In literal meaning, uncertainty is a state of doubt about the result credibility. There are always be differences between true value and measurement result. In fact, measurement uncertainty characterizes the dispersion of the values that could reasonably by attributed to the measurand which states some information about quality of measurement. However, reporting test result with its measurement uncertainty is presented by the laboratories which could be achieved IEC/ISO 17025 certificate from the valid laboratory Accreditation Body (AB). In one hand, measurement uncertainty is estimated as the technical requirements of IEC/ISO 17025 in the mentioned laboratories ,on the other hand, in the rest of laboratories cannot be able to trust in presented results in terms of accuracy and precision in measurement due to lack of estimation of measurement uncertainty.
Determining compressive strength of concrete which is known as one of the most popular physical characteristics of concrete, is one of the most important criteria to accept or reject the test result of produced or executed concrete. In this way, concrete is graded in different categories which causes supervisors to be in doubt in accepting or rejecting the test result due to lack of estimation or correct determination of measurement uncertainty of the compressive strength of concrete by laboratories. It might be caused to make wrong decision and judgment in analysis and interpretation of the result. Therefore, in the current study, estimation of measurement uncertainty of the testing compressive strength of concrete with a process approach & Using the GUM in a case study of Taradod Rahnama Engineering CO. laboratory has been presented. To achieve this main objective, all the effective components of the testing compressive strength were identified and quantified then by using the GUM, in step by step to calculate combined uncertainty and finally expanded uncertainty. This study can be as an appropriate pattern to determine correct measurement uncertainty of the testing compressive strength of concrete in order to use in related laboratories to increase the result credibility and trust in presented results in terms of accuracy and precision in measurement.