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Technical Note (National Research Council of Canada. Division of Building Research), 1961-10-01
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RILEM Symposium on the Durability of Concrete Held in Prague, 1961
Legget, R. F.
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DIVISION OF BUILDING RESEARCH
NATIONAL RESEARCH COUNCIL OF CANADA
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NOT FOR PUBLICATION FOR INTERNAL USE
PREPARED BY PREPARED FOR ｒｾ F. Legget Record purposes CHECKED BY APPROVED BY October 1961 SUBJECT
RILEM SYMPOSIUM ON THE DURABILIT Y OF CONCRETE HELD IN PRAGUE; 1961.
Problems relating to the durability of concrete are no respecters of curtains, iron or otherwise. This was well shown at a Symposium on the Durability of Concrete held recently in Prague, Czechoslovakia. Sponsored by RILEM, the international association of building material laboratories, the conference was organised by the Czech Institute of Theoretical and Applied Mechanics, a constituent
part of the Czechoslovakian Academy of Sciences. Professor St. Bechyne, Member of the Czech Academy and President of RILEM, presided at
the Symposium, and also at the preceding annual meeting of the RlLEM Permanent Commission. The Conference was splendidly housed in the main building of the Philosophical Faculty of the ancient University of Prague, in the centre of the old city. Attended by about 400 members, the conference taxed the capacity of the largest assembly hall available. Less than one third of those present were from western countries, with only four members from North America. Despite this, English was the main language of communication, the fluency of many of the Czech scientists and engineers at the meeting being notable. Simultaneous translation facilities were available. In all respects, therefore, the meeting was indistinguishable from a similar conference in the west.
The similarity was especially noticeable in relation to the technical content of the meeting, and of the papers prepared for ｩｴｾ
The problems met with in the use of concrete in the iron curtain countries are exactly the same as those of the west; the solutions are generally similar. A dominating impression was that just as North American engineers are liable to neglect the literature of Europe in background
reading for their own researches, so the engineers of eastern European countries did not seem to be too familiar with the corresponding literature
of North America. Most of the topics discussed at Prague have received
attention at meetings of the American Concrete Institute or of Committees
Cl and C9 of the American Society for Testing and Materials. There
were, however, many fresh approaches and much information presented regarding actual field experiences that will add notably to the world-wide store of knowledge in the field of concrete technology.
Many of the papers prepared for the Symposium were pre-published in printed form (see later); others were available at the meetings and many brief contributions were made in the discussions at
the conference which extended through three days. The subject was broken
down into four parts but, somewhat naturally, there was a good deal of
inevitable overlapping between the four sections. Theoretical problems
of the durability of concrete was the first main theme, followed by the mechanics of the disintegration of the normal texture of concrete as a
closely allied grouping. Tests and control of the durability of concrete
was the third subdivision, and associated with it was the fourth main
subject - the composition and manufacture of concretes. with long durability. Experience obtained with concrete structures in service was the subject of the fifth group of papers but papers in the other sections inevitably touched upon field experience also.
Durability was defined by Dr. L. Palotas of Budapest in one
of the excellent summary papers presented at the meeting as "the resistance of the materials or of the structures put up by them to all loads, forces, motions or effects of other kind acting on matter or on the structures,
in the course of their normal, regular use." In addition to the methods
normally used in North America for durability testing, attention was directed to a combined chemical and freezing test method, advocated by
Dr. W. Gaca of Poland and Prof. Inge Lyse of Norway. One such test
involves immersion of test specimens in sea water with a five-fold
concentration and then subjection to regular freeze -thaw cycles. It was
suggested that results obtained in this way give a reasonably good indication of durability after seven days.
A new method of assessing aggregate-cement bond was described by Dr. O. Valenta, of the host Institute in Prague, who served as the
very efficient secretary of the Symposium. A prism of concrete is broken across and a new prism of cement paste is then cemented to the fractured
surface. The permeability and strength of the new interface are then
measured, before and after freezing cycles, and the results were said to
give useful and reliable results.. There was naturally much discussion about
the significance of water absorption tests and the degree of saturation at
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-the real significance of freeze-thaw tests, and little discussion of -the correlation of such tests with actual exposure conditions. This clearly relnains as a fertile field for further research. Attention was directed . by several speaker s to the significance of cracks in considerations of
durability and some Soviet research work on the study of the effect of controlled cracking was reported.
