Valorization of dune sand in cement mortars: From fine aggregate to supplementary cementitious material

This study evaluates the dual role of dune sand (DS), used both as a fine aggregate and, after mechanical activation by grinding, as a supplementary cementitious material (SCM) in cement mortars.The experimental program involved the preparation of mortars with raw DS at various replacement levels of crushed sand (0–30 %) and the production of ground dune sand (GDS) by ball milling with different ball-to-sand ratios (7, 10, 12) for partial cement replacement (10–30 %). Before incorporation, GDS reactivity was assessed using laser granulometry, X-ray diffraction (XRD), the Chapelle test, and scanning electron microscopy (SEM). The workability, physical and mechanical properties and microstructural characteristics of the mortars were then evaluated. At a 30 % replacement level, the incorporation of raw DS improved both the density and compactness of the mortars, leading to enhanced mechanical performance compared to the control mix. Similarly, GDS, produced by ball milling with different ball-to-sand ratios, showed significantly increased fineness and reactivity, confirming its partial pozzolanic activation through XRD, FTIR and TGA analyses. The intermediate ball-to-sand ratio provided the most effective activation, promoting additional C–S–H formation while limiting particle agglomeration. At moderate cement replacement levels, GDS improved the mechanical properties due to the combined effects of pozzolanic reactions and filler-induced densification, whereas higher substitution levels resulted in reduced strength attributed to the clinker dilution. In conclusion, the study results demonstrated that DS and GDS can represent sustainable alternatives to natural sand and cement, enabling the formulation of high-performance mortars while contributing to resource preservation and reducing environmental impact. • Dune sand (DS) is an alternative to the use of common sand. • Replacing 30 % of crushed sand with DS improved workability, density, and mechanical strength. • Ground dune sand (GDS) is a pozzolanic additive. • Grinding of dune sand (ball/sand = 10) promoted partial amorphization of quartz and pozzolanic reactivity. • Optimal GDS addition (10 % cement replacement) enhanced compressive strength up to 58 MPa.