# The Properties and Durability of Self-Leveling and Thixotropic Mortars with Recycled Sand
## 2 Materials and Methods  
### Materials  
Cement of type CEM II/A-LL 42.5 R was used to manufacture mortars. This was produced in accordance with standard UNI EN 197-1. The cement particle size distribution, based on volume distribution, is: D50 = 19.84 um; D90 = 36.11 um; D10 = 8.414 um. Its main components, in terms of oxides were SiO\({}_{2}\) = 18.61 wt%; Fe\({}_{2}\)O\({}_{3}\) = 2.87 wt%; Al\({}_{2}\)O\({}_{3}\) = 4.38 wt%; CaO = 60.60 wt%; MgO = 3.16 wt%; K\({}_{2}\)O = 0.79 wt%; Na\({}_{2}\)O = 0.35; MnO = 0.17 wt%; SO\({}_{3}\) = 2.83 wt%; TiO\({}_{2}\) = 0.2 wt%. A natural siliceous sand was used in the experimental campaign to produce the control mortars. The recycled aggregate came from the demolition of a building used as a warehouse. The demolition waste was then sorted by obtaining approximately 60 m\({}^{3}\), mainly consisting of bricks, lime and cementitious mortars, and concrete. High-quality aggregates were then produced by dry grinding and sieving. Scanning electron microscopy energy-dispersive X-ray analysis was used to investigate the morphology and elemental composition of the sands. Analyses were carried out with the help of a computer-controlled field emission Phenom ProX, equipped with an energy-dispersive X-ray (EDX) spectrometer (Deben, Suffolk, UK). Before SEM observation, the samples were sputtered with gold to stop their non-conductive surfaces from changing, and images were acquired at 20 kV. The counting time for the EDX analysis was 120 s.  
Shape, surface texture, and mineralogical composition of sands can markedly affect the fresh and hardened state properties of the produced mortars and their durability [53; 54; 55]. In Figure 1, the SEM analysis of recycled aggregate (RS) and natural sand (NS) are reported. Natural sand (Figure 1B) is characterized by angular and rough grains. Recycled sand contains grains with irregular shape and sharply cut edges and some of grains show cracks throughout their microstructure (Figures 1A and 2). Their formation is promoted by the crushing process at the interfacial transition zone (ITZ) of concretes and mortars used as starting materials to produce RS, as reported by other authors [56; 57]. Figure 1: SEM analysis of recycled sand (**A**) and natural sand (**B**). Natural sand is mainly composed by a silica, with other elements indicating the presence impurities (Table 1). The main elements found in the recycled aggregates (Table 1) are silicon, calcium, aluminium, and iron, originating from cementitious compounds (concretes and mortars) and bricks. In Figure 2, the EDX mapping analysis of recycled sand is reported, revealing the heterogeneity of composition among grains. Automated morphological imaging was carried out using Morphologi-G3 (MALVERN). This was used to investigate the recycled particles' shape; the circle equivalent (CE) diameter, defined as the diameter of a circle with the same area as the 2D image of the particle [58]; and the high sensitivity circularity (HS circularity) defined as:  
\[\text{HS circularity}=4\pi\text{A}/\text{P}^{2}\]  
where A is the particle area and P is its perimeter [58]. HS circularity has values in the range 0-1. A perfect circle has a circularity of 1, while a'spiky' or irregular object has a circularity value closer to 0. Representative results are reported in Figure 3.  
The calculated HS circularity for RS, based on the analysis of more than 500,000 particles was 0.8. Recycled sand was analyzed by X-Ray diffractometry using a Rigaku MiniFlex 600 X-ray diffractometer (Rigaku Corporation, Tokyo, Japan) with CuK\(\alpha\) (wavelength of 1.5406 A) radiation generated at 20 mA and 40 KV. This was scanned at 0.02 20 step at a rate of 1\({}^{\circ}\)/min between 5\({}^{\circ}\)and 50\({}^{\circ}\) (20 angle range). The obtained X-Ray diffraction pattern is shown in Figure 4.