Properties of recycled concrete aggregates strengthened by different types of pozzolan slurry

Abstract

Abstract Recycled concrete aggregate (RCA) retrieved from construction and demolition concrete wastes is widely used as an alternative to natural aggregate (NA) in the construction industry. However, the weak adhered mortar adversely affects the properties of RCA, which has a detrimental effect on the performance of resultant concrete. This paper aims to strengthen the weak adhered mortar and improve the properties of RCA by using an economic and environmentally friendly technique. Soaking RCA in different types of pozzolan slurries (i.e., fly ash, silica fume, and nano-silica fume) at different dosages and soaking times is the proposed technique to enhance the RCA quality. The physical and mechanical properties of RCA were comprehensively assessed before and after the surface treatment. Meanwhile, the surface morphology of RCA was characterized by using scanning electron microscope with energy dispersive spectroscopy (SEM-EDS) to examine the effect of this technique on the micro properties of RCA surface. Results indicate that the pozzolan slurry soaking methods can generally help to strengthen the weak adhered mortar and thus enhance the RCA properties. On trialing various pozzolan slurries and treatment duration, it is found that the 40% FA&C and 3% NSF slurries with 4 h soaking time can render an obvious effect, e.g. with more than 50–55% lowering of water absorption, 10–11% increasing particle densities, respectively. 40% FA&SF, 40% FA&C and 3% NSF slurries with 4 h soaking time exhibited a comparable improving performance, e.g. with 31, 35, 33% lowering of abrasion values, respectively. Obvious microstructure enhancement was also observed in the treated RCA where surface homogeneity and reduced Ca/Si ratio are found. The physical properties of RCA including water absorption and porosity are strongly correlated with the mechanical and durability characteristics in terms of resistance to crushing and abrasion values through conducting the proposed treatment technique.