# The Properties and Durability of Self-Leveling and Thixotropic Mortars with Recycled Sand
## 4 Conclusions  
In this study, authors produced self-leveling and thixotropic mortars using 100%wt of recycled aggregate. Their physical and mechanical properties and their durability were investigated and compared with the control mortars. The following outcomes are stated below. * The use of pre-saturated RS prevented the absorption of free water during the mixing. The workability of RSRX and RSPX mortars was 6% and 12% lower than that of the control mixes, respectively. * The thixotropic and self-leveling mortars produced with recycled aggregate showed porosities of 35.6% and 32.6%, respectively. The higher porosity affected both their drying shrinkage behaviour and mechanical properties. In particular, RSRX mortars showed an increase of 23.1% in the drying shrinkage and a loss of about 40% in the compressive strength compared to the control mortar. RSPX mortar showed a loss of about 6% in the compressive strength and an increase of 13.5% in the drying shrinkage with respect to the control mix. The variation in properties was more pronounced in the thixotropic mortars, where the chemical additives contributed to the fast water consumption that partially hindered the wettability of adherent cement paste on recycled aggregate. * After 300 freeze-thaw (F-T) cycles, RSRX and RSPX mortars, respectively, lost 11.6% and 14% of their initial compressive strength. Their greater porosity favours the dissipation of hydraulic pressures, resulting in a freezing and thawing resistance that is comparable to that of the control mortars, which experienced a loss of strength of about 10%. * After a period of 6 months under sulphate attack, the self-leveling and thixotropic mortars with recycled aggregate showed a loss of compressive strength of about 55% and 62% respectively. Conversely, the decrease in the corresponding control mixes was 63% and 69%, respectively. The greater extent of porosity in RSRX and RSPX mortars, even favouring the ESA kinetics, reduces the internal restriction of mortar to deform and the generated internal stresses due to the formation of expansive products. * The decline in the mortars' compressive strength containing recycled aggregate, after exposure at high temperatures up to 700 \({}^{\circ}\)C, is about 55% for RSPX and 19% for RSRX. This is comparable to that of the control mixes. In the 100-400 \({}^{\circ}\)C temperature range, a significant decrease in UPV, equal to 28.9% for RSPX, 36.9% for NRPX, 30.8% for RSRX, and 37.1% for NRSX, is observed and can be attributed to the dehydration-dehydroxylation of calcium silicate hydrate. Furthermore, a steeper decrease in UPV was measured in the 20-100 \({}^{\circ}\)C interval for mortars with recycled aggregate. This can be explained by the greater ease of water vapour to escape in mortars that are more porous and of the fine-cracks to develop, under vapour pressure, from the original defect of the recycled aggregate at the pore boundaries. The present investigation shows that the use of high-quality and purity-recycled aggregates, obtained by selective demolition, can help to produce mortars with acceptable properties and durability, even when a high amount of natural sand is replaced. Authors believe that a further tuning of the additives types and amount, the pre-treatment of the recycled aggregate to reduce the ceiling effect, and the partial replacement of Portland cement with pozzolanic powders could further improve the performance of the investigated mortars. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Mixes** & \(\Delta\)**Weight (\%)** & \(\Delta\)**Compressive Strength (\%)** & \(\Delta\)**Flexural Strength (\%)** \\ \hline NSPX & \(-5.5\)\% & \(-49.9\)\% & \(-52.1\)\% \\ RSPX & \(-8.7\)\% & \(-61.5\)\% & \(-55.6\)\% \\ NSRX & \(-14.9\)\% & \(-21.8\)\% & \(-44.4\)\% \\ RSRX & \(-19.2\)\% & \(-19.0\)\% & \(-40.7\)\% \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Variations in the weight and mechanical properties after thermal cycles. **Author Contributions:** Conceptualization, S.C., F.T. and F.C. ; Data curation, S.C. and F.T.