# The Properties and Durability of Self-Leveling and Thixotropic Mortars with Recycled Sand
## 2 Materials and Methods
### Methods  
Thixotropic and self-leveling mortars, with natural and recycled aggregates, were produced using a water/cement ratio equal to 0.52 and a sand/binder ratio equal to 2.28. Two chemical kits, especially those designed for producing self-leveling and thixotropic mortars, were provided by Personal Factory s.p.a. and used in the experimental campaign. The chemical kit was equal to the 5 wt% of the overall admixture. In Figure 6, the mix design of the four types of mortars is reported. The mixing protocol establishes that water and cement are initially blended for 30 s. The chemical compound is then added and a further 30 s of blending is carried out. Natural or recycled sand is then added in 30 s under mixing, followed by 1 more minute of mixing time. The admixture rests for 1 min and 30 s and, finally, it is mixed again for 1 min before starting the tests. For each type of mortar, the nomenclature used is classified as follows: the first two letters correspond to the origin of the aggregate, i.e., natural aggregate (NS) or recycled aggregate (RS); the last two letters refer to the type of mortar, i.e., thixotropic (RX) and self-leveling (PX). At zero time after mixing, the workability of freshly prepared mortars was evaluated using the flow table and according to EN 1015-3 [69]. Several specimens, with a dimension of 40 mm \(\times\) 40 mm \(\times\) 160 mm, were produced according to EN 1015-11:2001 [70] and stored in a climatic chamber at 20 \(\pm\) 3 \({}^{\circ}\)C and RH 90 \(\pm\) 3% for certain cure ages. Compressive and flexural strengths, drying shrinkage, and open and total porosities were measured, according to relevant standard reported in Table 3. The drying shrinkage was measured on specimens stored in a dry environment (20 \({}^{\circ}\)C, RH 60%). Figure 5: The grain size distribution curve of the natural and recycled aggregate. The resistance of the prepared mortars to freeze-thaw cycles was tested according to the relevant standard reported in Table 3, after a curing period of 28 days. Saturated specimens were placed in the freeze-thaw cycle test machine under the condition of freezing temperature of \(-20\)\({}^{\circ}\)C and thawing temperature of 5 \({}^{\circ}\)C. Each cycle consisted of:  
1. a cooling phase, in which the temperature moved from 5 \({}^{\circ}\)C (\(\pm 2\)\({}^{\circ}\)C) to \(-20\)\({}^{\circ}\)C (\(\pm 2\)\({}^{\circ}\)C) at a constant rate of 5 \({}^{\circ}\)C/h (\(\pm 0.5\)\({}^{\circ}\)C/h);
2. a constant phase in which the temperature was kept constant at \(-20\)\({}^{\circ}\)C (\(\pm 2\)\({}^{\circ}\)C) for two hours;
3. a heating phase in which the temperature returns to 5 \({}^{\circ}\)C (\(\pm 2\)\({}^{\circ}\)C) at the same velocity as step. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Cement** & **Natural Sand** & **Recycled Sand** & **Water** & **Chemical Kit** \\  & **[kg]** & **[kg]** & **[kg]** & **[kg]** & **[kg]** \\ \hline NSRX & 539.3 & 1227.3 & - & 279.0 & 93 \\ RSRX & 496.0 & - & 1128.7 & 256.6 & 85.5 \\ NRPX & 539.3 & 1227.3 & - & 279.0 & 93 \\ RSRX & 496.0 & - & 1128.7 & 256.6 & 85.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The mixture proportions of mortars (kg/m\({}^{3}\)). Figure 6: The mix design of thixotropic and self-leveling mortars.