MODERN BUILDING.

Waipa Post, Volume XXI, Issue 1242, 13 May 1922, Page 4

MODERN BUILDING.

AMERICAN METHODS DESCRIBED. GET READY FIRST: WORK AFTERWARDS. A very interesting and instructive paper on modern concrete construction was read by Mr T. Mclnnes at last Tuesday’s meeting of the Te Awamutu Chamber of Commerce. The by the aid of diagrams on a blackboard, was able to clearly describe the methods employed in largescheme undertakings.

Addressing the meeting, Mr Mclnnes said that his paper was intended to give an idea of a carefully-designed plant for the handling of big jobs such as dam construction or any other big undertaking. They must admit that America was about the foremost country in the use of concrete, and she was spending £IOOO per year on research work and tests. Last year alone America laid 10,000,000 square yards of concrete roads, and she hoped to surpass that this year. In all she had 65,000,000 square yards of concrete roads laid in all parts of the United States.

Taking as an example a concrete dam and plant, which he sketched, Mr Mclnnes said that the plant was designed to handle 110,000 cubic yards of concrete and 150,000 square yards of excavations, the 'latter consisting of hard granite rock. The dam was to be 66 feet above-the present water level, and was being built with the coffer dam system, which allows the water to be turned, at will into any part of the river. The dam under notice was situated on the Hudson River, about five miles above Neyr York. It had a head race about threequarters of a mile long, having a power house at the bottom of the fall. The dam and head race gave an additional fall of 18 -feet. Its construction went to show what other countries vare doing in the development of power for cheap production. Stone for the concrete was quarried on the opposite side of the river, making the waste channel, and consisted of a hard granite rock, which was drilled 20 feet deep before blasting. The stone was then dumped into six-yard trucks with powerful steam shovels mounted on caterpillar traction, and taken across the river on top o.f the temporary dam to a site 300 yards up the river, where it was put through the crushers and screened. , It was then passed on to conveyer belts, and delivered to stone bins above the mixers or storage pile, which had a capacity of 25,000 cubic yards. The storage conveyer ended on a jib projecting 45 feet beyond the last trestle tower, and had its head pulley and motor 75 feet above the ground, giving command of every part of the storage bins. Pit-run sand was obtained from the canal excavations and carried by six-yard trucks to the top of the bins and mixer plant. The tsand bins fed the two mixers, the sand passing over a grizzly screen before Entering the mixers. There was a storage bin for sand which held 3000 cubic yards, and was operated by the same crane as the metal pile. America has been using the bulk system of handling cement for some time on. big jobs, and this has proved a great success in labour-saving. The cement is hauled to the site in special trucks having a double noof, with water-tight doors on top, for loading. The bottoms are caulked with a special fibre to ensure that no cement escapes during haulage. Each car carries l 3oo bushels of cement, equal to 16 tons, or 300 bags, as it is railed in this country. The cement car when it arrives is hauled on top of the storage bins, and run into a cement house, which is situated slightly in front of the stone and sand bins. The bins are lined on all sides With galvanised iron, which keeps out the damp and allows the cement to run freely. On one job eight bins are in use, which hold 250 bushels or bags, and terminate in a hopper gate at the bottom, through which the cement is drawn and conveyed by belts to smaller bins directly over the mixers. Two men are allowed 21 hours to dump and clean out a cement car, equalling 16 tons of cement, so there must be no “ go-slow ” policy employed there. The mixer plant is built round two proportioner panels, and consists of two stone bins, sand bin, and two cement hoppers properly elevated. The sand and stone bins are constructed with heavy framing and sheeted with Bx2 planking, all being double-braced to stand the enormous strain. Two one-yard mixers are in use at present, but provision is made for two more when the work is more advanced. At the present time the two machines are averaging from 70 to 75 yards per hour, which is less than two minutes per yard. Each shift of the boxing is so arranged that 300 yards can be dumped at one time, the boxing being held in position by powerful steel rods having sockets screwed on each end. Strong arms are then screwed into the sockets, which grip over steel rails, and vare easily removed When the next lift is required, and the heavy rods act as reinforcing through the dam.

The floating hatch hopper is suspended from the horizontal arms of two bell cranks mounted on a cam shaft. Attached to the end of the vertical bell crank arms are J-inch wire ropes, which by means of ballbearing pulleys pass under the end of a shaft on which three pans are suspended, and stone is drawn through the 18-inch gate by pulling a rope which raises and latches the gate when the weight of stone in the floating hopper balances the counterweights in the bottom pan, which then closes the stone gate. Pulling a second rope opens the cement gate, which adds to the stone balance and counterweight. Sand is drawn through the third gate, the total batch balancing ,the sum of the weights. This system of weight in the materials is very much used in big work, and gives a more even concrete than any other method of proportion and materials. There is even employed a batch counter, which is operated every time the ‘weights of material are made. The levers controlling the discharge from the batch hoppers are placed close to the three ropes operating the gates of the proportional panel, and the control of the mixer discharge is led up to the operating platform by a chain drive, so that the entire work

of charging, mixing, and discharging is done by a single operator. The concrete discharged from both mixers goes down to the foot of a steel tower 180 feet high; this tower ia equipped with sliding frames and boom plant having a fixed hopper at the top. The concrete is then hoisted to the top of the tower at a speed of 40 feet a minute, and delivered in chute® v to almost any part of the work up to 420 feet from the tower. One would imagine that the. size of the stones would make no difference in chuting the mixed concrete, but it is found that the stone passing a 3-inch mesh did not flow so evenly as a 2|-inch mesh. Difficulty was also found in fixing the right slope of the chute; hence the height of the delivery tower, the best results being a 21 to 1 grade. The Americans are very particular concerning grading of material on big works, as they put that down to be the difference between good and bad concrete. This caused very frequent sieve analysis to be made both of the crusher-run product and the pit-run sand, which varied considerably. .Summarising Ms remarks, Mr Mclnnes concluded that the Americans were proving that money well spent on plant lay-out, and by situating th© , machinery in the proper place, would save thousands of pounds in every undertaking of size. Every little detail had to be considered; the plant was useless unless set up in the right place. Compared with old methods of handling concrete —which in pre-war days was worth from 12s 6d to 15s per cubic yard for ordinary foundation mixing and dumping—it was not difficult to see the immense saving through, modern methods.

Mr Hopper thanked the speaker for Ms paper, but suggested whether, in the present time of distress and unemployment, it was best, economically, for the country to spend, money in labour-saving devices or to absorb its available labour. ( Mr McCarter, moving a formal vote of thanks, said the system was applicable in New Zealand now or at any time. From a national point of view public works had to be done as cheaply as possible. It was folly to suggest ; piling up debt for the future in order to tide over a period of unemployment.

Mr Taylor concurred. He appreciated the practical suggestions contained in the paper just read. Mr McCarroll said the principles of a tower to distribute the concrete had been introdugted in Auckland three and a half years ago. At first some of the difficulties enumerated were experienced. The vote of thanks was carried with acclamation.

Mr Mclnnes, in acknowledgment, said that if New Zealand could not give its unemployed a better job than shovelling concrete it was a bad look out. There were other works programmes which could prove more profitable.