PSI - Issue 13

Andrea Zanichelli et al. / Procedia Structural Integrity 13 (2018) 542–547 Zanichelli et al./ Structural Integrity Procedia 00 (2018) 000 – 000

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Such a model is able to take into account the possible crack deflection during the stable crack propagation. As is experimentally observed, cracks may deflect during the propagation stage even under remote pure Mode I loading. Such a deflection is the result of the shear stress produced by both inhomogeneities embedded in the cementitious matrix and slippage at the interface between cementitious matrix and fibres. Note that fracture toughness would be overestimated by considering crack propagation under pure Mode I loading. 3. Results and discussion The results deduced by employing the MTPM are listed in Table 2. The averaged values of peak load max P , elastic modulus E , and critical mixed mode SIF S I II C K ) (  are displayed in such a Table. In agreement with the results by Coutts and Warden (1992) and Savastano et al. (2003), both elastic modulus and fracture toughness decrease by increasing of the date-palm fibre content (Table 2). This behaviour is related to both the lower elastic modulus of the vegetable fibres with respect to the matrix elastic modulus and the incorporation of air during the mixing phase, which increases with the amount of fibres. Figure 3 shows the load – CMOD curves for both plain mortar and mortar reinforced with 8% of date-palm fibres. A significant load-bearing capability increasing in the post-peak behaviour can be noticed, even in the case of large values of CMOD. More precisely, the averaged peak load for RM8 is around 50% of that for PM specimens type. Both RM8 and PM specimens show a similar value of load in correspondence to a CMOD = 0.1mm. For greater values of CMOD, the load for PM specimens tends towards zero, whereas that for RM8 maintains a near constant averaged value (for instance, in the case of CMOD = 0.2mm, the averaged load for RM8 is around 5 times greater than that for PM specimens type). Following an approach similar to that reported in the papers by Gopalaratnam et al. (1995) and Jamet et al. (1995), a toughness index based on the measure of the area under the experimental load-CMOD curve is hereafter proposed in order to better understand the effect of fibre volume fraction on the fracture behaviour of the cement-based mortar. More precisely, the area under the load-CMOD curve can directly be correlated to the material ductility.

Table 2. Averaged values of peak load, elastic modulus and critical mixed mode SIF. Specimen type max P [kN] E [MPa] S I II C K ) (  [MPa(m) 0.5 ] PM 0.237 23593.938 0.672 RM2 0.227 17007.701 0.598 RM4 0.196 15054.946 0.555 RM6 0.128 11616.002 0.383 RM8 0.111 7292.006 0.285 RM10 0.095 3711.868 0.218

0.3

0.30

(a)

Reinforced mortar - RM8 (b)

Plain mortar - PM

0.2

0.20

0.1 LOAD, P [kN]

0.10

0.0

0.00

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.3

CMOD, [mm]

CMOD, [mm]

Fig. 3. Typical load – CMOD curves for: (a) plain mortar specimens; (b) reinforced mortar specimens with date-palm fibre content equal to 8%.