Conversion Factors between Non-Destructive Tests of Cubic and Cylindrical Concrete Specimens

Assessment of existing structures is an essential topic for engineers working in the field of construction in most industrial countries. Evaluation of compressive strength is one of the most critical factors for concrete structures. Non-Destructive Testing (NDT) techniques are the most extensively used techniques for the prediction of compressive strength in the existing concrete structures. Among NDTs, ultrasonic pulse velocity and rebound hammer are more common to predict the compressive strength of the concrete. This study also investigates surface electrical resistivity as an NDT.  In many studies, concrete specimens are constructed in cubic or cylindrical shapes, but the role of conversion factor has been overlooked that may change the NDT results from cubic to cylindrical specimens and vice versa. Hence, in the present paper, an experimental study was conducted on concrete specimens based on NDTs. In this experimental process, cubic and real cylindrical specimens were assessed in the same mix designs at the ages of 7, 28, and 90 days. Herein, some accurate equations were also proposed to convert NDTs and compressive strength of cubic concrete specimens to cylindrical specimens based on experimental data and response surface methodology. Results showed that the proposed equations perform sufficient accuracy for the conversion intended.