Effects of coral, recycled and natural coarse aggregates on the mechanical properties of concrete

Abstract

The effects of different types of coarse aggregates on mechanical properties of concrete were compared in this paper. Three different coarse aggregates were considered: natural coarse aggregate (NCA), recycled coarse aggregate (RCA) and coral coarse aggregate (CCA). An experimental campaign was developed involving uniaxial compression tests and the use of digital image correlation (DIC) method to obtain the deformation distribution and crack propagation of specimen. The influence of coarse aggregate on deformation development of concrete phases (cement mortar and interface transition zone (ITZ), etc.) was also studied. Test results indicated stress-strain curve (SSC) of concrete using NCA (natural aggregate concrete) was similar to that of concrete adopting RCA (recycled aggregate concrete), while SSC of coral aggregate concrete (concrete using CCA) was different from the others. Compared with coral aggregate concrete (CAC), the failures of natural aggregate concrete (NAC) and recycled aggregate concrete (RAC) were more ductile. But prismatic compressive strength of CAC was higher than other specimens. Coarse aggregate type had obvious influence on the distribution of axial deformation fields of concrete. It indicated that the axial displacements of cement mortar and ITZ were higher than that of NCA before peak point. After mixing different types of coarse aggregates, obvious changes were not found in the displacement distribution of specimen. It was also found that the large strains (axial and transverse) of NAC and RAC mainly concentrated in cement mortar and ITZs before peak stress, however, those of CAC obviously appeared in CCA. Type of coarse aggregate changed the crack propagation of concrete. Compared with NAC and RAC, CAC cracking seldom appeared before peak stress, and cracks drastically expanded to critical size after that. Finally, a normalized analytical expression for different types of concretes was suggested, which could provide a basis for the application of recycled and coral aggregate concretes.