Dune Sand Substitution and Superplasticiser Type as Co-Determinants of Fresh and Hardened Concrete Performance: A Study Using Local Algerian Materials

<ns7:p> The availability of locally sourced, low-cost aggregates for concrete production is a critical issue in arid regions of North Africa, where access to conventional materials is often limited, and construction costs are high. This study investigates the combined effects of dune sand substitution and superplasticiser on the performance of both fresh and hardened concrete, using locally sourced Algerian materials. Dune sand was gradually replaced with crushed limestone sand at six levels (0 to 60%), alongside two commercially available superplasticisers: an acrylic copolymer (rheology-modifying) and a polycarboxylate (workability-modifying). All mixes were prepared with CEMII/A42.5 cement at a constant water-to-cement ratio of 0.5. Fresh concrete properties were evaluated through penetration (workability) and fresh density tests. Hardened concrete was characterised by compressive strength, dynamic Young’s modulus, and dynamic Poisson’s ratio. The acrylic copolymer superplasticiser demonstrated significantly improved workability at all substitution levels (34 to 70 mm), with optimal fresh-state performance at 40% and 50% dune sand substitution, and a fresh density consistently above 2.3 t/m <ns7:sup>3</ns7:sup> . The polycarboxylate admixture reached its optimum at lower substitution rates (10 to 30%), with a slightly workable range (32 to 34 mm). Both Admixtures produced mechanically robust hardened concrete, attaining compressive strengths up to 48 MPa. Acrylic copolymer mixtures are more stable indicators, with improved matrix homogeneity. Dune sand from the Béchar region can be used as a partial aggregate replacement in structural concrete up to 50% by mass when the appropriate superplasticiser is employed. Superplasticiser type and aggregate are key factors influencing concrete performance: the acrylic copolymer is generally compatible with dune sand and is recommended at 40–50% substitution for optimal fresh-state performance; meanwhile, the polycarboxylate admixture is suited for 10–30% substitution when compressive strength is a priority. These findings provide directly applicable, evidence-based guidance for the valorisation of dune sand in sustainable, cost-effective construction. </ns7:p>