Three-dimensional characterization of morphology and abrasion decay laws for coarse aggregates

In order to quantitatively evaluate morphological characteristics and abrasion decay laws of coarse aggregate so that make an accurate performance evaluation for aggregates, flat-elongated index, sphericity index and specific surface area are proposed to characterize the shape properties of coarse aggregate. Limestone aggregate particles ranging in size scale of 4.75-9.5 mm, 9.5-13.2 mm, 19-26.5 mm were worn by the Los Angeles Abrasion tester respectively. Three-dimensional (3-D) laser scanner was used to obtain three-dimensional points cloud data of aggregate particles experienced 0, 500, 1000 and 2000 abrasion cycles. Afterwards, the data was processed by the software of reverse engineering based on morphology evaluation indexes, and the minimum bounding box algorithm was developed to calculate flat-elongated index, illustrating the morphological characteristics of coarse aggregate particles with different size and abrasion cycles. Test results show that: aggregates with small size have bigger quantity proportion of elongated particle; the greater the angularity of aggregates was, the faster the angular decay rate of the aggregates was; aggregate particles with small size has richer surface texture but easier to lost in abrasion process. Sphericity index increased, while specific surface area and flat-elongated index presented a downward trend as the particle size became bigger for different abrasion cycles. However, the flat-elongated index of aggregate particles with different size increased abnormally when abrasion cycles increased at 2000 abrasion cycles as the result of aggregate crushing. Besides, the sphericity and specific surface area of some 4.75 mm aggregate under 500 abrasion cycles showed an abnormal increasing compared to its 1000 abrasion cycles, which caused by inadequate abrasion under low abrasion cycles. Therefore, the indexes proposed in the study are able to characterize different aspects of coarse aggregates morphological property, and it is beneficial for the evaluation and selection of aggregates used in engineering construction.