Influence of incorporation of nano-silica and recycled aggregates on compressive strength and microstructure of concrete

• Scanning electron microscopy and Vickers microhardness test is used in this study.
• Microhardness values of ITZ of RAC mixes are lesser than NAC mixes.
• The porosity and unhydrated cement quantity of ITZ is more for RAC mixes.
• Nano-silica reduces porosity and unhydrated cement quantity across ITZ.
• Microstructure of ITZ improves with the incorporation of nano-silica.

The present investigation deals with the study of compressive strength and characteristics of the Interfacial Transition Zone (ITZ) of concrete containing recycled aggregates and nano-silica. For this purpose, compressive strength at 7, 28, 90 and 365 days are determined for fully natural and recycled aggregate concrete mixes made with or without nano-silica. In addition to above, Vickers microhardness test and backscattered-mode scanning electron microscopic analysis is carried to characterize ITZ of concrete mixes. The results of study depict that full replacement of natural coarse aggregates with recycled ones have significant effect on compressive strength and ITZ characteristics of concrete. However, compressive strength and microstructure of concrete mixes improves with the incorporation of nano-silica.