3D Printable Low-Carbon Concrete with Nano-silica Pretreated Recycled Fine Aggregates

With the advantages of reducing cost, time-saving, and lower labour requirements, 3D concrete printing is an emerging technology in global construction applications. It can be regarded as a sustainable construction approach of concrete. However, conventional printable cementitious materials contain considerable amounts of Portland cement for "guarantee" performance reasons, increasing the materials' cost and environmental impact. On the other side, it is a great challenge to handle the significant amount of construction and demolition (C&D) materials generated per year from local construction activities including in Hong Kong. The utilization of waste concrete as recycled aggregate (RA) is an effective approach to save natural resources, protect the environment and realise the sustainable development of the construction industry. Therefore, this current study pursued 3D printable low-carbon concrete printing approach by substituting 30% silica sand with RA. The RA was treated by soaking in 5% nano-silica slurry for 18 h and air-drying at a temperature of 28 +/- 2 degrees C and relative humidity of 85 +/- 5% for at least 7 days. It is revealed that the concrete with nano-silica treated RA has acceptable rheological properties and printability. Results can be concluded that 3D printable low-carbon concrete with good extrudability and acceptable buildability can be prepared by using nano-silica pretreated RA.