NEW PROCESS

New Zealand Herald, Volume LXXVI, Issue 23320, 13 April 1939, Page 8

NEW PROCESS

CONCRETE LAYING POST OFFICE BLOCK I preparing the material MIXED AWAY FROM JOB With the start yesterday of the pouring of concrete in the construction of a foundation raft which will carry the now four-storey block to enlarge the Chief Post Office, a new method by which concrete is mixed elsewhere and conveyed to_ the job, was introduced to Auckland. The system, which requires special mechanical mixing plant and conveyors, has been used in Wellington over the past three months and was operated in the construction there of the new Social Security building. The advantage of the new method is not only to ensure mixing of concrete on a more scientific basis than formerly, but it permits of a speeding up process. Three Shifts Being Worked Three shifts spread over the 24 hours of the day are engaged on the Chief Post Office addition. The start was made yesterday morning at 7 o'clock and 500 yards of concrete, representing the bottom slab of the raft, will have been laid to a depth of 12in. through the reinforcing steel by Friday. Actually the concrete could be mixed at a rate which would complete this (section of the foundation in 30 hours if it. were not that some slowing up of operations is necessary in stamping down the concrete through the steel. When the complete raft has been made, 1800 tons of concrete will have been used.

/ Method oi Mixing •7 "Under Public Works supervision the mixing of the concrete is done on the elevator system. From bins, at the touch of the operator, sand and shingle with the requisite amount of cement pour into a huge tank known as the "batcher," and from there pass down to the mixer. This sounds a simple affair, but actually the process is elaborate, everything being weighed according to the prescription in the operation. Even the water content is added according to prescription. An instrument in the process records the "wetness" of the concrete, registering on a revolving cylindrical graph a record of the particular batch, which also gives information of the particular time occupied in the mixing drum. - The concrete when mixed is poured into cylindrical tanks, each of which can contain three yards and is on a lorry. As the lorry mores to the job, the tank revolves by means of a special internal combustion engine, so that the mixing process is continued. Reduction of Noise At the Post Office job, men with deep concrete barrows on pneumatic tyres convey on the chain system the concrete from the lorry tank to the place where it is for the time being poured. As it is tipped from the barrows, several men in thigh boots spread it with shovels and stamp it well into the steel work under the supervision of a Public Works overseer. The floor of the raft, the Framework of which is a weaving of steel rods, extends over an area 78ft. by 172 ft. Not only is the method pursued an innovation for Auckland, an aspect welcomed in offices and shops adjoining is the absence of the jarring noise of concrete mixers, Indeed, from outside the temporary high fence surrounding the job there is nothing to indicate that within are gangs of men spreading concrete at a speed never before attained in construction in Auckland.