Selected Issues of Recycled Unbound Aggregates in Earthworks Applications

Global consumption of aggregates is expected to exceed 60 billion metric tons by the end of 2024. The construction industry contributes to over half of this volume annually. The majority of it consists of natural quarried material; however, due to depleting resources of natural aggregates, cost, and high carbon footprint of the quarrying operation, recycled aggregate is becoming a popular alternative. In many applications, the specifications for the use of recycled aggregate are tight and there are no issues with the quality of recycled material when it arrives onto the construction site. However, in some applications problems with maintaining the quality of recycled aggregates appear. The consequence of poor-quality recycled aggregates being used with reduced geotechnical properties, compared to the design, is such that failures and accidents on sites can occur, that in a worst-case scenario can lead to serious H&S matters on the sites. The authors of this paper were involved in laboratory testing of poor-quality recycled aggregate that satisfies national standards for the specific class of aggregate. This exercise was undertaken to understand the variability of geotechnical properties of recycled aggregates and general performance. It was discovered that relying solely on particle size distribution, which is commonly used as acceptance criteria on construction sites for recycled aggregates, is not a good indicator of its geotechnical properties. Large-scale triaxial compression apparatus was utilized to investigate geotechnical properties of five different aggregates, which were sourced from various locations and countries. This paper describes the results of the study.