Workability and Strength of Ultra-High-Performance Concrete Containing Nano-Ca(OH)2-Modified Recycled Fine Aggregate

To improve the surface properties of recycled fine aggregates (RFAs), it is better to replace natural aggregates for the preparation of ultra-high-performance concrete (UHPC). The feasible modification method of RFA carbonization after being soaked in nano calcium hydroxide (nano-CH) solution (ICRFA) is investigated. Untreated RFA (URFA) and carbon dioxide-treated RFA were the control groups. The results revealed that the pores of RFA were filled by calcium carbonate (CaCO3) generated from the carbonization of nano-CH. The total porosity and the contents of harmful pores and multi-harmful pores of UHPC were reduced. Furthermore, the effective water-binder ratio (w/b) of UHPC with RFA was higher than that of UHPC with ICRFA. Therefore, the compressive strength of UHPC with ICRFA at 28 days was significantly higher than that of UHPC with URFA. The modification method of ICRFA is a more effective and economical method for improving compressive strength than that of CO2-treated RFA (CRFA).