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CONCRETE TECHNOLOGY34 CPI %u2013 Concrete Plant International %u2013 3 | 2025 www.cpi-worldwide.comManufactured sand usage is increasing in concrete as resources of natural, fine aggregate become scarcer. Modern processing of these manufactured sands has the potential to reduce the need for blending with natural sands that are often extracted from sensitive environments. Typically, older technology use impact crushers that produce poorly shaped particles and washing is done to remove excess fines. Modern processing using vertical shaft impact (VSI) crushers and air screening can produce better quality manufactured sand, sometimes referred to as engineered or modern processed sand. These materials consistently have better grading and particle shape and less problematic ultra-fine particles.This article reviews a range of manufactured sands to compare the benefit of these different materials in concrete production. The performance is compared with concrete made with natural sands that are still available in some areas. Natural sand composed of rounded, hard particles produce high quality concrete with good cementitious efficiency and this was the reference to compare with manufactured materials.Sand quality assessmentSeveral factors affect the quality of aggregate blends used in concrete, which in turn influences the efficiency of cementitious materials:%u2022 Grading is well understood as it forms the matrix of particles from microns to millimetres in concrete (assessment usually done by sieve analysis)%u2022 Particle shape is important but is rarely measured despite the availability of several traditional and new techniques%u2022 Cleanness of material must be controlled since ultra-fines such as silts and clays can have a deleterious effect on concrete properties%u2022 Consistency of supply is also critical such that full-scale production can be reliably guaranteed without needing frequent control testing and post-hoc adjustmentsFigure 1 shows how optimum properties of fine aggregates are assessed in practice using either traditional techniques or modern alternatives.Modern processing of manufactured sand for concreteInfluence of fine aggregates on concrete propertiesn James Mackechnie, Allied Concrete, Christchurch, New Zealand Fig. 1: Optimum properties for fine aggregate blends in concrete.Silt contentSand equivalentClay index testingAdsorption/MBVDigital image analysisNZ sand flow testingMortar testingSieve analysis & finesses modulusParticle size image analysisBlending requiredBlending requiredCoarse gradingWell-graded sandFlaky shapeRounded or cubicalAngular shapeLacking finesNo deleterious finesExcessive finesGRADINGCLEANLINESSPARTICLE SHAPEGap graded or single sizedBlending requiredOptimum zone