Strength, Chloride Ion Penetration, and Nanoscale Characteristics of Concrete Prepared with Nano-Silica Slurry Pre-Coated Recycled Aggregate

It has become a feasible green building development strategy to prepare recycled aggregate concrete (RAC) by processing construction and demolition (C&D) wastes into a recycled coarse aggregate (RCA). On the other hand, defects such as low strength and easy cracking of RAC seriously limit its application in construction materials. In this paper, RCA was strengthened by pre-coated nano-silica (NS) slurry to improve RAC performance. The effect of nano-modified recycled coarse aggregate (MRCA) on concrete compressive strength and chloride ion penetration after replacing ordinary RCA or natural coarse aggregate (NCA) was studied. The SEM, MIP and nano-indentation techniques were used to evaluate the effect of MRCA in concrete. The results show that the replacement of NCA with RCA or MRCA reduces the mechanical property and chloride ion penetration of concrete. Under the same conditions, the mechanical property and chloride ion penetration of nano-modified recycled aggregate concrete (MRAC) are better than those of RAC. Compared with RAC, the width of interface transition zone (ITZ) and indentation modulus of MRAC increased by 23.1% and 89.4%. This is mainly attributed to the filling effect of NS slurry, which reduces the number of pores and microfractures on the surface of RCA, and the pozzolanic effect of NS consumes part of calcium hydroxide to produce more calcium silicate hydrate gel, which improves the ITZ of RAC. In addition, the use of NS slurry pre-coating modified RCA has good economic and environmental benefits.