Page:The Building News and Engineering Journal, Volume 22, 1872.djvu/342

 322 THE BUILDING NEWS. Arprit 19, 1872. CONCRETE BUILDINGS. CORRESPONDENT of the English Mechanic having asked for some information on building with concrete, a practical farmer sends the following information in reply :— Close attention is required from the beginning to the end. Without close attention your correspon- dent had better use bricks and mortar. On the score of economy he must not be led away by the flaming accounts of the cement doctors. I have before me an account in which an equal number of yards of cement, sand, gravel, and broken stones are made to produce an equal number of yards in work. My experience has shown me that under no circumstances could I get more than 60ft. to G6ft. in the solid out of the 100ft. of material measured in—even in the case of walls. For roofing, which requires very hard beating, 7°28ft. of cement and gravel produced only 3-34ft. in the solid. A cubic foot of gravel and sand con- taining stones not larger than would pass through a 1fin. screen would weigh about 841b. or 851b.; a block of pure flint would weigh about double that percubic foot; the interstices must be filled partially or entirely with cement and sand, or air, or both. To make the calculation as to the comparative economy of concrete and brickwork—a rod of brick- work will take about 4,500 bricks, 26ft. of stone, or 36ft. of chalk, lime, and 70ft. to 75ft. of sand. Three hnndred and six feet of concrete, in pro- portions of one in ten—i.e., 9 parts gravel, 1 part eement—will require 410ft. of gravel and sand and A6ft. of cement. As to labour, I believe the usual calculation for ordinary brickwork in walls not less than 9in. thick per rod is 34 days of a bricklayer and labourer. In cement I have found that it takes six labourers, two stout lads, and a carpenter, to keep frames going to mix and fill about 240 cubic feet per day in walling. The labour bill for concrete is higher than that of brickwork. The economy will depend on cost of cement and aggregates. Mr. Tall puts his labour at 2s. per yard, and 6d. per yard for the carpenter ; in other words, one penny and three-twenty-sevenths of a penny per foot. From the above your correspondent can make his cal- culations as to cost. Quality of Cement.—Your Portland cement should weigh about 112]b. per bushel; the heavier the cement—proyided it is passed through not less than forty-gauge sieve, or 1,600 holes to the inch— the better. The heavier the cement the slower it sets, and the harder it is when set. Gravel—The real economy of concrete depends upon the quality and cost at which sand, gravel, and other aggregates can be produced. I have lately taken to washing my gravel—I only regret [ did not do it from the first; the slightest quantity of loam destroys the effect of a large quantity of cement. If neither gravel nor sand is procurable in the neigh- bourhood burnt clay ballast makes excellent concrete —in fact, better than sand and gravel. Mixing.—The cement, gravel, and sand should be turned over no less than five times—three times dry and twice wet. By turning over I do not mean simply chucking a shovelful from one side of the mixing board to the other, but turning clean over a half shovelful at a time, so that cement, sand, and Stones are all intimately mixed. Water.—The quantity of this depends much on the state of your gravel and sand. In no case should it be more moist than moist brown sugar; on this you will have a battle long and fierce with your workmen. Do not give in. The drier the concrete is put in the firmer it sets. Filling in Frames.—I again say put in as dry as you can, and ram as hard as you can, and do not fill oftener than twice a week or five times a fort- night. The fever speed of filling upon filling is utterly destructive of good work. One cement doctor recommends his framing as superior to that ofa rival by reason of his being able to fill twenty- four inches at a time as against that of his rival, who can only fill eighteen inches. Eschew as you would poison the filling your cement out of buckets. The use of buckets induces the workmen to mix the concrete with far too much water. Fill from the barrow in small shovelfuls, and let the shoveller take his time. This will secure more ramming from the man inside the frame. To the height of 20ft. run your cement on planks and stage; above that height set up a horse run. ——»—__ A new school for the parish of Buckhorn Weston, Dorset, to accommodate 100 children, was opened on Easter Monday. Messrs. Doddington & Farthing, of Mere, were the builders, the architect being Mr. Crickmay, of Weymouth. Civil Cugineering. —_>—_ THE INSTITUTION OF CIVIL ENGINEERS. T the meeting