Influence of Aggregate Composition on the Properties of Recycled Concrete and Improving Performance Using Special Additives

The principles of the circular economy and the effective utilization of construction and demolition waste are becoming increasingly important, as evidenced by a growing body of research in this field. However, studies focusing on the waterproofing properties and setting times of recycled concrete derived from various construction and demolition waste sources remain scarce. This research investigates the characteristics of recycled aggregates from different origins and explores how these characteristics influence the properties of concrete. The study examines the effects of pre-soaking aggregates to saturation, the incorporation of water absorption-reducing additives, and the ratio of recycled aggregates to natural aggregates on the properties of both fresh and hardened concrete. Laboratory tests were conducted on crushed recycled concrete aggregates (RCA), confirming that concrete produced with recycled aggregates can meet standard requirements for compressive strength and water resistance exposure classes despite the recycled aggregates themselves not meeting the required standards. The results were used to calculate an effective water-cement ratio and establish a correlation between this ratio and compressive strength. The findings indicated that the compressive strength of mixtures approached, and in most instances exceeded, that of the reference concrete utilizing natural aggregates. Specifically, the reference concrete (REF-1) achieved a compressive strength value of 51.4 MPa after 28 days, whereas the 30% recycled mixture (REC-10), made from pure concrete demolition waste, produced a compressive strength of 62.7 MPa. The maximum water penetration depth of the REC-10 mixture was measured at 11 mm, in comparison to 15 mm for the reference mixture (REF-1). Additionally, the initial setting time of the mixtures incorporating special additives reached the 80 min threshold. The practical aspects of this research examined potential industrial applications that do not necessitate special aggregate treatments, thus maintaining the water-cement ratio within acceptable limits. This study evaluates the feasibility of utilizing recycled concrete aggregates (RCA) from construction waste to produce concrete that satisfies the standard requirements for compressive strength and water resistance. It assesses the impact of RCA on performance, provides industrial insights, and suggests potential regulatory revisions.