Energy-based correlation between en 14651 beam and panel tests for fiber reinforced shotcrete used in tunnel linings

The use of fiber-reinforced shotcrete (FRS) as a structural support material in tunnelling has increased significantly in Latin America following its recognition in the fib Model Code. However, the characterization of fiber-reinforced concrete (FRC) remains challenging in many regional projects due to the limited availability of closed-loop control systems required for the EN 14651 three-point bending test. As an alternative, the square panel test, based on energy absorption capacity, is widely used for quality control of FRS, although it does not directly provide the residual strength parameters required for structural design.This paper presents an energy-based methodology to correlate EN 14651 beam tests with square panel tests, enabling the estimation of residual strengths from energy absorption capacity. Flexural toughness was defined as the area under the load–CMOD curve, from which equivalent strengths and equivalent strength ratios were derived. These parameters were correlated with the energy absorption capacity obtained from square panel tests. The proposed relationships were established using experimental programs conducted on concrete reinforced with 48 mm and 54 mm macro-synthetic fibers at different dosages. Linear correlations between flexural toughness and panel energy absorption, together with nonlinear relationships between equivalent strength ratios and fiber volume fraction, were obtained and statistically evaluated.Within the experimental range investigated, the proposed methodology showed satisfactory agreement with the experimental results, with residual strength prediction differences generally within ±17%. The results indicate that the proposed framework may provide a practical approach for relating panel-based quality control with EN 14651 residual strength parameters used in performance-based design of FRC tunnel linings. However, the proposed correlations depend on the fiber type and post-cracking response of the FRC and therefore require calibration for each specific fiber-reinforced concrete.