Comparative Analysis of the Accuracy of NDTs in Determining Concrete Strength

In evaluating the effectiveness of various nondestructive tests (NDTs), the results obtained through ultrasonic pulse velocity and the Schmidt hammer were compared on concrete cylinders, manufactured with a 4000 psi mix, evaluated at 7 and 28 days. Correlation equations were developed to relate the results of these NDTs with the actual concrete strength, obtaining $R^{2}$ values ranging from $17.8 \%$ to $52.7 \%$. The results indicated that the Schmidt hammer showed a stronger correlation with compressive strength, reaching a maximum $R^{2}$ of $52.7 \%$, while the ultrasonic pulse velocity showed a maximum $R^{2}$ of $34.9 \%$. Additionally, moisture was found to significantly influence the results of both tests, affecting both pulse velocity and rebound number. These equations provide useful tools for engineers, allowing them to assess concrete strength more accurately without the need for sample extraction, thus optimizing inspection and maintenance processes for structures.