Evaluating Circularity of Plastic Use in Traditional and Modular Urban Construction Through Micro-Indicators

The transition to a circular economy (CE) is a critical challenge for the urban built environment, particularly within the Building and Construction sector. This study explores the application of circularity micro-indicators to assess the use of plastic materials in two Portuguese construction approaches: traditional (CS1) and modular (CS2). A set of four relevant micro-indicators—Material Circularity Indicator (MCI), Recycled Content Performance Indicator (RPI), Circular Design Guidelines (CDG), and Circular Economy Implementation Potential (CEIP)—was selected to evaluate material circularity at the product and system levels. The novelty of this study lies in selecting and applying the most relevant circularity indicators from the literature to plastic products in construction, providing the first practical demonstration of their use and offering actionable tools to support stakeholders in material selection, design decisions, and circularity assessment. Findings show that modular construction demonstrates a stronger alignment with CE principles compared to traditional methods, although both cases present low overall levels of circularity. For instance, the Material Circularity Indicator (MCI) ranged from 8.4% in the traditional building (CS1) to 15.2% in the modular building (CS2), quantitatively illustrating the circularity potential of modular construction. Key strategic opportunities for improvement include design for disassembly, the elimination of toxic or scarce materials, improved recyclability of plastic components, and the integration of on-site material separation and recovery zones. Strengthening waste management systems is also essential to enhance the quality and reliability of recycled plastic materials. The study highlights the value of micro-indicators as practical tools to support evidence-based decision-making in material selection, design strategies, and circular construction planning. By guiding more sustainable practices in urban construction, these indicators can play a pivotal role in accelerating the sector’s transition toward a circular and resource-efficient economy. Methodologically, the study adopts a collaborative case-study approach with an industry partner, involving brainstorming sessions with experts in CE and circularity indicators to select representative buildings, and identify indicators from the literature based on data availability and relevance for construction plastic products, which are then applied to real project data, complemented by exploratory improvement scenarios.