Assessment of the factor <i>κ</i> _k,max in classification of steel fiber‐reinforced concrete

Abstract This paper presents a general approach, and results employed in a study aimed at assessing the value of a coefficient, κ k,max , introduced in Annex L in EN 1992‐1‐1:2023 (EC2). This coefficient defines an upper limit of the ratio between steel fiber reinforced concrete (SFRC) characteristic and mean values of the residual tensile strengths, f R1 and f R3 . It is introduced in the code to avoid design strengths that in quite a few cases may be non‐conservative when derived from relatively small samples (e.g., of six notched beams). While it is intended that the mean strength would be pre‐documented by the concrete manufacturers it is not always available. This study aims to assess κ k,max for such cases. The methodology of the study was based on taking large samples from six batches of SFRC mixes with 20 and 40 kg/m 3 steel fibers, supplied by three local concrete manufacturers (altogether, 200 notched beam specimens). Stress–Crack (notch) Mouth Opening Displacement curves were obtained from specimens of each large sample and then an exhaustive combinatorial analysis was performed of all possible different combinations of sub‐sets of six specimens. The value of κ k,max was then evaluated from the data of the large samples and of their corresponding sub‐sets. Findings of this study support the 0.6 value set in EC2 and show that in the absence of the manufacturer pre‐documentation, the characteristic SFRC residual strengths can be evaluated also based on the mean strength measured from a small sample. The current data also indicates that the increased value of 0.7, allowed by EC2 for samples with relatively small scatters, may need further investigation.