Green and Digital Transformation Towards Circular Economy in the Construction Industry: Upcycling of Construction and Demolition Wastes From Diverse Sources and Their Integration Into 3D Printing Technology

Abstract

At the nexus of society, the environment, and urban development, the construction sector constitutes a colossal economy and faces substantial challenges due to the need to accommodate a growing population and displaced individuals from natural disasters, political instability, and other causes. This primary industry is responsible for the largest waste stream, Construction and Demolition Waste (CDW), which accounts for over a third of all waste in the EU. Therefore, urgent action is required to implement feasible and sustainable management strategies to address the challenges associated with its inappropriate management. At this point, 3D concrete printing poses promising potential to address common challenges such as affordable housing, rapid construction and the construction industry's transition to a circular economy by integrating waste-based printable materials.

With a focus on Green and Digital Transformation in the construction sector, this thesis aims to pave the way toward a circular, sustainable, and digital construction industry by generating solutions through the upcycling of CDW and their integration to the 3D concrete printing technology. In this context, the initial focus was on characterizing CDWs from various sources with significantly varying characteristics for use in development of environment-friendly building materials via geopolymerization technique. The effect of varying chemical contents of CDW from different sources on the mechanical performance of the final product was investigated and optimal conditions were determined based on these variations. Sustainable mortar phases were then developed by incorporating fine recycled concrete aggregates derived from CDW based waste concrete, and the mechanical performance was evaluated considering the influences of the recycled aggregates size and content. In addition, a Life Cycle Assessment (LCA) was conducted to determine the extent of sustainability of each component and its environmental impacts. The final phase entailed the assessment of viability of CDW-based geopolymer concept, extensively investigated in preceding stages, for application to CDW sourced from a distinct geographical region, namely the Netherlands. Moreover, it involves the development of a one-part (just-add-water) CDW-based geopolymer mortar to be integrated into the developed systems for use in a 3D concrete printing technique, facilitating the green and digital transformation of the construction industry in line with the principles of the circular economy.

According to the findings, the mechanical performance of geopolymerized CDW is strongly influenced CDW's intrinsic parameters, which vary depending on source; optimization of related parameters ensures consistent, high performances. LCA analysis demonstrate that, alkaline activators had the highest contribution on environmental impact, followed by CDW treatment; however, impacts could be reduced with mixture design optimization. Furthermore, 62.9% reduction in CO2 emissions was achieved compared to Portland cement-based systems with similar strength class and embodied energy. The mechanical performance of the one-part geopolymer mixture varied due to the anisotropy; however, these variations could be minimized by optimizing the layer height. Reducing the layer height can minimize the formation of distributed defective regions in the interlayer bonding area caused by the coalescence and expansion of pores, enabling the 3D printed specimens to exhibit fracture behavior as if there were no weak interlayer bond region.