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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Table 1. Physical properties of DPM fibres according to Kriker et al. (2005). Property Range Bulk density [kg/m 3 ] 512.2-1088.8 Absolute density [kg/m 3 ] 1300.0-1450.0 Natural moisture content [%] 9.5-10.5 Water absorption after 5 min under water [%] 60.1-84.1 Water absorption to saturation [%] 96.8-202.6

The date-palm fibres are submerged in water at room temperature for 24 hours and then dried in air, before being added to the mixture. This operation is needed to avoid that fibres absorb an excessive amount of mixing water during the casting. Subsequently, the DPM fibres are added in the cement-based mortar matrix, with five different fibre contents, equal to 2, 4, 6, 8 and 10% by volume. Then a superplasticizer (named Concretan200l, produced by Ruredil), with a content of 1% of cement weight, is added to the mixture to achieve the desired self-compacting properties. The reinforced mortar specimens are called RM n , where n is the fibre percentage being examined (i.e. n = 2, 4, 6, 8 and 10), whereas the plain cement-based mortar specimens are named with the acronym PM in the following. Therefore, six different types of specimens are examined. Three-point bending tests on notched specimens are carried out after 28 days of curing by means of the universal testing machine Instron 8862 (available at the “Testing Laboratory of Materials and Structur es ” of the University of Parma). Such tests are performed according to the TPM proposed by Jenq and Shah (1985), the RILEM Recommendations 50-FMC (1985), and 89-FMT (1990). The tested specimens present a notch in the lower part of the middle cross-section, and are characterised by the following geometrical sizes (Fig. 2): specimen depth-width ratio = W B = 2; support span-specimen depth ratio = S W = 4; notch length-specimen depth ratio = a W 0 = 1/3, and notch width smaller than about 3mm. In more detail, each specimen consists of a beam 15mm x 30mm x 160mm ( B W L   ), S = 120mm, and the notch length 0 a is equal to about 10mm (Fig. 2). The tests are performed under Crack Mouth Opening Displacement (CMOD) control, with an average rate equal to 0.1 mmh -1 . Moreover, the applied load is measured by means of a load cell. Each specimen is monotonically loaded. After the peak load max P is achieved, the post-peak stage follows and, when the load is equal to about 95% of max P , the specimen is fully unloaded (up to a load value equal to about zero) by proceeding under load control. Finally, the specimen is reloaded up to failure under CMOD control with the same initial average rate. On the basis of the experimental results in terms of peak load max P , the Modified Two-Parameter Model (MTPM) allows us to compute initial ( i C ) and unloading ( u C ) linear elastic compliances, elastic modulus E , and fracture toughness S I II C K ) (  , as was detailed by Vantadori et al. (2016b, 2018) and Carpinteri et al. (2017a-b). 2.2. Testing procedure

P

W = 30

a 0 = 10

B = 15

S = 120

L = 160

Fig. 2. Geometric sizes and loading configuration for three-point bending tests on notched mortar specimens (sizes in mm).