Durability studies on recycled fine aggregate concrete

Abstract

The use of recycled fine aggregates (RFA) from construction and demolition(C&D) waste in concrete gaining importance from past decades. The presence of excessive fines and old adhered mortar in RFA, make mediocre properties of RFA concrete. The influencing properties of RFA concrete on different durability aspects lacks research data. Several studies have quoted the unfavourable performance of RFA in concrete particularly in respect to shrinkage, permeability, chloride penetration. Whereas, most of the durability studies of recycled coarse aggregates (RCA) concrete are well established. Therefore, the aim of this paper is to study the judicious use of RFA in concrete and its performance in different durability environments. RFA is one of the major alternative materials that is produced in huge amount and can be utilized effectively with some additional care. Alkali silica reaction, porosity, water permeability, acid-alkaline immersion, drying shrinkage, rapid chlorine penetration, surface electrical resistivity and carbonation along with their microstructural changes were evaluated to understand the influence of RFA in concrete. The outcomes exhibited that increment in RFA content in concrete negatively distress its durability. Nevertheless, as the age of the concrete increases the resistance to water, chlorine and carbonation resistance increases. The optimum replacement of river sand by RFA in concrete was 30% (RFA30). The reduction in shrinkage and porosity were in order of 14%, and 25% respectively. The RFA30 was 21.25% higher resistance to chlorine penetration than control concrete. Micrograph illustrated highly distorted CSH and weak ITZ and voids, when 100% replacement of river sand with RFA after immersing them in concentrated HCl, H2SO4 at 90 days. However, dense microstructure with less voids were observed after immersing in NaOH.