PSI - Issue 13

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

546

5

3

0 20 TOUGHNESS INDEX, I t [-] 0 5 PM RM2 RM4 5 10 15

(b)

(a)

RM6 RM8 RM10

PI P PI K PI T

2.5

2

1.5

1

0.5 PERFORMANCE INDICES [-]

0

10

15

0 2 4 6 8 10 FIBRE CONTENT, n [%]

MULTIPLIER, m  [-]

Fig. 4. Averaged values of: (a) toughness index for each specimen type as a function of the multiplier m of the CMOD peak ; (b) normalized Performance Indices related to peak load, PI P , fracture toughness, PI K , and toughness index, PI T , against the fibre content.

Such a toughness index t I is here defined as the ratio between the area under the load-CMOD curve up to a prescribed multiple,  m CMOD peak , of the CMOD at the peak load and the area under the same curve up to CMOD peak . In particular, the toughness index is computed for all the tested specimens by considering five different multipliers of the CMOD peak value, that is,  m 1, 3, 5, 10, 15. The averaged toughness index for each specimen type is reported in Fig. 4(a) as a function of the multiplier m of the CMOD peak . It can be remarked that, for  m 3, the toughness index presents a similar value for each specimen type. For m values greater than 3, it can be observed that the larger is the fibre volume fraction, the greater is the value of t I , especially in the case of high values of m . Such an effect is due to date-palm fibre effectiveness at large deformations. It is worth noting that the weight of the reinforced specimens is slightly lower than that of the plain specimens. In particular, the higher is the fibre content, the lighter is the specimen. In order to correlate the specimen density to the mortar mechanical parameters, three different Performance Indices are hereafter examined: PI P , PI K , and PI T , related to the peak load max P , the fracture toughness S I II C K ) (  , and the toughness index t I , respectively. Each of such indices is defined as the ratio between the correspondent mechanical parameter and the specimen density (equal to 2,656kg/m 3 for PM specimens, and to 2,470kg/m 3 for RM10 specimens). The averaged values of PI P , PI K and PI T , normalized with respect to plain mortar, are presented in Fig. 4(b), as a function of the fibre content. It can be remarked that, by increasing the fibre percentage, both PI P and PI K decrease, while an opposite trend is obtained for PI T . This means that the performance of cement-based mortar is improved in terms of material ductility when it is reinforced with date-palm fibres. An experimental research work has been carried out on the fracture properties of a cement-based mortar reinforced with date-palm fibres. In particular, three-point bending tests on notched specimens reinforced with date palm fibres have been performed by examining five different values of fibre content. It can be observed that an increase of the fibre content does not produce a positive effect on both peak load and fracture toughness, since the best performance in terms of such parameters is achieved when plain mortar specimens are used. This is mainly due to: (a) mechanical properties of the fibres lower than those of the mortar matrix; (b) air incorporated during the mixing phase, which increases by increasing the fibre content; (c) poor bonding at the fibre matrix interface. On the other hand, the addition of date-palm fibres in mortar specimens improves the ductility in comparison to that of plain specimens and delays the failure of the composite material. Although the increase of fibre content reduces both the peak load and the fracture toughness of reinforced mortar with respect to those of plain mortar, the greater energy absorption capability observed in the reinforced mortar specimens promotes the use of such a material in applications where (i) lightness and ductility are pursued and (ii) high strength is not the main design requirement, such as in non structural applications. 4. Conclusions