Numerical characterization of the geometric shape of coral sand by particle shaping and study on the properties of graded composite coral fine aggregate

High porosity and complex morphological characteristics of coral coarse aggregates typically lead to low strength, poor durability, and significant variability in coral concrete properties. This study examined the diverse properties of coral sand produced by jaw crushing and mechanical ball milling respectively. The geometric characteristics of the coral sand were quantitatively analyzed, and the effects of two processing methods on the morphology and porosity of coral sand were explored. Coral sands produced by each method were combined into coral fine aggregates with varying gradations, and the intrinsic relationship between the characteristics of coral fine aggregate and its concrete properties and porosity was explored. The results demonstrated that jaw crushing or ball milling significantly improved particle morphology and reduced porosity of the coral aggregates. Jaw crushing coral sand predominantly exhibited transverse fractures, while mechanical ball milling coral sand often exhibited longitudinal fractures. Under equivalent grading conditions, ball-milled coral sand achieved higher packing density and apparent density, alongside lower void ratios and water absorption rates. The study further demonstrated that the porosity, morphology, and gradation of the fine aggregates are crucial determinants of coral concrete's performance. B-II_2.7 coral fine aggregate was tightly packed and the morphology of coral sand was good. The fluidity and 7-day compressive strength of CB-II_2.7 had increased by 24.2 % and 27.7 % respectively compared to these of CJ-I_3.4, and its porosity had decreased by 29.8 %. 

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