Use of treated recycled aggregates in high-strength concrete: a response surface approach

This research examines the application of treated recycled aggregates (TRAs) in concrete to decrease the consumption of natural aggregates, thereby promoting sustainability and improving material life cycle management. A novel two-stage mixing process is utilised, beginning with the pre-soaking of recycled aggregates in 3% acetic acid for 72 h to weaken the adhered mortar. This is succeeded by mechanical grinding using wire mesh brushes and iron balls in a drum mixer to enhance the quality of the aggregate. Experimental findings indicate that an increase in TRA replacement leads to a decline in workability, density, and durability. The slump reduces from over 75 mm at 0%–20% replacement to 50 mm at 50%–60%, and the density decreases from 2400 kg/m³ to below 2250 kg/m³. Water absorption increases from below 6% to 8%, resulting in a rise in sorptivity from 2% to 3.5%. Experimental analysis indicates that a 20% replacement of TRA and a revolution time of 20 min are optimal, resulting in a compressive strength of 50–55 MPa. Response surface analysis indicates significant effects of TRA replacement and revolution time (p-values < 0.05), demonstrating strong model reliability (R² > 0.90, low root mean square error).