REBOUND HAMMER TEST

This study presents a comparative evaluation of the strength characteristics of concrete using both non-destructive (rebound hammer) and destructive (compressive strength) testing methods. The primary aim of the research was to determine the correlation between rebound hammer readings and actual compressive strength values of concrete produced from different mix ratios; 1:2:4 (C20), 1:1.5:3 (C25), and 1:1:2 (C30) under proper compaction and curing conditions. The investigation was motivated by the need to establish a reliable, quick, and non-invasive method for assessing the in-situ strength of concrete structures while maintaining compliance with international testing standards. The experimental program involved casting 100 mm × 100 mm × 100 mm concrete cubes for each mix ratio. The cubes were cured for 7, 14, and 28 days, after which they were tested using a Schmidt rebound hammer in accordance with BS EN 12504-2:2012 and ASTM C805, and a compressive testing machine following BS EN 12390-3:2019. In addition, a sieve analysis was performed on both fine and coarse aggregates to determine their particle size distribution and compliance with BS 812 (Part 103.1:1985) standards. Statistical regression analysis was also conducted to develop mathematical relationships between rebound number and compressive strength, and to determine the coefficient of determination (R²) for each mix ratio. The results indicated that concrete strength increased consistently with both higher cement content and longer curing periods. At 28 days, average compressive strengths of 17.89 N/mm², 25.92 N/mm², and 31.52 N/mm² were recorded for C20, C25, and C30 grades respectively. The rebound hammer results were found to underestimate compressive strength by about 5–10%, but showed a strong correlation, with R² values of 0.85 (C20), 0.96 (C25), and 0.98 (C30). The findings confirm that while the rebound hammer test cannot replace compressive testing for structural verification, it is a valuable non-destructive tool for rapid field assessment and comparative strength evaluation. Proper calibration using laboratory data is essential to ensure reliable application in insitu concrete quality control