Role of Impact and Compression-Based Crushing on the Physical, Chemical, and Morphological Characteristics of Recycled Concrete Aggregates

Abstract

The main objective of this article is to study the role of the widely adopted crushing techniques, viz., impact and compression, on the physical, chemical, and morphological properties of recycled concrete aggregates (RCA). Five fundamental parameters of RCA, viz., hydrated cement-mortar paste (HCMP) concentration, specific density and absorption, aggregate comminution, chemical composition, and surface characteristics, were studied to achieve this objective. These parameters were studied for various coarse and fine RCA size ranges, including concrete fines. The results indicated that the shattering of concrete chunks in an impact crusher could lead to the production of well-graded RCA with less HCMP; this detached HCMP from coarser fractions was found to increase the reactivity of concrete fines by around 29%. In addition, the produced RCA was found to possess a high concentration of cubical and spherical particles. Both these benefits, i.e., lower HCMP and regular shape characteristics, were found to significantly affect the strength properties of recycled aggregate concrete. However, due to cleavage failure in compression crushing, coarser RCA with higher concentrations of blade and disc-shaped particles and higher HCMP content were produced. The fracture failure associated with compression crushing led to the production of less amorphous concrete fines with ∼45% higher quartz content. However, the fineness of these concrete fines was 44% higher, indicating its potential as a filler material. Interestingly, the HCMP was found to reduce the surface roughness of natural aggregates, and this might be one of the additional reasons for the poor interfacial transition zone between RCA and the new mortar matrix.