held on Tuesday, April 16, a de- scription was read of ‘‘ The New South Dock, in the Isle of Dogs, forming part of the West India Doeks,” by Mr. L, F. Vernon-Harcourt, M.A., M. Inst. C.E. The works referred toin this communication were constructed on the siteof the City Canal, the timber pond, and adjacent land. They comprised a dock of 264 acres, joined to a basin of 51 acres by a passage with reverse gates. The western entrance to the canal from the River Thames was retained, but at the eastern extremity a new entrance had been formed, leading from the basin to the river. On the south side of the dock, foundations for five warehouses had been prepared, and the superstruc- ture erected on three of them, with a quay shed in front. The main dock was 2,650ft. in length, 450ft. in breadth, and had quay walls all round it. The bottom of the dock, which was covered throughout with a layer of puddle, was 29ft. below Trinity high water, and the surface of the quay was 5ft. 10}in. above the same level. On the north side of the dock there were sixteen timber jetties, affording accommodation for 32 vessels, and opposite each jetty, in the line of the centre of the dock, were buoys for mooring the vessels. The dock walls were composed partly of brick- work and partly of concrete. Upon a concrete foundation, front, cross, and pack walls were built of brickwork, the intermediate pockets being filled with concrete. The back wall was only 14in. thick, its chief use having been to keep the concrete in place until it became consolidated. The walls were built up about 4ft. Gin. at a time, and the pockets were then filled with concrete, to the level of the walls, before another stage was commenced. The passage between the dock and the basin was 176ft. long and 55ft. wide; and having two pairs of re- verse gates, the level of the water either in the dock or in the basin could be raised or lowered indepen- dently of one another. This was important for the satisfactory working of the two entranees, as high water did not occur at both at the same time. The foundations of the walls and of the floor of the pas- sage consisted of concrete, the walls themselves being generally composed of solid brickwork, and the bottom of the passage being paved with ashlar ma- sonry. The heel-post stones, the hollow quoins* and the sills were of granite; while the remainder of the stone-work wasof Bramley Fall. The gates in the passage were of iron, with the exception of the -heel-posts, the meeting-posts, and the sill pieces, which were of greenheart timber. The gates were cellular, having two skins, formed of iron plates, separated by, and rivetted to, horizontal and vertical ribs. The skins were curved outwards, being arcs of circles whose radii were 60ft. and 120ft; but the sill-pieces were straight and met at an angle of 126° in the centre of the passage. Each gate was erected on the floor, only a few feet from its ultimate posi- tion, and was tested by being filled with water. After being moved into their places, sufficient water was introduced into the gates to counterbalance their tendency to float. The basin was 600ft. long and 370ft. wide, and was surrounded by a quay wall, precisely similar to the dock wall. The prin- cipal object of the basin was to serve as an immense lock during a rising tide; the water level being drawn down to that of the river when the tide had risen sufficiently, the gates were opened, and the vessels brought in, or vice versa, until high water, when the gates were closed and the vessels in the basin could be passed into the dock at leisure. By this arrangement the water in the main dock could be kept at a uniform level. The New East Entrance Lock, connecting the basin with the river, was 300ft. long between the gates, and 55ft. wide. The bottom consisted of a segmental brick invert, laid on a con- crete foundation, with springing stones of Bramley Fall; while the gate floors, and aprons outside the gates, were of ashlar masonry. Being constructed upon the site of the old lock, the north wall of that lock was allowed to remain, and a new wall, 9ft. thick, was builtin front ofit. The brickwork of the south wall of the old lock was so solid that blasting had to be resorted to for removing it. For the pur- pose of filling and emptying the lock, and also for lowering the level of the water in the basin, there were sluices in the walls of each side, at both pair of gates, in addition to sluices in the gates themselves. Beyond the entrance gates there were four outlets on each side, distributed along the walls so as to serve for clearing away any mud which accumulated on the apron. The portion of the Blackwall and Millwall Exten- sion Railway which passed through the land