seemed to indicate that raking out the joints of cut stonework, to save ‘the arrises in case of any compression of the joints, when bedded in mortar, should not be carried too far. Such questions were, at any rate, worth ‘investigation. In allexperiments upon stone it was essential to know the exact description of the stone, the quarry it came from, and, if possible, the parti- cular bed in the quarry. The time the specimen ‘had been quarried should be stated, as some stones when green would stand very little stress, but hardened considerably, in a longer or shorter time, when exposed to the air. If the specific gravity, or weight per cubic foot, of the specimen were given, it would afford some clue to the state of the specimens experimented on. CONCRETE. Before leaving the subject of stone, the author referred to what he regarded as an artificial stone, widely used in the present day, viz., concrete. He thought his hearers would agree with him that a series of carefully-made experiments on the strength of different kinds of concrete would be of great value, under varying conditions, as to the nature of the lime and cement used, the description of ballast, proportion of large and small stuff, and mode of mixing. With good Portland cement, well-burnt and well-ground, he should use with confidence for ordinary foundations 12 of ballast to 1 of cement, provided he was sure of its being properly mixed; but with ordinary workmen, not properly drilled in mixing the materials, 10 to 1 would probably be more advisable. It would be well to know how much the strength of concrete was affected by the different modes of mixing in vogue. For his own part, he should insist upon the mixing being performed as follows:—A yard measure to be half filled with ballast, then the measure of cement to be added, and the yard measure filled up to the top with ballast. On removing the measure, the ingredients get partly mixed, and the cement did not get blown about so much as when placed at the top of the heap; it should then be turned over twice ‘dry, and shovelled into a third heap, each shovelful being sprinkled from the fine rose of a watering-can as it was thrown on the heap, whence it may then be removed to the trenches. Captain Seddon here exhibited a block of concrete which had been broken witha pick out of a newly-built dock wall, in which 12 to 1 Portland cement concrete, mixed in ‘the manner described, was employed, and he thought it was strong enough for any foundations. In making experiments the mixing should be done in ‘bulk, at least half a yard cube being mixed at a time, and not in small quantities, which were more carefully prepared than would be the case in prac- tice, and the blocks should be at least 12in. cube. MORTARS. Passing from concrete to mortars, the results of some experiments made for the Patent Selenitic Mortar Company showed that in mortar made with common stone lime—Burham or gray chalk lime, similar to Dorking lime, was used—3 of sand made a stronger mortar than only 2 of sand, and stronger again than 4 of sand, which was probably due to 3 to 1 being about the point at which more sand would weaken the cohesive and and adhesive properties of the mortar to a greater extent than its setting or hardening would be pro- moted by increasing its porosity. With selenitic mortar, 5 of sand was the best mixture to resist thrust; then 4, then 6 of sand; but for adhesion and to resist tensile stress, 4, and then 6, and then 5 of sand. From which it was to be gathered that 3 to 1 was the best proportion of sand to stone lime in common mortar, and 6 to 1 in selenitic mortar, since the latter gave a mortar possessing double the strength of common stone lime mortar. However, in using the selenitic mortar at Chatham lately, 6 to 1 was not found to 1, which was being now used. Although the 6 to 1 mortar set very hard, it was so ‘* short” that it took longer to work, the loss of time out- weighing the saving of sand. The proportions now being used were 4 to 1 for exterior work, and 5 to 1 in the body of the walls. Mr. Street had, the author believed, had some further experi- ments made with the selenitic mortar in connection with the new Law Courts. THE BEST MEANS OF ADDING TO OUR KNOWLEDGE OF BUILDING MATERIALS, In concluding his paper, Captain Seddon proceeded to consider the best means of adding to our know- ledge of building materials, and the placing of such knowledge on a firm and unassailable basis. He said: I think it will be admitted that, in a matter so important to all as the possession of accurate information with regard to the strength and pro- perties of building materials, all who have it in their power should do their utmost to further the carrying out of a carefully conducted series of experiments on an exhaustive scale, in order, if possible, once and for ever to clear away all doubts and doubtful theories. It was because I felt that the members of this Institute were, above all others, most deeply interested in the prosecution of such experiments, because I knew how much depended on their united action in this matter, and that, were they each and all to assist, the whole question would soon be put upon avery different footing, that I undertook to read this paper here to-night. Means for carrying out a complete series of experiments are placed within our reach, and of a description which I firmly believe leaves nothing to be desired. Having often had occasion to visit Mr. Kirkaldy’s testing works at Southwark, I have been struck with the immense advantage which a public—I might almost say a national—testing apparatus, open to all, such as he has provided, has over all private efforts, however numerous. I am perfectly aware that attempts have been made to detract from the merits of the machine designed and erected by Mr. Kirkaldy. Prejudice and self-interest are always to be found arrayed against anything new, however successful it may be, in addition to which a certain amount of opposi- tion is always to be expected from the machine refusing to give results consistent with the theories or interests of those who are consulting the oracle. Different experimenters with different objects in view, different modes of conducting and recording the experiments, different kinds of apparatus em- ployed, often unscientifically constructed and erring in opposite directions, must, perforce, give different results, especially when recorded facts are read by the light of preconceived theories. On the other hand, we have a single observer of facts, with a life-long training to the work, systematically re- cording the results given by a machine of most perfect construction, capable of testing materials in large masses, far beyond anything previously at- tempted. Such an experimenter, who has made it the study of his life, is far more