A Comparative Study of the Properties of Recycled Concrete Prepared with Nano-SiO₂ and CO₂ Cured Recycled Coarse Aggregates Subjected to Aggressive Ions Environment

This research focused on the modification effects on recycled concrete (RC) prepared with nano-SiO₂ and CO₂ cured recycled coarse aggregates (RCA) subjected to an aggressive ions environment. For this purpose, RCA was first simply crushed and modified by nano-SiO₂ and CO_2, respectively, and the compressive strength, ions permeability as well as the macro properties and features of the interface transition zone (ITZ) of RC were investigated after soaking in 3.5% NaCl solution and 5% Na₂SO₄ solution for 30 days, respectively. The results show that nano-SiO₂ modified RC displays higher compressive strength and ions penetration resistance than that treated by carbonation. Besides, we find that ions attack has a significant influence on the microcracks width and micro-hardness of the ITZ between old aggregate and old mortar. The surface topography, elemental distribution and micro-hardness demonstrate that nano-SiO₂ curing can significantly decrease the microcracks width as well as Cl^- and SO₄^2- penetration in ITZ, thus increasing the micro-hardness, compared with CO₂ treatment.