The Barber-Greene Mixing Plant
A—Aggregate Supply
B-Cold Elevator Feeder
C-Cold Elevator
D-Bulkhead
E-Adjustable Gate
F-Drum Feeder
G-Drum
H-Dust Collector
J-Hot Elevator
K-Combustion Chamber
I-Burner
M-Bitumen Tank
N-Heating Flues
O-Metering Pump
P-Apron Feeder
Q-Hopper
R-Calibrated Gate
S-Spray Chamber
T-Fines Feeder
U-Pug Mill
V-Side Discharge Conveyor.
GAMMON
Control and checking of the bitumen content was done in a site Laboratory by means of a Hot Extractor and not less than two samples per day were so tested.
Density tests were also made on cut-outs from the finished work and results of these were particularly good and consistent throughout the working period.
In the case of the Wearing Carpet an average density of 120 lbs, per cubic foot was reached and sometimes as high as 123 lbs. per cubic foot. When this is compared with the dry, loose weight of the aggregates, plus bitumen, (about 100 lbs. per cubic foot) it is seen that a very dense and consequently impervious carpet was achieved.
The "shoulders" of the macadam pavement, for a width of 20 feet along each side of the runways were "feathered" down to a compacted thickness of 3/4". The inner ten foot strip was a combination of "coarse" and "fine" macadam, the former diminishing in thickness from 21" to 1-1 8′′ while the outer 10 feet was of "fine" macadam only. This gave a "fine" macadam feather of 2-18" to 3. 4′′ thickness in a width of 10 feet.
Final compaction of the macadam, "coarse" and "fine" was by power rollers of 10 tons weight after which, in the case of the Wearing Carpet, no doubt could be entertained as to the impervious nature of the work. This quality in the finished surface is, of course of great importance as the foundation remains dry under all conditions, ensuring, as far as possible, that undue subsidence will not occur.
The Barber-Greene Drying. Mixing and Spreading plant used in this work and described above is the "answer to the Engineer's prayer" so far as control of materials and work- manship in particular is concerned.
Calibration of the Mixer is by means of the "hot" gate opening and the two chain-driven sprockets of the Apron Feeder drive and Bitumen Pump.
Once these have been decided upon and duly set it is quite impossible for the ingredients of the macadam to be in any way rendered inconsistent. Any variation which may happen in the engine revolutions will not affect the Engineer's proportions but merely increase or decrease the output rate.
For Colour and Durability Use
The openings of the two "cold" gates at the Feeder are set after trial runs as it is only necessary to balance this rate of delivery to the Dryer with that of the "hot" gate, thus main- taining a constant head in the Mixer hopper.
Since the capacity of the plant is dependent upon the rate at which the Dryer is capable of removing moisture and transmitting heat into the aggregates, it is logical to start the procedure of mixing from this point. When the Engineer has determined the percentage of moisture in the aggregates to be used it is then only necessary for him to refer to a chart provided by the manufacturers to arrive at the permissible production rate. It should be remembered though that Specifications usually permit the Contractor to leave a maximum of 1% moisture in the aggregates after drying. Further tables are provided which give gate openings required for the passage of given tons per hour of aggregates, though practical "dry-run" tests are always made as a check.
do.
Facts and Figures
do.
11⁄2" Granite aggregate consumed ............... 20,000 tons approx. 3 8"
6,600 tons approx. 18" Dust aggregate consumed
TOTAL
4,400 tons approx.
31,000 tons approx.
1,560 tons approx.
60-70 Straight-run bitumen consumed R.C.2 Cut-back bitumen used for Tack Coat 20.000 gallons. Total value of work done
.HK$2,500,000.00 approx. Actual working period Wet weather allowance
9 months.
3 months.
As previously stated the actual mixing and spreading work began on 20th January, 1950, and from mid-April to the end of the work much interference by and due to rain was experienced. It frequently happened that one of Hong Kong's notorious short, sharp showers would saturate the working area in a few minutes and hold up work for several hours during which time otherwise ideal weather conditions prevailed.
These rains also had a very adverse effect on the rate of production at the mixing station as the aggregates became very damp causing a compulsory reduction in the rate of feed to the Dryer.
The finished runway is an excellent piece of work and reflects considerable credit to all concerned. A recent inspec- tion of the main runway on which heavy air traffic has been operating for almost a year revealed no defects whatever and users of the airfield have been unanimous in their praise of the operating surfaces.
The engineers for the project were the Port Works Office of the Public Works Department of Hong Kong, Mr. H. W. Forsyth, Executive Engineer, while the contractors were Messrs. Gammon (Malaya) Ltd., Singapore, for whom Mr. H. Lovett was the supervising engineer,
FENNER & ALDER'S
DOG
Famous
BRAND
PRINCE'S BLDG. HONG KONG
PAINTS, VARNISHES, ENAMELS, DISTEMPERS, ANTI-FOULING & ANTI-CORROSIVE COMPOSITIONS
Manufactured in England and Obtainable From
DAVID SASSOON & CO., LTD.
Sole Agents
42
Tel.
(34151 34152
Page 35Page 36
No comments yet.
Private notes are available after approval.