Editona/ Comment

Editorial c o m m e n t To widen the scope of this editorial commentary, the Editor has invited the members of the Editorial Advisory Board to contribute their views from time to time on aspects of the subject that are of especial concern to them. The first to do so is Dr. Andrew Short, who is Honorary President of the Euro-lnternational Committee for Concrete. Currently he is playing an active part in international codification and has a particular interest in lightweight concrete construction.

S. C. C. Bate

SOME NOTES ON INTERNATIONAL CODE WORK FOR LIGHTWEIGHT CONCRETE CONSTRUCTION Lack of insularity is not indeed one of the merits or faults attributable to the majority of the British civil engineering community, nor is NIHS ('the not invented here syndrome') absent in our midst, any more than in all other European countries. Insularity in technological matters is certainly not an exclusive British character- istic; it is equally present in France, Germany, the USA and elsewhere. Such attitudes, however, are obviously not in accord with the basic philosophy of the founding fathers of the European Communities and seems to have lost much of its persistence in recent years.

It has been recognised that the research results and conclusions from practice and experience, accumu- lated in research institutes and universities, in design offices and on construction sites during the inter-war and post-war years should be examined, synthetised and made available in a practical, yet scientific and systematic way for the international community of civil engineers. This is indeed the professed aim of the Euro- International Committee for Concrete (CEB), founded some 25 years ago on the ,initiative of French engineers but supported with great energy by a number of eminent British engineers and sponsored by the Institution of Civil Engineers, the Institution of Structural Engineers, the Concrete Society, the Cement and Concrete Association, and the Building Research Stat'ion. Through the suc- cessive editions of its CEB-FIP International Recom- mendations for Concrete Construction culminating in the International Model Code published in 1978, and through the publication of working papers in more than 130 Bulletins, CEB has greatly influenced the technical contents and style of most national codes of practice for various types of construction, including the calculation of their safety, throughout the world.

The 1970 editions of the International Recommend- ations included for the first time, provisions for light- weight aggregate concrete for structural use. In 1977 the CEB-FIP Manual of Lightweight Aggregate Concrete Design and Technology was published and represents a synthesis of the most up to date knowledge on this subject, a comprehensive state-of-the-art report. Simi- larly, the CEB-FIP Manual on Aerated Concrete Construc- tion is an authoritative statement on the structural use of this material.

Until recently, lightweight concrete was regarded as a new and as yet untried structural material. Code drafting committees and in particular the International Workiag Commissions of CEB were consistently cautious in applying known facts and experience in the recom- mendations and rules in their publications. Lightweight aggregate concrete was regarded as a different material from concrete made with gravel or crushed rock aggre- gate, and in view of the difficulties experienced by struc- tural engineers with novel materials and innovations, the use of lightweight aggregate concrete for structural purposes was surrounded by a plethora of technical taboos and prudent restrictions. In the face of these difficulties, however, the new material has established its reliability and technical usefulness, and it is now justi- fiably regarded as one of the 'traditional' accepted building media.

Engineers experienced in modern practical light- weight aggregate concrete construction consider almost unanimously that the restrictions and warnings imposed initially on the designer by current national and inter- national codes of practice and building regulations are no longer necessary in the light of present knowledge and experience, and that it would therefore be reason- able to regard structural lightweight concrete as in every way equivalent to normal concrete construction. It will, of course, still be necessary to bear in mind that many types of lightweight aggregate are being produced and that the properties of the concrete made with them differ. More detailed information should therefore be made available by the producers concerning these properties, eg their modulus of deformation, their creep and shrink- age properties, the relationship of their tensile and com- pressive strengths, their bond properties.

It is probable that the Complement to the CEB-FIP International Model Code to be published in 1981 with the support of the Building Research Establishment, wilt no longer contain the restriction that made the applica- tion of lightweight concrete previously somewhat complicated. Similarly, the proposed draft Eurocode No. 2 on Concrete Construction now being prepared, will contain the minimum of restrictions for lightweight con- crete compared with normal aggregate concrete.

Greater freedom for the designer clearly requires, however, greater care and intelligent appreciation, both in design and on the construction site, of the probable pitfalls which can hit both lightweight and normal aggre- gate concrete structures. One of the raison d'~tres of the present series should be to achieve and facilitate just that.

Andrew Short

69