Abstract
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.
Highlights
The construction industry must find ways to re-use the concrete present in the huge amounts of demolition waste generated yearly
The accumulation of cement on the aggregate surface, and essentially on the surface of the adhered mortar, leads to a high concentration of alkalis in the interfacial transition zone (ITZ). The contact between these alkalis and the reactive siliceous aggregate may favour the early appearance of the alkali-silica reaction, which is the object of this study
The halos appeared around the mortar adhered to the recycled aggregate (Figure 2) when the recycled concrete was exposed to a high temperature (40 oC) at the same 100% relative humidity at which it was cured
Summary
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.
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