A physical, low-environmental-impact, and easily applicable technology for enhancing the performance of recycled concrete: Multiscale insights

• Under the same original mixture, compression casting concrete technology increased the compressive strength of RAC by more than 80%. • The mechanisms of how the compression casting concrete technology increased the strength of RAC were uncovered based on multi-scale investigations. • A molecular dynamics (MD) simulation model was developed for compression-cast RAC. • Life cycle assessment considering uncertainty was conducted to confirm the environmental benefits of compression-cast RAC. A simple and economical approach to improving the performance of recycled aggregate concrete (RAC) with a low environmental burden is crucial for the sustainable development of the construction industry. This study adopts the recently developed purely physical compression cast (CC) technology to improve both the mechanical and environmental performance of RAC without adding any supplementary cementitious materials. Uniaxial compression tests, microstructure characterizations, molecular dynamics (MD) simulation, and environmental impact assessments were conducted to demonstrate the effectiveness of CC technology, uncover its enhancement mechanisms, and quantify its environmental benefits. The mechanical test results reveal that the compressive strength and elastic modulus of RAC increased by 84.78%-88.11% and 2.14%-31.47%, respectively, under CC compared to the normal cast RAC with the same original concrete mix. These enhancements primarily result from the compactness of ingredients in fresh concrete, and to a lesser extent, from the reduced water-to-cement ( w / c ) ratio. Microscopic characterizations and MD simulations demonstrate that CC significantly reduces the porosity of the mortar matrix and interfacial transition zone (ITZ), while markedly enhancing the bonding capacity of the ITZ. Furthermore, the CO 2 emissions and energy consumption of RAC under compression casting were both reduced by approximately 46.8% per unit strength compared to the normal cast RAC. Besides, the corresponding benefit potential is significant with a probability of 100%, highlighting a remarkable sustainability advantage.