Ferrocement in Hong Kong
by T. G. Kowalski
A sudden interest in ferrocement as a construction medium has been spurred by the recent launching in Hong Kong of ferrocement fishing vessels. As a lightweight extension of reinforced concrete, it has many economic advantages and equally important technical advantages. In this article, Mr. T. G. Kowalski, CEng,MIStructE,MI(SA)CE, lecturer with the Department of Civil Engineering, Hong Kong University, shows how suitable the material is, both in ship construction and in normal building. The local labour and materials situa- tion, he says, favours its large scale use.
WHAT is ferrocement? First and fore- most it is a form of very high class reinforced concrete, whose thickness presently ranges between 10 to 40 mm (3/8in. to 1/2 in.).
The thicknesses which can be em- ployed are of importance to engineers, because reinforced concrete construc- tion in its present form has reached a practical limit in its pursuit of reduc- tion of self-weight - its greatest single drawback. Lighter artificial aggregates may still be produced, but it is diffi- cult to forsee that this would bring about a really significant saving in either weight or cost.
A more hopeful approach is to shape the material into "folds" which can support compression and bending by virtue of their shape and at the same time be appreciably thinner, and therefore lighter, than the present-day constructional forms in reinforced
concrete.
The material to achieve this must really be a form of sheeting, capable of being extruded and folded. It will, by this same process, become more uni- form in its internal structure, which will in turn enable it to be considered as a quasi-homogeneous material. The implications of the above could indi- cate a new philosophy of design and exiting new possibilities for reinforced
concrete.
Regarding the all important thick- ness, it is seldom desirable to go be- yond 40 mm. This is because of the uniform reinforcement usually requir ed throughout the section, its high cost, and also because of the difficul- tics which are experienced in compact- ing the concrete through fine mesh.
In reinforced concrete we erect formwork, place reinforcement (sel- dom smaller than 6 mm (1⁄44in. dia.) and
Far East BUILDER, July 1971
pour concrete into the forms with the usual aggregate size of 20 mm (in. approx.) and over.
In in-situ ferrocement we erect a series of rigid pipe or other steel form- ers on which we drape ordinary rein- forcing bars, and follow up by "cloth- ing" the latter (on both sides of these bars) with several layers of fine dia- meter, closely spaced, square or hexa- gonal mesh, which is often galvanised. The wire spacing of this mesh is often 12 mm (in.) and its diameter varies between 0,5 to 1,2 mm. After the con- crete hardens, the pipe formers may be left in as permanent stiffening.
The procedure in pre-fabricated ferrocement elements is similar, but for the one-sided shuttering which is usually left out “in-situ”.
Perspectives
There should be no difficulty in producing high class ferrocement in Hong Kong. The territory as a whole possesses both the expertise and an adequate supply of local materials. Moreover, reinforced concrete has long been the dominant medium of con- struction.
Ferrocement is all the more rele- vant because there is neither a local
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"Photo"
Prefab, ferrocement elements on Nervi's Palazzo dello Sport in Rome. Shown prior to concreting, the elements act as both shutters and reinforcement
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