Issue 31

A. Abrishambaf et alii, Frattura ed Integrità Strutturale, 31 (2015) 38-53; DOI: 10.3221/IGF-ESIS.31.04 40 flow direction. By assuming θ as the angle between the notched plane and the direction of the concrete flow, the notch plane was designated parallel for θ = 0 ° or perpendicular for θ = 90 ° . Since the core scheme was maintained for both panels, for each core location within the panel there were two cores with distinct notch directions, i.e. θ = 0 or 90º. This will enable to evaluate the influence of fibre orientation on the stress-crack width ( σ-w ) relationship. For instance, θ of A1 specimen is 90 ° and 0 ° in panels A and B, respectively (see Fig. 1). Twenty two cores were sawn to produce prismatic specimens to be used in the uniaxial tensile test with the dimensions of 110×102×60 mm 3 . Following the same notching procedure for the splitting test specimens, the prismatic specimens were notched according to parallel ( θ = 0 ° ) and perpendicular ( θ = 90 ° ) directions regarding the expected concrete flow. The notch was executed on the four lateral faces of the specimen, at their mid-height, with a thickness of 2 mm and a depth of 5 mm. Test setup: Splitting tensile test In a first stage, the σ – w relationship was assessed by carrying out splitting tensile tests. The recommendations of ASTM C-496 standard [12] were followed for this purpose. The tests were executed by closed-loop displacement control. To ensure a proper constant displacement rate, once the crack is initiated, a rather low value of the displacement rate, i.e. 0.001 mm/s, was applied. The crack opening width was averaged from the readouts of five linear variable differential transducers, LVDTs, which were mounted on the surface of the specimen, three on the top and two on the bottom surfaces, see Fig. 2. 10.0 65.0 65.0 10.0 150.0 37.5 37.5 37.5 37.5 LVDT Specimen 60.0 (a) (b) Figure 2 : Geometry of the specimen and setup of the splitting tensile test (dimensions are in mm): (a) specimen front view (top of the panel), (b) specimen lateral view. Test setup: Uniaxial tensile test The stress – crack opening width ( σ – w ) relationship was also directly ascertained through uniaxial tensile tests, which were executed according to the RILEM TDF-162 [13]. This test was carried under closed-loop displacement control, adopting the following displacement rates during the test: 0.005 mm/min up to a displacement of 0.05 mm, 0.02 mm/min up to a displacement of 0.1 mm, 0.08 mm/min up to a displacement of 0.5 mm, and 0.1 mm/min until the completion of the test. The test was controlled by the averaging signal received from the four LVDTs installed on the lateral surface of each prismatic specimen, see Fig. 3. 110 60 (a) (b) Figure 3 : Uniaxial tensile test setup: (a) specimen front view, (b) specimen lateral view (units in mm)