The modification effects of a nano-silica slurry on microstructure, strength, and strain development of recycled aggregate concrete applied in an enlarged structural test

• Recycled aggregate concrete (RAC) modified by nano-silica was applied in a project.
• Mechanical properties of RAC were improved after modification.
• The cracking resistance of the modified RAC beam was enhanced.
• Nano-silica enhanced the new interface between the old and new mortars in RAC.

The modification effects of a nano-silica slurry on properties of recycled aggregate concrete (RAC) were experimentally studied. Together with natural aggregate concrete (NAC), non-modified and modified RAC were applied in three beams in a real project. The beneficial effects of the nano-silica slurry on RAC’s mechanical properties were certificated. In situ strain monitoring in the target beams showed the improved resistance to cracking of RAC after modification. Nanoindentation tests proved that the nano-silica slurry enhanced the new interface transition zone (ITZ) between the old and new mortars in RAC, and surface-strengthened the old mortar, while the old ITZ between old aggregate was not strengthened.