Technical indexes and requirements for the application of recycled construction and demolition waste in base layers of roads in China

The large-scale generation of construction and demolition waste (C&DW) in China has promoted increasing interest in its application in road base layers. Recycled construction and demolition waste (RC&DW) has been incorporated into national and provincial technical specifications; however, the corresponding technical indices and threshold requirements vary significantly among regions, which limits their effective application in engineering. This study provides a systematic review of technical indices and requirement ranges for RC&DW used in road base layers in China based on 35 national and provincial specifications. Crushing value, water absorption, elongated or flaky particles, content of lightweight impurities, and fine powder content are primarily used and recommended for evaluating the performance of recycled coarse aggregate (RCA). In contrast, the critical indices for recycled fine aggregate (RFA) are the sand equivalent and the 0.075 mm plasticity index. In the cement-stabilized RC&DW, the 7 d unconfined compressive strength is affected by the coupling between road grade and traffic volume. In other cases, it is constrained by either the road grade or traffic volume alone. Road grade, traffic volume, and coupling classifications are used to establish the compaction degree requirements for cement-stabilized RC&DW, considering both road grade and traffic volume. Based on the statistical synthesis of existing specifications, recommended index ranges and classification schemes are proposed for practical reference. The results indicate that significant dispersion exists in RC&DW technical requirements, primarily due to differences in material sources, regional management levels, and road class demands. This review highlights the necessity of harmonizing technical requirements while allowing appropriate flexibility to accommodate material heterogeneity. The findings provide a reference for improving specification consistency and promoting the standardized application of RC&DW in base layers of roads under Chinese engineering conditions.