belong- ing to the West India Dock Company was carried out during the period of the execution of the other works. In this short distance, three swing bridges had to be constructed; two over the Blackwall Basin locks being for two lines of way ; one line being for the use of the East and West India Dock Company, and branching off to the north quay of the south dock; the other belonging to the Blackwall and Mill- wall Extension Railway, and going over the passage bridge, which was, therefore, only constructed for one line of way. The width of the Blackwall Basin locks was 43ft.; as, however, the line crossed the locks on the skew, the portions of the bridges span- ning the locks had to be made 66ft. Gin. and 80ft. in length respectively between the pivots and the ends, A new roadway swing bridge was also erected over the East Entrance lock. The whole of the swing bridges, gates, capstans, shuttles, and cranes were worked by hydraulic machinery. - The works were commenced in October, 1866. A cofferdam was made across the opening between the timber pond and the canal; the water was then drawn off from the timber pond, so that the founda- tions of the warehouses and the excavation for the new dock could be proceeded with before the water was excluded from the canal. In July, 1867, the foundations of the warehouses were completed, the tide was excluded from the canal, the greater part of the water in it was run off, and the foundations for the south wall of the dock were begun. In the fol- lowing month the cofferdam on the river side of the old East Entrance lock was set out. Considerable difficulty was experienced in driving the piles, owing to the bard nature of the ground a few feet below the surface, a stratum of natural concrete haying been probably formed by the mixture of gravel, sand, and shells, such as was met with in other places on the works, through which the sheeting piles, though fitted with heavy cast-iron shoes, were in most instances unable to penetrate. Soon after the dock walls had been commenced, the influx of water into the foundations was greatly inereased by the filling of the adjacent Millwall Dock, from which the water percolated through the adjacent gravel. To keep down the water it was necessary to employ three pumps, capable together of lifting about 10,000 gallons per minute, with, in addition, the oceasional use of a centrifugal pump capable of raising 1,500 gallons per minute. The dock and basin were care- fully puddled, to prevent leakage when they were filled with water. The foundations of the walls rested partly on gravel, and partly on stiff blue clay, mixed in some places with a good deal of sand. Along a portion of the site of the north wall of the dock there was such a firm and thick bed of conglo- merate that the concrete foundation was dispensed with, and the wall was commenced on the conglome- rate. The first stone of the passage was laid on the 4th April, 1868, when considerable progress had been made with the dock walls and excavations. In June, 1868, the cofferdam outside the east entrance lock having been completed, the water was removed from the second portion of the works, and from this period all the works were proceeded with simultane- ously. On the 5th of November, 1869, the dock walls and exca¥ations being completed, and the gates of the passage finished, water was let into the dock from the river; in December water was admitted into the basin and east entrance lock; in January, 1870, the new roadway bridge was ready for traffic ; and on the 5th of March in the same year the dock was formally opened. The dock wall, as constructed, had cost only £12 2s. per lineal foot, a result which was chiefly due to the largeemployment of concrete. The total outlay on the works had been £571,139—viz., for the dock, basin, passage, entrance lock, and ware- house foundations, £467,639; for the warehouses £60,000, for the railway £24,500, and for the hydraulic machinery £19,000. The designs for the several works had been fur- nished by, and the works were executed under the direction of, Mr. Hawkshaw, Past President Inst. C.E., the author being the resident engineer. Mr. Wythes, Assoc. Inst. C.E., was the contractor for the whole of the work, his representative being Mr. John Baldwin. The gates were sublet to Messrs. Easton, Amos, and Anderson, and the swing bridges to the Park Gate Iron Company, the latter being erected under the superintendence of Mr. Joseph Phillips, Assoc. Inst. C.E., while the hydraulic machinery was supplied by Sir W. Armstrong & Co. BRIDGE BUILDING IN ENGLAND AND AMERICA, Ar a recent meeting of the Massachusetts Society of Arts, the president, J. D. Runkle, in the chair, Mr. Edmund H. Hewins read a communi-