July_1971 — Page 37

that present day crushing strengths of around 40 to 50 N/mm2 (6000 to 7500 psi) could be greatly exceeded.

In order for this to happen, pre- fabrication must take over in local ferrocement construction just as it did in the widespread land uses in U.S.S.R. The writer firmly believes this because really significant improvements in strength and competitiveness of ferro- cement can only come from the close quality control possible in prefabrica- tion, which however, requires quantity production to be economically viable.

In prefabricated units, compaction could be accomplished by means of combined formwork vibration and pressure which would tend to produce a product of great uniformity. The comparatively smaller and more manageable prefabricated units could be also uniformly and optimally cured.

Assembly of these units would use modern concrete adhesives and pre- stressing. These methods would permit very low water cement ratios and high steel dispertions, cover could also be accurately maintained and a careful preassembly inspection, possibly com- bined with testing, made possible. The assembly could be very rapid, with only localized short duration protec- tion required during the jointing operations.

Conclusion

It is not generally known, even among engineers, that Jean-Louis Lambot a pioneer of reinforced con- crete construction patented his mate rial in 1855 for "mill-boats, barges, buoys, boats suitable for coastal traf- fic... most applicable for all struc- tures which tend to deteriorate where they stand whether in or out of water...".

Since that date leading engineers in Italy, Germany, France, Britain, Austria, U.S.A. and the Scandinavian countries have produced many sound and durable ship designs. Some mil. deadweigtht tons of concrete shipping were produced during World War II alone, mainly in U.S.A. It appeared however, that only during wartime conditions of steel shortage, could con- crete hulls be considered for ships in spite of the many advantages that they offered. The overriding consideration was hull weight, which for concrete ships of that era still remained too high.

Prestressing, incidentally, was then in its early stages of development and

Far East BUILDER, July 1971

BOAT

2. C

32 ft. ferrocement sloop built in Geelong, Australia, Hull is only 3/8in. thick apart from some pre-tensioned barges built by the Germans (and also some rather advanced hulls of shell design by Finsterwalder) – none was tried.

Yet the lessons of the old concrete ships should not be discarded, as they testify to the great durability of sea- going-concrete construction, and pro- vided useful experience in methods and materials.

Particularly noteworthy in respect to research and the numbers of float- ing units built is the Soviet effort, which although relatively less well known, continued unabated since 1921. Until the large scale introduc- tion of ferrocement its products were chiefly large and small rivercraft, light- ers, floating docks and pontoons.

In the early 40's, Nervi, who is generally credited with the invention of ferrocement, (although several en- gineers could also claim that title) began a new era of concrete at sea. At last his new material could compete with steel in weight. Most surprising of all, under certain conditions, ferroce- ment hulls could be made even lighter than steel.

Since the 40's concrete engineering has made considerable strides. In al- most every field previously dominated by metal construction, concrete is now able to offer at least one alternative.

The emergence of large scale use of this material has naturally been pre- ceeded by extensive and continuing research. Today, concrete, and espe- cially prestressed concrete is able to compete with steel in fatigue resis tance, precision of assembly, compres- sive strengths and quality control. Yet even now there are completely reason- ed and feasible proposals which would raise - by normal means the com- pressive strengths to pressive strengths to 100 N/mm2 (approx. 15,000 psi) and beyond, to name but one item.

Ferrocement although not as well researched as concrete, shares as a con-

crete product many of the positive aspects of the latter and offers some of its own, as well as a prospect of simple and cheap improvement. Wartime con- ditions of steel shortage may hopefully never again arise, but even in peace- time steel plate and sections' supplies may become too expensive or be cut off altogether.

The writer is convinced that ferro-

cement offers an economically attrac- tive alternative, which, with an increas- ed emphasis on research, could well originate a new industry in Hong Kong and be utilized both on land and in shipbuilding simultaneously.

Acknowledgements

Paradoxically the references are both too few and too numerous to quote. In the writer's opinion too few really serious English language refer- ences exist since little consistent re- search seems to have been carried out in Western countries.

By contrast, the countries of East- ern Europe have since about 1957 devoted considerable resources to fer- rocement research, and comparatively large numbers of tehnical references exist in Russian, Polish, and Czech.

As a further basis of this article the writer has been fortunate to secure several personal communications from Europe, America and Australasia which he came across during the course of his own research in HK University.

The writer would like to single out his indebtedness to the work of: Dr. B.R. Walkus of Lodz Technical Univer- sity, Poland and of Mr. R. Morgan of Bristol University in Britain, and would like to thank Professor S. Mackey, Head of Civil Engineering Department, H.K.U. for his kind com- ments and suggestions.

Reference: "Ferrocement; a sur- vey" by R. Walkus and T. G. Kowalski "Concrete" pp. 48-52 Feb. 71 Lon- don.

35