No_1_1960 — Page 55

The advantages of rubber duct tubes in pre stressed concrete con- crete can be listed as follows:

(1) The duct so formed in the concrete enables a first-rate bond to be established between grout and

concrete.

(2) Casting can be done prior to delivery of the pre-stressing cables and, owing to the excellence of the duct, no difficulty should be countered in threading the cables.

(3) Speed of operation.

en-

(4) Easy storage the tubes be- ing rolled up and housed in a small space.

There is, in addition to the tube described. a method of forming ducts by the use of rubber formers of rectangular section which are made rigid in the formwork by mild steel bar inserted in a central

a

When

rod

hole throughout its length. the concrete is cast, the steel first, and then the rubber former, is extracted.

The first occasion on which 6-in. rubber tubing was used to form sur face water drains in concrete haunching was in Autumn, 1952, at St. Johns Hill, Shaftesbury, by the Roads and Bridges Department of the Dorset County Council. It has since been adopted by nine English County Councils and it al so enjoys considerable use overseas. This is especially so where alterna- tive traditional materials are not available locally and are expensive to import.

The value of this particular ap- plication consists not only in its economy in both labour and ma- terials, but in the advantages of jointless monolithic

concrete

con-

struction, This ensures a good hydraulic flow.

a

Many users construct porous drains by laying to falls a dense concrete bottom to a trench and bedding-in duct tubes to form slight indentation while it is still porous concrete is then poured above this and when the rubber tube is withdrawn the duct forms an effective drain.

in the concrete green. "No-fines"

The author is indebted to the Ductube Company Limited of Lon- don for their help in the prepara- tion of this article, also to the Stressed Concrete Design Company of London for information regard. ing solid rubber duct formers.

(This is the first part of a two-part article issued by the Natural Rubber Development Board).

LEE YU KEE

LIMITED

SANITARY ENGINEERS AND PLUMBING CONTRACTORS

L-17 MAN YEE BUILDING, HONG KONG. PHONES: 36043, 36044

Non-corrosive Rigid P.V.C. Pipes and Fittings for all kinds of Water Services Especially for Salt Water and Chemical purposes.

MALAYAN DRILLERS (HK) LTD.

We Specialize in:

• Tube Wells for Independent Water Supplies.

•

Diamond Core Drilling.

• Site Investigation and Foundation Testing.

Pressure Cement Grouting.

•

Soil Mechanics.

Apply MALAYAN DRILLERS (HK) LTD.

PHONE: 26307.

ROOM 605, BANK OF CHINA BLDG.

HONG KONG.

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