Issue 49

L. Restuccia, Frattura ed Integrità Strutturale, 49 (2019) 676-689; DOI: 10.3221/IGF-ESIS.49.61 677 the influence of either replacement percentage or replacement fraction of natural sand by recycled sand, by volume (slump, compressive and flexural strength, ITZ microstructure). The results showed that the slump of mortars containing dried recycled sand is always larger than the one of the mortars with saturated one (pre-saturated 24h before the mix), because water is not immediately adsorbed into the cement paste at the initial time [13]. Moreover, results also showed that the compressive strength of mortars with recycled sand is always lower than the reference mortar, with a quasi-linear decrease as the replacement percentage of recycled sand increases [13]. Two parameters to be taken into account for the realisation of construction materials with fine recycled sand are the amount of fine content, which influence its workability, water absorption and shrinkage [14-16] and the amount of superplasticizer, which prevents the flocculation of cement particles when recycled aggregates are used [17]. Miranda and Selmo [18] analysed the effect of materials finer than 75  m on mortar properties and they found that the distribution of the pore sizes generated by the presence of fines in the mixtures had a higher effect on drying shrinkage than those of the porosity introduced by the effective water/cement ratio itself. Bravo et al. [19] studied the superplasticizer efficiency on the mechanical properties of recycled aggregates concrete founding that incorporation of 1% of polycarboxylic-based superplasticizers has been beneficial in all percentages used, but the extent of its effect was dependent on the aggregate composition. Cartuxo et al. [20] studied the rheological behaviour of concrete made with fine recycled concrete aggregates founding that the addition of high-performance superplasticizers (a fixed proportion of 1% of cement mass was used) can offset the negative effects of fine recycled aggregates concrete introduction in mixtures. The fine fraction of CDW can be used like a filler to produce engineered cement composites [21] or for preparing self-compacting concrete mixes, but 20% is the maximum replacement level [22] while its use only as a replacement of standard sand is almost impossible. Therefore, the objective of this study is the utilisation of fine CDW (also called recycled sand) to reproduce the granulometric distribution of the standard one, to completely replace it in traditional mortar. The authors, in their first investigation about recycled sand in mortars [23], have analysed its effect in different compositions without additions of superplasticizer. As expected, the large water demand has been the main problem and it has not been possible to replace over 50% of standard sand. For this reason, superplasticizer has been used to obtain a workable mixture: it was added with respect to the weight of cement, nevertheless the problem of workability has not been resolved. On the contrary, the authors achieved quite satisfactory results through the recycled sand washing process, which allows the elimination of finer particles of poor quality, by using water and sieves, limiting the problem of water absorption [24]. Another important result obtained was related to the percentage of superplasticizer, added on the basis of the weight of the recycled sand (the quantity usually varies according to the weight of the cement): this solution was suitable to go beyond the complexity of the exact prediction of required w/c ratio for attaining the desirable mechanical performances. In this research paper, the prosecution of the previous research [24] has been carried out: the percentages of substitution reach up to 100% to promote the sustainable use of recycled sand into traditional mortars. Moreover, the recycled sand- based composites have been characterized not only from a mechanical point of view, but they were also analysed considering the fracture behaviour and the variation in the phase compositions via X-ray diffraction analysis. M ATERIAL AND METHODS Materials and specimen’s preparation n this work, recycled sand provided by Cavit S.p.A. has been used (Fig. 1). It is characterized by particle size less than 8mm, with a plasticity index and a liquid limit equal to 0.9 and 26.4 respectively (Atterberg Limits). In the Declaration of conformity of this product (CE Marking) drawn up by the Cavit S.p.A., according to UNI EN 13242:2013 - “Aggregates for unbound and hydraulically bound materials for use in civil engineering work and road construction”, the parameters are indicated in Tab. 1 below: Density of particle 2.5 Mg/m 3 Fine granular content Fine granular quality Water Absorption SE≥ 28 MB 1.25 4 ≤ WA 24 ≤ 6 Table 1 : “Recycled 0-8” (UNI EN 13242). I