The morphological characteristics of brick-concrete recycled coarse aggregate based on the digital image processing technique

Recycled coarse aggregates, including crushed brick recycled coarse aggregate (CBRCA) and crushed concrete recycled coarse aggregate (CCRCA), are increasingly used as raw material in building materials. In fact, the morphological characteristics of recycled coarse aggregates take great effect on properties of materials. Therefore, this paper mainly investigates the morphological characteristics and physical properties of brick-concrete recycled coarse aggregate (BCRCA) composed of CBRCA and CCRCA. Morphological characteristics indexes of coarse aggregates including angularity, sphericity, texture and fractal dimension were described by digital image processing technique. The differences of morphological characteristic indexes among recycled coarse aggregates and natural crushed gravel coarse aggregate (NCGCA) were discussed. Results show that CBRCA has the highest void content, crushing index and water absorption among the four types of aggregates. Compared with NCGCA, recycled coarse aggregates have a higher angularity, lower sphericity and higher texture. The fractal dimension of recycled coarse aggregates is higher than NCGCA, indicating the complexity of shape of recycled coarse aggregates. Among the recycled coarse aggregates, CBRCA has the highest angularity and lowest sphericity, and CCRCA has the highest texture. The angularity and texture are significantly influenced by aggregate types. The sphericity and flatness ratio, as well as the angularity and texture have good positive correlation. The fractal dimension and elongation ratio, as well as the fractal dimension and sphericity have negative correlation. By testing two-dimensional indexes including fractal dimension and elongation ratio can easily reflect the morphological characteristics of coarse aggregates. When recycled coarse aggregates is used in building materials, the morphological characteristics should be carefully considered.