Evaluation of Mechanical and Durability Properties of Concrete Incorporating CO</sub>-treated Recycled Concrete Aggregates

The increasing demand for sustainable construction materials has heightened interest in using recycled concrete aggregates (RCA) as viable replacements for natural aggregates. However, RCA’s inherently higher porosity, elevated residual mortar content (RMC), and reduced mechanical properties have traditionally limited its use in structural and pavement concrete. This research systematically investigates improving RCA properties through CO2 carbonation treatment to enhance both mechanical and durability performance. Unlike prior studies that focused on limited sources or small-scale setups, this study evaluates RCA from four distinct infrastructure sources, including highway and airfield pavements, applying accelerated carbonation treatments at mid-scale and commercial-scale chambers under control conditions. The investigation involved detailed characterization of RCA before and after treatment, assessing specific gravity, water absorption, residual mortar content (RMC), aggregate crushing value (ACV), and freeze-thaw (FT) mass loss. Lab-scale carbonation was applied to seven RCA sources, while mid- and commercial-scale treatments were conducted on four selected sources. Concrete mixtures incorporating 25%, 50%, or 75% untreated and CO2-treated RCA were prepared and tested alongside a control mix meeting the Nebraska Department of Transportation (NDOT) 47B standard. Performance evaluations included fresh properties, compressive and flexural strengths, drying shrinkage, rapid chloride ion penetration, surface resistivity, and freeze-thaw durability. Results show that CO2 carbonation improved RCA quality by reducing water absorption, enhancing freeze-thaw resistance, and increasing ACV. The Concrete with treated RCA demonstrated superior durability, notably in freeze-thaw resistance, chloride ion penetration, and surface resistivity, achieving or surpassing NDOT performance benchmarks. Treated RCA not only improved durability but also enabled the use of higher RCA replacement percentages in concrete, meeting all performance requirements. Field validation on pavement sections at Lincoln West A Street and the 60th Street Approach Road confirmed laboratory findings, with CO2-treated RCA concrete delivering mechanical strength and durability comparable to conventional natural aggregate pavements. By demonstrating the scalability of carbonation treatments from lab to industrial levels and validating performance in field applications, this research positions CO2-treated RCA as a sustainable, durable, and scalable material for resilient pavement construction, supporting its broader adoption in sustainable infrastructure development. Advisor: Jiong Hu