Issue 49

L. Restuccia, Frattura ed Integrità Strutturale, 49 (2019) 676-689; DOI: 10.3221/IGF-ESIS.49.61 685 impurities, reducing the higher absorption rate of recycled sand that influences workability of fresh state and mechanical properties of hardened state [30]. The second observation is that decreasing the amount of superplasticizer (Series 2), the results undergo a decrease for all the percentages. In fact, with the SP1 percentage of 0.75% there is a great decrease in terms of mechanical results between the Series 1 and the Series 2: this indicates that, fixed the w/c ratio, the correct amount of superplasticizer to use is equal to 1%. The drop both in mechanical and fracture parameters can be related to the lack of cement grain and recycled washed sand dispersion because of the fewer amount of SP1. By the Series 3 analysis, it is not surprising to find an improvement for all the compositions: the superplasticizer was brought back to optimum condition (1%) and the w/c ratio has been decreased (from 0.50 to 0.45), which have great influence on workability and hardened properties of mortars [31]. In Figs. 9-11 are reported the Load-CMOD curves, obtained by TPB tests for mortars with SS and mortars with RSw, for each series considered. From the observation of experimental curves, it is possible to note that mortars with recycled sand percentage replacement above 75% behave in a "more ductile" manner with respect to the standard mortar. This can be attributed to the presence of the superplasticizer, which counterbalances the detrimental effects associated with the use of recycled sand in compositions. As found in literature, if superplasticizer is used to reduce the w/c ratio, the fine recycled fraction can be as good as the conventional type [32]. For this reason, in Series 3 (w/c = 0.45; 1.00 % SP1), the best results can be found. Moreover, the improvement in ductility at 75% RSw might be linked to the increase in elongated grains of recycled sand replacing the more spherical standard sand grains in cementitious matrix. Figure 9: Load-CMOD curves, series 1. Figure 10: Load-CMOD curves, series 2.