RILEM TC ISC-239 recommendation on reliable assessment of on-site concrete strength with NDT testing.
This paper adresses the most original issues that have been studied by the RILEM TC in order to achieve a reliable non-destructive assessment of on-site concrete strength. The assessment concerns the local strength, the mean strength and the standard deviation of local strengths. The recommendation is based on the two concepts of prescribed tolerance interval regarding the assessed parameter and of risk of wrong assessment. A minimum number of cores is available, which depends on the more or less ambitious estimation quality level (EQL), the repeatability of measurements (TRP) which must be quantified and the characteristics of concrete. The recommendation also covers the issue of selecting the core location (through conditional coring), choosing the conversion model (the bi-objective method is put forward), and checking the assessment error.