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PRODUCTION OF RAPID HARDENING CEMENT IN HONG KONG
The recent announcement by the Green Island Cement Company that they are now producing Rapid Hardening cement made an excuse to visit their plant recently. It was a pleasure to visit this plant as it is refreshing to see modern methods of manufacture and handling when so much in Hong Kong is done by mediaeval methods. From beginning to end in the Green Island Co's works everything is either handled by gravity feed or mechanically by elevator or conveyor belt.
The first place to be visited was the laboratory where Mr. T. A. Williams, B.Sc., A.R.I.C., the Company's chemist, with his staff, is continually taking tests of the raw materials as they arrive and again as they are introduced into the manufacturing process as well as tests on test cubes made by the Company and cubes brought in for test from outside.
There are two compression testing machines, one Macklow Smith vibrating machine and three George Salter type Tensile Test machines. One of these latter, incidentally, having been made by the Japanese during their war time occupation of the plant. It is a trifle crude and heavy but seems to be quite efficient.
We saw in the laboratory some samples of lightweight concrete of different specific gravities, one of the samples be- ing light enough to float in water. There would seem to be possibilities for the manufacture of this product in Hong Kong, although it was tried quite recently here and the firm manufacturing it were not successful in producing a stable product.
The chemistry of cement manufacture is interesting in that fresh sets of conditions are continually being presented by users of cement and it is the chemists' job to design a cement that will fulfil the required conditions. At the moment the Green Island Company is working on a cement for oil wells. The concrete is pumped down the oil well to form the casing. It must have a high ultimate strength but a very slow setting time. Gypsum is necessary to slow up the setting time but reduces the strength. A fine grind gives higher strengths but speeds up the setting time. In rapid hardening cement the fine grind gives the high ultimate strength and gypsum is added to slow up the setting time. The loss of strength due to the higher proportion of gypsum is more than offset by the increase in strength due to the fine grind,
In oil-well cement, to comply with the conditions for slow set and high strength under high temperatures, there must be a balance between fineness of grind, gypsum content and limestone content.
A high iron content, Mr. Williams tells us, makes a dark coloured cement and this cement is more resistant to the action of sea water than a light coloured cement. The Green Island cement now being manufactured has this high iron content and should therefore be good for marine work.
We believe that shortly there will be in Hong Kong a great deal more gypsum plaster used where a high class finish is desired and it is therefore worth while running over the rules to follow where gypsum comes in contact with cement and cement paints.
1.
2.
Gypsum on green cement. May give trouble as the cement in contact with the gypsum will deteriorate and thus cause loss of key and flaking.
Cement paint on gypsum plaster. The cement in the paint will deteriorate under the action of the gypsum and prevent the setting of the cement and will also cause flaking.
3. Gypsum plaster can be applied to concrete walls or brick and cement mortar provided the wall is first sealed with a bituminous emulsion sealing coat.
It is interesting to note that practically the whole of the raw materials used by this company has to be imported. The limestone used comes from Canton and Haiphong, the coal from Japan and South Africa, the iron ore from a mine in the New Territories and the rock gypsum from the U.S. Gypsum can be obtained from China but is too expensive. Clay is dredged from the bay off the Company's wharf and provides silica, alumina and a little iron. To balance the high silica content and make the mix more fusible more iron must be added in the form of iron ore. The S. African anthracite and the Japanese coal are mixed in the proportions of one to three. It is not only the chemical analysis but the price that controls this ratio,
The
materials all arrive by sea. raw
An overhead ropeway carrying grab buckets carries the limestone to the storage area where it is dumped in piles according to its source of origin. The same ropeway carries the coal to its covered storage where it, also, is stored according to its source of origin. The clay is either stored or carried direct to the wash-mills where it is washed, mixed with water and kept in suspension by compressed air agitation.
The limestone is picked up by a steam driven grab crane, dumped into five ton side-tipping steel wagons and hauled by steam locomotive to the crusher shed where the stone is tipped into the hoppers feeding the crushers. These jaw-crushers break the rock down to 21" and under. The crushed rock is
then carried by belt conveyor to roll crushers which reduce it to " and under. A further conveyor belt carries it to the concrete hoppers feeding the tube mill.
Coal is carried from the storage through weighing devices by elevator and conveyor to the coal grinding mill located adjacent to the firing end of the kiln. The coal is here gound to powder in a ball mill ready for injection into the kiln.
The mixed ingredients of limestone, clay and iron ore în the form of a slurry are fed into the opposite end of this kiln and travel by gravity to the firing end. By the time the material reaches this end of the kiln it is in clinker form and is tipped out and delivered to the clinker store.
The kiln, which is the most imposing part of all the plant, is a tube 254 feet long and varying in diameter from 7′ 9′′ to 11'. The kiln is rotated by a 60 B.H.P. electric motor through reduction gearing and is carried on five steel tyres. These tyres are supported on cast steel rollers turning in water- cooled bearings. A new kiln is on its way out from U.K, and should be installed and working next year.
After the grinding process in tube mills the cement is stored in concrete silos from where it is delivered by gravity and worm conveyor to the bagging plant which tills and weighs bags automatically. Sampling doors provided in each silo and, if a customer so desires, samples can be taken from seven different levels and the silo sealed and reserved for that particular customer.
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In spite of the considerable damage done to the works by our own sabotage in 1941, by Japanese neglect and by two direct hits by American bombs the plant was started up early in 1946 and was producing cement in February of that year.
Those of us who know the difficulties of supply, the lack of skilled labour and the necessity of improvisation in those days feel that Mr. J. J. Cameron, the Works Manager, who was responsible for this rehabilitation, deserves congratulations on a very fine achievement.
THE BANK OF CHINA, HONG KONG
Work was started on the site of this building in the middle of March by the firm of George Wimpey and Co. Ltd. The only work being done at present is soil analysis from samples brought up from borings at various depths. According to the results of these analyses in the London laboratory of Wimpey so will the foundations be designed. Only then will the real construction work be started.
We are unable to publish any drawings or plans at the moment but, since this is probably the finest building site in Victoria, we feel confident that Palmer and Turner, the architects, and George Wimpey will respectively design and execute a fine building worthy of the site.