Sürdürülebilir Kalkınma Amaçları
Yayınlar
- MakaleAçık Erişim2026Variability of Schmidt Rebound Values in Volcanic Rocks (Basalt and Lapilli Tuff): Comparative Effect of Surface Roughness, Alteration, and Testing Methods
Karaman, Kadir; Külekçi, Gökhan; Çakır, Yaşar; Kolaylı, Hasan
Enhancing the sustainability and safety of rock engineering requires understanding how micro-structural and alteration conditions influence the geomechanical properties of rocks in geotechnical projects. The determination of surface hardness using the Schmidt Hammer is an interdisciplinary experimental method employed in mining, geology, and civil engineering. This study quantitatively evaluates the effects of surface roughness, weathering degree, and evaluation procedures on Schmidt rebound values obtained from basalt and lapilli tuff. Field measurements on eight surfaces produced rebound values between 10 and 60, with standard deviations ranging from 2.4 to 11, reflecting substantial variability related to roughness and alteration. Laboratory results showed that cut surfaces yielded the highest hardness values (Mean ≈ 57–58) with very low variability (SD ≈ 1.1–1.6), whereas natural surfaces exhibited markedly lower rebound values (Mean ≈ 19–22) and greater scatter (SD ≈ 4–4.5). A strong correlation (R2 > 0.97) was observed between JRC roughness and rebound values in laboratory-prepared samples. The percentage difference among the USBR, ASTM, and Sumner & Nel methods remained below 5% when the standard deviation of measurements was under 2, indicating that method selection becomes critical only for heterogeneous surfaces. Mineralogical heterogeneity further increased variability in lapilli tuff, whereas basalt provided highly consistent responses. Overall, this study introduces quantitative thresholds linking roughness, weathering, and statistical variability, offering a more rigorous and reproducible framework for interpreting Schmidt hardness measurements.
- MakaleYalnız künye2014Assessment of strength properties of cemented paste backfill by ultrasonic pulse velocity test
Yilmaz, Tekin; Ercikdi, Bayram; Karaman, Kadir; Külekçi, Gökhan
Ultrasonic pulse velocity (UPV) test is one of the most popular non-destructive techniques used in the assessment of the mechanical properties of concrete or rock materials. In this study, the effects of binder type/dosage, water to cement ratio (w/c) and fines content (<20 μm) of the tailings on ultrasonic pulse velocity (UPV) of cemented paste backfill (CPB) samples were investigated and correlated with the corresponding unconfined compressive strength (UCS) data. A total of 96 CPB samples prepared at different mixture properties were subjected to the UPV and UCS tests at 7, 14, 28 and 56-days of curing periods. UPV and UCS of CPB samples of ordinary Portland cement (CEM I 42.5 R) and sulphate resistant cement (SRC 32.5) initially increased rapidly, but, slowed down after 14 days. However, UPV and UCS of CPB samples of the blast furnace slag cement (CEM III/A 42.5 N) steadily increased between 7 and 56 days. Increasing binder dosage or reducing w/c ratio and fines content (<20 μm) increased the UCS and UPV of CPB samples. UPV was found to be particularly sensitive to fines content. UCS data were correlated with the corresponding UPV data. A linear relation appeared to exist between the UCS and UPV of CPB samples. These findings have demonstrated that the UPV test can be reliably used for the estimation of the strength of CPB samples.