TAGRA 2025

Ultrasonic Pulse Velocity and Schmidt Hammer methods, being non-destructive testing (NDT), carry certain limitations and may also yield different results due to factors originating from the concrete's microstructure. In this study, strength measurements were performed using both methods on produced mixtures, taking into account some frequently changed concrete parameters in practice, and the accuracy of non-destructive methods was examined using data obtained from axial compression tests. For this purpose, concretes of different classes were produced by varying the water/cement ratio (W/C) and cement content (C), and these concretes were stored in various curing environments (water, air, and humidity). Maximum aggregate particle diameter (8 mm, 16 mm, and 22.4 mm) was also determined as a parameter in the study. Air content, unit weight, and slump tests were conducted as fresh concrete tests in the study. Hardened concrete tests were conducted on a total of 54 cube samples measuring 15×15×15 cm³. The compressive strengths of the samples on days 7, 14, 21, and 28 were determined using non-destructive methods. The reference compressive strength values were obtained by subjecting the 28th-day samples to axial compression testing.

The findings revealed that continuous water curing significantly enhanced strength development, with water-cured samples exhibiting up to 30% higher compressive strength at 7 days compared to air-cured samples. The performance difference diminished but remained significant at day 14. Furthermore, smaller aggregate sizes (8 mm) provided more uniform results and higher UPV correlations, while larger aggregate sizes (22.4 mm) provided higher absolute compressive strength but greater variability in NDT predictions. These results highlight the need for careful control of both curing and aggregate size to ensure structural performance and reliable non-destructive strength prediction.