Application of WST-method fore fracture testing of fibre-reinforced concrete

To evaluate the reproducibility of the wedge-splitting test method and to provide guidelines, a round robin study was conducted in which three labs participated. The participating labs were: § DTU – the Technical University of Denmark, Department of Civil Engineering; § CTH – Chalmers University of Technology, Department of Structural Engineering and Mechanics; and § SP – the Swedish National Testing and Research Institute.

Two different mixes were investigated; the difference between the mixes was the fibre length (Mix 1 with 40 kg of 35 mm long fibres and Mix 2 with 40 kg of 60 mm long fibres). The test results from each lab were analysed and a study of the variation was performed. From the study of the intra-lab variations, it is evident that the variations of the steel fibre-reinforced concrete properties are significant.

The coefficient of variance for the splitting load was found to vary between 20 to 40%. The investigation of the inter-lab variation, based on an analysis of variance (ANOVA) indicated that there is no inter-lab variation. The test result can be said to be independent of the testing location and the equipment used (with or without CMOD-control).

The conclusions that can be drawn from this study are that: § the wedge-splitting test method is a suitable test method for assessment of fracture properties of steel fibre-reinforced concrete; § the test method is easy to handle and relatively fast to execute § the test can be run with CMOD-control or without, in a machine with a constant cross-head displacement rate (if rate is equal to or less than 0.25 mm/min); § due to variations in fibre distribution, the scatter of the test results is high; § the dimensions of the specimen (height, width, and thickness) should, if possible, be four times the maximum fibre length, or at least more than three times the fibre length; § using inverse analysis, the tensile fracture properties can be interpreted from the test result as a bi-linear stress-crack opening relationship.