Issue 49

L. Restuccia, Frattura ed Integrità Strutturale, 49 (2019) 676-689; DOI: 10.3221/IGF-ESIS.49.61 687 In Fig. 12, the curve Load-CMOD for two experimental specimens of the Series 4 is shown, through which it is possible to explain the enhancement of fracture energy, by evaluating the ductility factor μ. Ductility factor is defined as the ratio between the ultimate displacement δ u and displacement corresponding to the peak load δ P :  μ δu / δP  (6) and, in this case, it is equal to 1.92 for M-SS (Specimen#2) and 2.47 for M-RSw_100% (Specimen#2). Analysing the values of Young’s modulus E reported in Tab. 9 and observing Fig. 12, a little change of slope of the first portion of the Load- CMOD curves can be seen. In literature, the lowest Young's modulus is attributed to the residues adhered of recycled aggregates [33], but probably in this case there is still a correlation with the amount of superplasticizer used. In fact, in the traditional mortar 4.5 g of SP1 have been used while 13.5 g in the mortar with 100%RSw (as reported in Tab. 3). This lead to a difference in density of the two mixtures, which may explain the small decrease in the elastic modulus, according to Mehta and Monteiro [34]. C ONCLUSIONS n this research work, an investigation regarding the feasibility of replacing in traditional mortars the fine fraction of CDW waste has been conducted. This topic has still little relevance in scientific literature, as it is believed that the greater water absorption of recycled sand could compromise mechanical properties of both fresh and hardened states. The importance of this research lies in the fact that, through the washing process, it is possible to obtain suitable sand to be re-used in building materials. Mechanical and fracture properties of mortars with RSw are extremely similar to those of traditional mortars, even exhibiting an improvement regarding fracture toughness and fracture energy. Based on the test results, the main conclusions are as follows:  the higher the percentage of Recycled washed sand in mortars, the higher mechanical performances. This is probably related to a huge presence of irregular and indented grains of recycled sand, which ensure a more cohesive bond with cement matrix;  the presence of the superplasticizer counterbalances the detrimental effects associated with the use of recycled sand. Their joint use is a solution to offset the negative effects caused by recycled sand incorporation [19] and, if superplasticizer has being varied with respect to the weight of recycled sand for each composition, then the workability is ensured; this is a critical parameter for the performance of fresh and hardened states;  it is possible to evaluate not only the fineness of the recycled sand used in correlation with water requirement, but also the quality of the superplasticizer as parameters for the mix-design of the mixture [19-21].  although specific studies are required in order to obtain an optimal mix-design of mortars made with fine recycled sand, it can be stated that it is technically feasible to use it for mortar production, especially when powder of < 0.08 mm fraction is eliminated. A BBREVIATIONS SS , standard sand; RS , recycled sand; SP , superplasticizer; RSw , recycled washed sand, CDW , construction and demolition waste; M-SS , mortar with standard sand; M-RSw , mortar with recycled washed sand; ITZ , Interfacial Transition Zone. R EFERENCES [1] Steinberger, J.K., Krausmann, F. and Eisenmenger, N. (2010). Global patterns of materials use: a socioeconomic and geophysical analysis, Ecological Economics 69, pp. 1148-1158. DOI: 10.1016/j.ecolecon.2009.12.009. I