Alkali silica reaction in concrete induced by mortar adhered to recycled aggregate

The durability of recycled concrete must be determined before this material can be used in construction. In this paper the alkali-silica reaction in recycled concrete is analyzed. The recycled concrete is made with recycled aggregates, composed by original limestone aggregates and adhered mortar with reactive silica sand, and high alkali content cement. Due to the manufacturing process used for concrete production and the high water absorption capacity of recycled aggregates, cement accumulation happens in the interface (ITZ). The concentration of alkalis on the surface of recycled aggregates-ITZ and the presence of reactive sand in the mortar adhering to the recycled aggregate induce an alkali-silica reaction in 6-month concrete. The existence of this reaction is confirmed by environmental scanning electron microscopy (ESEM) and EDX analysis. The mechanical properties of 6-month recycled concrete were similar to those values at 28-days of curing.