Effect of microstructure of ITZ on compressive strength of concrete prepared with recycled aggregates

摘要

Concrete specimens were prepared with a recycled normal-strength concrete (NC) aggregate, a recycled high performance concrete (HPC) aggregate and a natural aggregate (NA) as control. The influence of these aggregates (recycled and natural) on the microstructure and compressive strength of the new concrete were studied. SEM observations revealed that the NC aggregate-cement interfacial zone consisted mainly of loose and porous hydrates whereas the HPC aggregate-cement interfacial zone consisted mainly of dense hydrates. The compressive strength results that the concrete prepared with natural aggregates was higher than that of the recycled aggregate concrete. Also, the strength development of the HPC recycled aggregate concrete was faster than that of the NC recycled aggregate concrete. At 90 days, the HPC recycled aggregates concrete achieved similar strength values to the natural aggregate concrete. The results are explained by the differences in porosity and pore structure of the two types of aggregates, and possible interactions between the aggregates and the cement paste.