Evaluating the feasibility, usability, and strength of recycled construction and demolition waste in base and subbase courses

Abstract

Demolition and repairing of buildings produce large amounts of construction and demolition waste. The produced debris not only takes up space, but also leads to environmental degradation, unpleasant scenery, and above all, waste of construction materials and money. In this regard, recycling is a good solution that has received less attention in the construction section than other sections of industry. In road construction, part of the large amount of aggregates used in pavements can be provided from recycled construction and demolition (C&D) Waste. The aim of this laboratory study was to evaluate feasibility and usability of C&D in base and subbase courses of pavement. For this purpose, usable C&D materials were separated and the proportion of each was determined. Each material was passed through a crusher and a 25 mm sieve. The segregated materials were then mixed and technical specifications of the mixture were controlled against AASHTO standards. Finally, mix proportions were determined so that AASHTO technical specifications were satisfied. For this purpose, different percentages of C&D were mixed with control sample materials and technical specifications of the result were evaluated using compaction, California bearing ratio (CBR), and resilient modulus tests. The results showed the necessity of C&D decomposition, using crusher and sieve to control maximum grain size allowed, and exclusion of materials not complying with technical standards, before performing strength evaluations. Proportions of waste components must be selected so that all technical specifications are satisfied. Sometimes it might be necessary to mix waste materials with additional standard ones to achieve a technically standard final result. In this study, compaction and CBR tests showed that the obtained mixture is suitable for use in base and subbase layers but minimum requirements of resilient modulus for the base course are not met. Alterations in mixture components resulted in a significant reduction in C&D content for the base course. Therefore, it is recommended that C&D is used only in subbase layers of pavements.