From Poland came an interesting report by Dr. E. Janczewski of some unusual concrete deterioration definitely traced to biological action. The trouble was fir st noted in the concr ete linings of some galleries constructed in 1952 and 1953 in connection with pr eliminary work for the Warsaw subway. The galleries are located from 40 to 60 metres below ground; composition of the concrete, made with ordinary portland cement was approximately 1: 1 :2. The concrete was placed against unimpregnated boards of pine as formwork, and the boards were left in place between concrete and soil. After between 3 and 4 years, desintegration of the concrete in the galleries was first noted. An
intensive investigation revealed that it was due to the fungi Merulius lacryrnans and Poria vaporaria commonly known as wood-destroying bacteria. Although the concrete provides no nutrient f<:>r the fungi, they are able to penetrate solid concrete in search of food and light,
causing considerable damage in so doing not only by mechanical action but also by the secretion of organic acids.
From the U. S. S. R. came an account of the frost resistance of heat treated concrete in a paper by Prof. S. A. Mironov. In 1961, almost 40 million cubic yards of precast concrete units will be produced in
Soviet precast plants and will practically all be heat treated, either by autoclaving or by steam curing. Electric curing of monolithic concrete structures is also achieved in the field in the winter by heating reinforcing steel. Tests have shown conclusively the advantage given in durability by autoclaving over ordinary steam curing. Typical figures are those given from experiments by N. A. Popov and A. V. Chuiko with identical samples which withstood over 200 cycles of freeze-thaw testing after autoclaving but which showed a loss of strength of from 27 to 36 per cent, and surface deterioration, after only 100 cycles following ordinary steam curing. Professor Mironov also reported that some of his colleagues had shown that the best additive for increasing the frost resistance of heat-treated concrete is an organic silicon compound in the form of an aqueous
emulsion, described as a polysiloxan fluid.
The significance of careful examination of concrete structures after appreciable service was stressed by several speakers. Reference was made to the satisfactory performance of the fir st British building of reinforced concrete, a house built under Wilkinson's original patent at Newcastle-upon-Tyne about 1865, and recently demolished. A British
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-gasholder built in 1892 of concrete is still glvmg good service. A wide variety of more recent concrete structures was described, from a number of European countries; the records thus presented will be found to be a singularly valuable part of the two volumes that will provide a permanent record of the Prague conference. One case only can be briefly mentioned, this being the demolition of a Czechoslovakian highway bridge that had been in service for 36 years when it had to be removed in connection with
some railway reconstruction. Mr. M. Ciganek of Brno was in charge of the work and described it to the conference. The bridge was a through tied arch with a span of 135 ft and a weight of about 650 tons. It had to be demolished without any interference with the railway tracks it spanned. - A steel bridge was therefore ｣ｯｮｳｴｲｵ｣ｾ･､ above the roadway of the concrete
arch, extending beyond it over one abutment. The concrete arch was then suspended from the steel bridge and slowly edged off its original supports, being then moved by steps, the part that overhang the original abutment being demolished between each move. The demolition job was successfully completed but, of more importance, a detailed inspection of the bridge was made during each phase of the demolition. No cracking of the concrete was found and no corrosion of the steel reinforcement, despite the severe conditions to which it had been exposed over railway trjicks carrying steam locomotives. Many samples of the concrete and steel, obtained from
the breaking-up process, were tested in the laboratory, and so a complete picture was obtained of the exact condition of concrete and steel after its 36
years of service.
The volume containing the papers presented to the conference submitted in advance of the meeting was published by Nakladatelstvi,
Ceskoslovenska Akademie Ved, Prague, 1961, having 394 pages and many illustrations. (Copies may be obtained from AR TIA, P. O. B. 790,
Prague, Czechoslovakia; unfortunately no price is marked on the book. ) The volume contains twenty-seven papers, two only on experiences with actual structures, the others divided roughly equally between the four main group subjects (already noted). Twelve of the papers come from "iron-curtain" countries and fifteen from western countries, including Japan. It is significant that, in this volume printed and published in Prague, twenty of the papers are in English, and seven in French, these being the two official languages in which RILEM conducts its business. Proceedings of the conference itself, discussions, and later papers, will appear later in a companion volume to be issued by the same publisher.
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-RILEM
Full Title: Reunion internationale des Laboratoires d'essais et de Recherches sur les Materiaux et les Constructions.
In English: The International Union of Testing and Research Laboratories for Materials and Structures.
Headquarters: 15 Rue Brancion, Paris. Secretary-General: M. R. L'Hermite.
