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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1. Introduction

As is well-known, mortar (as well as all cementitious materials) exhibits high compressive strength, but low tensile strength and fracture toughness. In order to achieve higher values of both tensile strength and fracture toughness, different synthetic fibres have increasingly been used as a reinforcement for mortar during last decades (Sharma et al., 2013). The main drawbacks of synthetic fibres are the high costs and the large amount of energy dissipation in the production process. Therefore, natural fibres (such as flax, jute, sisal, coir and bamboo fibres) are an attractive field for many researchers due to their desirable characteristics, represented by availability, renewability, low density and costs (Ardanuy et al., 2015). Several investigations have been carried out (Kriker et al., 2005; Alzebdeh et al., 2016) in order to characterize date-palm fibre-reinforced mortar and take advantage of its peculiar properties, such as the ductile behaviour, in applications where high strength is not the main design requirement. In the present paper, the fracture behaviour of a cement-based mortar reinforced with short vegetable fibres is examined. Such fibres are extracted from the Date Palm Mesh (DPM), which is the fibrous structure surrounding the trunk of the date palm. In particular, three-point bending tests are carried out on single edge-notched specimens of both plain mortar and mortar reinforced by five different values of date-palm fibre percentages (2, 4, 6, 8 and 10% by volume). The Modified Two-Parameter Model, MTPM (Jenq and Shah, 1985; Scorza et al. 2015; Carpinteri et al., 2015a-b, 2017a-b; Spagnoli et al., 2016; Vantadori et al., 2016a-b, 2018; Bernardi et al., 2017), is applied to compute the fracture toughness, taking into account the possible kinked crack occurring during the stable crack propagation. The DPM fibres in the present study are obtained from Deglet-Noor date palms (which is one of the most appreciated variety in the world) from the oasis of Tolga (Biskra, Algeria). Single fibres are manually obtained from DPM sheets and washed with fresh water. Then, such fibres are dried at room temperature for one week and cut to 7-10 mm in length (Fig. 1). Since such fibres have the same geographical origin as those used in the experimental campaign by Kriker et al. (2005), it is reasonable to assume that the present fibres are characterised by similar physical properties (Table 1). The cement-based mortar matrix consists of a limestone Portland cement (42.5 CEM II/A-LL type) and a silica sand, with a grain size distribution according to the UNI EN 196-1:2005 European Recommendation. For the specimen casting, the mixture proportions are cement:water:sand (by weight) = 1:0.55:3. The ratio between water and cement is fixed after performing a workability test by using a flow table, according to the UNI EN 1015-3:2007 European Recommendation. 2. Experimental campaign 2.1. Specimens casting

Fig. 1. DPM fibres: single fibres dried and cut (7-10 mm).