studied the replacement of NS by 50 and 100% of UFS. However, at 28 days, the compressive strength of the mortars decreased compared to the control mortar. Compressive strength results at 3 days showed an increase of 13 and 12% when 15 and 30% of UFS were used, respectively. manufactured mortars with up to 60% replacement (in steps of 15%) of NS by UFS and a fixed W/C ratio of 0.5. This was attributed to the reaction of cement with aluminium, which produces hydrogen gas that creates microcracks in the cementitious matrix. The compressive strength results at 7, 14 and 28 days reported that the total inclusion of UFS decreased the compressive strength by 71, 77 and 76% compared to the control mortar. used UFS from an aluminium foundry as a total replacement for NS in the manufacture of mortars. However, with up to 10% replacement of UFS the compressive strength of the mortar was not affected significantly. At 28 days, the compressive strength of the mortars decreased when the replacement was higher than 20%, which was attributed to the presence of fine powder carbon and clay within the binder, causing a loosening of contacts and links between the aggregates and cement matrix. Monosi, Sani and Tittarelli used a replacement of up to 30% of natural sand (NS) by UFS with a fixed W/C ratio of 0.5, reporting a decrease in the workability of 8, 19 and 22% as the UFS content increased by 10, 20 and 30%, respectively. Regarding mortars, diverse authors have experimented with UFS and additions such as ceramic mould shells and paraffin waxes wastes, polyurethane residues, high phenolic contents and geopolymers. By means of vacuum belts, a magnet collects the metal debris, and the sand is used several times again in the manufacture of moulds until its properties are no longer suitable for the casting process, creating a by-product known as used foundry sand (UFS). Once the metal has cooled, the sand box is broken up by the “shakeout” method. The GFS or CFS is compacted against a mould that leaves a cavity in the shape of the part required, and then molten metal is poured into it. When chemical binders are used instead, such as phenolic-urethanes, epoxy resins, or sodium silicates, the FS is called chemical foundry sand (CFS). When organic binders such as bentonite clays are used along with carbon powder to enhance the cast surface, the FS is called green foundry sand (GFS). The main constituents of FS are silica sand and binders, which can be of natural or chemical origin. The authors recommend that for replacements higher than 25 wt.% of UFS, the W/C ratio has to be taken into consideration to obtain the same workability as the control mortar, although this decreases the mechanical properties.įoundry sand (FS) is the material used in the manufacturing of mould boxes in the sand-casting process of ferrous and nonferrous materials. Therefore, while small replacement levels lead to a slight improvement in the mechanical properties, this trend breaks down for high replacement levels due to the negative effect of the high W/C ratios required. From the results obtained, it is possible to conclude that the mortars with UFS require a higher amount of water. In terms of mechanical durability, the mortars with UFS showed abrasion marks within the limits of the EN-1338 standard. Flexural and compressive strength decreased when the replacement percentage was higher than 25 wt.%. For the physical properties of the mortars, density decreased and porosity and absorption increased at all replacement percentages. The incorporation of UFS decreases the workability of the mortars due to the absorption of the residue. The combined effect was evaluated of the W/C ratio and the replacement ratio on the workability, physical properties, mechanical properties, mechanical durability, and microstructure of the mortars. This study evaluated a total of 32 different mixes combining different W/C ratios varying between 0.5 and 0.7 with 5 replacement ratios of natural sand by UFS: 0, 25, 50, 75 and 100%, respectively. Since the presence of UFS will mainly affect the mortar that binds the aggregates in the manufacture of concrete, it was decided to isolate this fraction and study only the effect of UFS in mortars. Here, the recovery of UFS as fine aggregates for the manufacture of concrete is proposed. Virtually all UFS is currently landfilled, despite the economic and environmental cost overruns that this entails. Modern society requires a large number of metal components manufactured by sand casting, which involves the generation of a waste product known as Used Foundry Sand (UFS), of which approximately 100 Mt are generated on an annual basis.
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