Improvement of mechanical and interfacial properties (ITZ) of concrete based on treated recycled aggregates

Abstract

The increasing utilization of solid waste from construction and demolition as a raw material for aggregate production for concrete is generating growing interest in the construction and public works industry. This practice contributes to preserving natural resources and reducing waste, which is essential for environmental protection. The use of recycled concrete aggregate (RCA) from demolition waste to produce new concrete, known as recycled aggregates concrete (RAC), is an eco-friendly approach. However, RCAs have poor physical and mechanical properties due to their low density and high absorption, compounded by a low interfacial transition zone (ITZ) compared to natural aggregates (NA). To address these issues, this study proposes encapsulating RCA in a cement slurry (with a water-to-cement ratio of 0.5) and examining the impact of adding 5% silica fume (SF) and 2% water-repellent agent (HF) to the cement grout on the properties of (RCA) made from treated recycled concrete aggregates (RCAT). Two types of treated aggregates, (RCAT-5%FS) and (RCAT-2%HF), were developed and hardened for 15 days in air. They were then used to manufacture RACT concrete. The experimental results demonstrate that the inclusion of (SF) and (HF) effectively enhances the properties of (RCAT). Moreover, the compressive and tensile strengths of RACT-SF are greater than those of the control concrete NAC, estimated at 43.5 MPa and 3.87 MPa, respectively. SEM-EDS analysis confirmed the uniformity of contacts within (ITZ) and assessed the compatibility of the Ca/Si ratio. The addition of silica fume contributed to the creation of solid, durable, and environmentally friendly concrete.