Methods of determining strength and other properties of concrete in dams

Abstract

Knowledge of the real properties of concrete in a structure and their changes during service permits solving many important problems related with the design of reliable, durable, and economical dams of different types. Such problems include an estimate of the correspondence between actual properties of concrete in a structure and the properties accepted when designing and the degree of reliability of determining strength and other qualities of concrete in dams by different methods.This problem has been studied in the International Committee on Concrete for Large Dams and a number of participating countries (France, USA, Great Britain, Japan, Norway, Australia, Czechoslovakia, and Sweden) have presented their opinions on this matter. The International Committee of Concrete has made a report on these data (September, 1967) and presented it to the 9th Congress on Large Dams. The main features of the report and conclusions are given below.In order to determine the behavior, life, and reliability of a dam after a certain service period it is necessary to know not only the concrete strength but also a large complex of other properties and their changes in time and under the effect of external factors. Therefore, reliable and well-founded methods of estimating the properties of concrete in structures are needed. A comparison of the views held in various countries concerning the value of methods and their areas of application permit making certain general conclusions with regard to the problem in question.Inspection and Testing of Outside Surface of Concrete Structures. The condition of a structure and the concrete properties are estimated first of all by a careful visual inspection of the dam and by determination of the strength of its outside surfaces. Such an inspection reveals the directions of a more detailed study and should be accompanied by a study of the documents on the composition of cement and concrete, and of observations during concreting, and also by tests of control samples.Instruments designed to determine the impact strength of a concrete surface are often used in practice for testing outside surfaces. Experience in Russia and abroad has shown that this method is useful mainly for detecting poor concrete situated near the surface and therefore is regarded as a supplement to other methods. It can be used also for a comparative estimate of the behavior of surface layers of concrete in parts of structures subject to alternate freezing and thawing, and is an auxiliary means of determining the degree of frost action on concrete.Coring and Sawing of Large Concrete Specimens. Large sections of concrete are cut out by drilling or other methods, which are then machined to impart the proper shape and tested for compressive strength. In Japanese practice this method is considered most reliable.