Page 33 - Demo

CONCRETE TECHNOLOGYwww.cpi-worldwide.com CPI %u2013 Concrete Plant International %u2013 3 | 2025 33Experimental investigationFine aggregate sourcesThree types of fine aggregate were used in the laboratory assessment of mortar and concrete mixes:%u2022 Natural sand (NS) from an alluvial source that is typically well graded and shaped to be used without any blending with other fine aggregates%u2022 Two modern processed sands (MP) that are well graded below 4 mm, have cubical shape particles and do not need blending with a fine sand%u2022 Four manufactured sands (MS) that were coarsely graded from 6 mm down, have angular shape, in some cases contain deleterious fines and all required blending with fine dredged or dune sandsBlending of fine sand with manufactured sand was at 40-50 % to provide a continuous grading with fineness modulus of 2.7 to 2.8 (using ASTM sieves). Grading of natural sand and modern processed sand was slightly finer with fineness modulus between 2.5 and 2.7. When comparing the properties of the modern processed sand with manufactured sand two significant differences were seen (see also Table 1):%u2022 MS particles are more angular having sphericity and roundness values close to 0.50 whereas MP particles had values above 0.70 (MP sand also had lower flow times and voids when tested with the NZ sand flow test)%u2022 Cleanness of MP sand was better than MS, especially when air screening was used in the process (cleanness assessed using silt sedimentation test, sand equivalent and clay index testing)All aggregate was derived from greywacke sandstone that is the major geological source of rock in New Zealand. Relative density of material ranged from 2.62 to 2.68 with absorption n Dr James Mackechnie is responsible for readymix concrete quality control and assurance for Allied Concrete in New Zealand. He is also Adjunct Senior Researcher at the University of Canterbury where he has interests in concrete technology issue involving sustainability and durability. He has 35 years of experience working in construction, design and production of concrete structures both in New Zealand and South Africa.james.mackechnie@alliedconcrete.co.nzTable 1: Summary of fine aggregate materials in terms of overall quality indicators.Fine aggregatetype (notation)Grading (subjective rating)Particle shape Cleanness Concrete propertiesNatural sand (NS) Continuous, well graded Rounded to sub-roundedRelatively clean, washedLow water demandModern processed (MP)Well graded from 3 mm downCubical Excess fines removed* Moderate water demandsManufactured sand (MS)Coarse grading, requires blendingAngular Washed but some dirt Higher water demands*MP1 used washing to remove ultra-fines while MP2 used air screening1 RECEPTION HOPPER4 HOPPERS OF 70 MC / EACH FOR A TOTAL OF 280 MC8 HOPPERS OF 35 MC / EACH FOR A TOTAL OF 280 MC1 LOADING SYSTEM WITH BUCKET ELEVATOR FOR HOPPERS3 CEMENT SILOS OF 80 TON EACH2 PLANETARY MIXERS MPR SERY HIGH PERFORMANCE 3000/2000 LTMIXER AUTOMATIC WASHING SYSTEM1 AGGREGATE MOBILE WEIGHING BUCKET2 CEMENT SCALES2 WATER SCALES2 ADMIXTURE SCALESCONTROL PANEL IN PROTECTION CABINCAMERAS VIDEO CONTROL1 DIRTY WATER DOSER1 DIRTY WATER TREATMENT SYSTEMAUTOCLAVE WATER SYSTEM WITH STORAGE TANKEXCELLENCEIN CONCRETE BATCHING PLANTSTAILOR MADEBATCHING PLANTSTURNKEY SOLUTIONSwww.rocchipg.euCMYCMMYCY CMYKRocchi logo allargato.pdf 1 11/03/19 17:24PASSAGGIO DI BETTONA (PG) ITALYTOWER CONCRETE BATCHING PLANT TK TYPE FOR A HIGH PRODUCTION OF QUALITY CONCRETE FOR THE PRODUCTION OF PRECAST ELEMENTS