Issue 31

A. Abrishambaf et alii, Frattura ed Integrità Strutturale, 31 (2015) 38-53; DOI: 10.3221/IGF-ESIS.31.04 41 Results and discussion: Splitting tensile test Fig. 4 depicts both the envelope and average force – crack mouth opening response ( F – w ) obtained from the splitting tensile tests, when the notch direction was parallel ( θ = 0 ° ) and perpendicular ( θ = 9 0 ° ) to the concrete flow direction. During the first phase of the test, the F - w relationships were almost linear up to the load at the crack onset, since the LVDTs recorded the elastic deformation of the SFRSCC specimen. Therefore this deformation should have been removed from the F - w curves, however since this deformation was marginal it could be neglected. After the crack onset, two distinct behaviours were observed for the θ = 0º and 90 ° series. Regarding the θ = 0º series (Fig. 4(a)), the composite exhibited a non-linear hardening behaviour until the peak load was attained, followed by a softening phase. On the other hand, for θ = 90º series it was observed just a softening phase immediately after the crack onset. Briefly, these differences between the θ = 0º and 90 ° series could be ascribed to rather distinct number of fibres intersecting the crack plane at the specimens’ notch, due to a preferential fibre alignment perpendicular to the concrete flow direction. The higher number of fibres at the crack plane of the θ = 0º series specimens will promote a higher stress transfer grade between the crack surfaces and, consequently, higher post-cracking residual forces. The aspects related to the fibre distribution / orientation will be detailed further ahead. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 10 20 30 40 50 60 70 80 Envelope Average Force (F) [kN] w [mm] 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 10 20 30 40 50 60 70 80 Envelope Average Force (F) [kN] w [mm] (a) (b) Figure 4 : Force – crack opening width relationship, F – w, obtained from splitting tensile test for: (a) θ= 0 ° and (b) θ = 90 ° . In general, the F – w relationship showed a high scatter. However, in the case of SFRSCC the scattering in the results was expected since the mechanical behaviour of this material was significantly dependent on the fibre dispersion/orientation, even for specimens with same geometry and from the same batch. Moreover, in this particular case the relatively high scatter could also be enhanced because the specimens were extracted from different locations of the panels, i.e. with distinct distances from the casting point. Note that during the casting of the panels, the fibre distribution /orientation was influenced by the viscosity and velocity of the fresh concrete along the flowing process. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0 10 20 30 40 50 60 70 Top Average Bottom Force [kN] w [mm] 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0 10 20 30 40 50 60 70 Top Average Bottom Force [kN] w [mm] (a) (b) Figure 5 : Nominal tensile stress – crack opening width relationship, σ– w, obtained from splitting tensile test for the two sides (top and bottom) of the specimens: (a) θ = 0 ° and (b) θ = 90 ° . Figs 5(a) and 5(b) show three average F – w relationships obtained with the splitting tensile test for specimens from the θ = 0º and 90 ° series, respectively. The “Average” curve was obtained by averaging the readouts of the five LVDTs Flow direction Notch direction Flow direction Notch direction Flow direction Notch direction Flow direction Notch direction