The determination of concrete strength and grade

Abstract

In the paper the experience of the Buildings and Structures Design Research Department study of the controversial issues of concrete grade and compressive resistance is summarized. The main indicator of concrete quality in the concrete and reinforced concrete prefabricated and cast-in-situ structures is the compressive strength of concrete, which corresponds to its specified characteristic strength. The analytical and graphical representations of this indicator are well known. In the existing normative base its ambiguous interpretation at the stages of concrete composition selection, product manufacture and buildings and structures operation causes the conflict of economic interests between such involved parties as concrete manufacturer, builder and investor. The problem of the definitive interpretation of the results of concrete strength destructive and nondestructive tests can be solved only under the condition of the current standards revision and harmonization. The analysis and examples of the use of normative base, which is effective for concrete producers and consumers, for the concrete strength and grade determination, and of the concrete strength and grade determination directly in structures are presented. Some instances of unsubstantiated strength assessment are given, when the non-destructive mechanical and ultrasonic methods, as well as the control samples are used in disregard for regulatory requirements. For the structures operation it is essential to ensure the actual concrete strength grade specified by the project. For its reliable determination, the drilled concrete core samples and calibrated non-destructive methods have been used. The various methods of the cores strength tests results assessment have been exemplified. The method for the tests interpretation by individual results or by their groups requires an  unambiguous determination.