capable of recording and comparing facts with accuracy than one who has had no previous experience at such work, A comparison of the results obtained by different ex- perimenters with the same machine, even, is generally a hopeless task, from the absence of any uniform system of recording facts or conditions, such as the temperature, dryness, or exact nature of the speci- men; if wood, from what part of the tree, and where grown; if iron, the alteration in form, &c.; if stone, the quarry, part of quarry, time since quarrying, Ge. I look upon Mr. Kirkaldy, silently but powerfully working day by day ina special field of knowledge, collecting and comparing facts, as one of the great levers always at work to assist the progress of scientific knowledge. It is by men like him that the world at large is constantly being benefited, though too often without acknowledging their benefactors; by men who, perceiving a great want, and the means of supplying it, devote the whole of their energies to proving the truth of the ideas they are impressed with, and persevere in working them out to a successful issue. If all the members of this Institute, especially those who have large works on hand, were to cause but a few ex- periments to be made, in a short time numberless facts would be collected and compared. and the range of our knowledge of building materials would be rapidly extended. The question naturally arises, who is to pay for the experiments suggested—the builder, the archi- tect, or his client? The answer is, neither of the three, but the manufacturer or producer of the material. For instance, let us take stone. On any large work being projected, stone-merchants and quarry-owners, without number, press the rival claims of their different stones upon the architect. to give such good practical results as 4 and 5 | Well, let all who wish to supply the material for the work send in specimens to Mr. Kirkaldy’s works, say three 6in. cubes, three blocks 6in. by 6in. by 12in., and three 6in. by 6in. by 18in. Here you have the material at once to make experiments on, the cost of which would be defrayed by the success- ful competitor. Of course, in the case of stone, the selection would not depend solely upon the results of experiments on the strength of the material, since its weathering properties, &c., would have also to be considered. It may be said that only well-seasoned and prepared blocks would be submitted. This could either be met by the architect employing some one at the quarry to select the stones out of which to cut the specimens, or by seeing that the stone supplied come up to the standard of the specimens submitted for testing. Such a system as this could be applied to all classes of materials, and the cost of the experiments would fall on the proper shoulders. It might possibly be as wellif a com- mittee of this Institute were to lay down, in con- sultation with Mr. Kirkaldy, the information which ought, in each kind of material, to be recorded; and if they were, as far as possible, to circulate amongst the members instructions with regard to the number and sizes most desirable for the specimens of various kinds of materials to be experimented upon. If some such course as that suggested were acted upon by all the members of this Institute, and by the Civil Engineers as well, before long a vast number of experiments would place all disputed points beyond the regions of doubt and uncertainty; we should hear of fewer failures, and avoid endless little troubles which are never heard of as failures, though in strictness they should be so classed, just as much as those which lead to serious results. In conclusion, I can only say that if seeing assists believing, any gentlemen who take an interest in the subject I have been dealing with this evening, and who have not seen Mr. Kirkaldy’s testing appa- ratus, would, I am sure, be amply repaid by a morn- ing or afternoon spent in watching it doing its work ; and I feel convinced that they will come away, unless they have a rival machine of their own, satisfied that it is capable of supplying with accuracy all the information they are likely to ask for. As I have already stated, one of the most important points tomy mind is, as it were, the public character of the works, open to all comers and all materials, and containing complete and accurate records of experiments made with no aim or object but of truthfully recording facts. I think that such an institution ought hardly to be left to the unaided enterprise of a single individual. I look upon its success as a matter of national importance, greatly affecting the safety as well as the pockets of the public at large, whether sitting in their houses, whirling along on railroads, or crossing the seas in ships. Numberless lives are year after year lost, lifelong miseries caused, and thousands upon thousands of pounds wasted, from a want of proper knowledge of the strength and properties of building materials. DISCUSSION. The discussion upon the paper took place at the meeting of the Institute on the 27th ult., the Pre- sident, Mr. T. H. Wyatt, in the chair. With refer- ence to selenitic mortar, Major-General Scorr said that in dealing with limes and cements he had found by experiment in the case of pure limes that they were not dealing with a material like hydraulic limes. The setting properties of pure limes were due to the action of the carbonic acid gas, but in hydraulic limes the converse of this was true. While the pure limes owed their setting properties to the action of the atmosphere, the hydraulic limes owed theirs to the action of the water. Between these extremes all varieties of lime were found, owing their setting partly to the atmosphere and partly to the water.—The Prestpenr said that he had wished to try the selenitic process in connection with concrete, but the builder had objected that concrete so made would not set in the bottom of the trench.—Major-General Scorr said that what the builder might have regarded as “setting” was really only the first slaking and warming of the lime. If it had been examined after a month or so, the re- sult would have been astonishing.—Professor Kerr referred to a plan he had seen adopted, viz., the mixing of lime and ground chalk in certain propor- tions, and then adding a very large proportion of sand—he thought four or five times the quantity of the lime and chalk combined. It was considered that the carbonic acid gas was communicated from the chalk to the mortar, the induration and setting being very quick. He had seen mortar produced in this way which was equal in strength and appear- ance to Portland stone.—Captain Srppon said, with reference to selenitic mortar, he had found in works at Chatham that notwithstanding the large admix- ture of 6 parts sand to 1 of lime, the results