Comparative environmental evaluation of aggregate production from recycled waste materials and virgin sources by LCA

The management of construction and demolition (C&D) waste and waste glass is a serious concern in Hong Kong, as well as other countries due to their non-combustible and non-putrescible nature, and the running out of disposal outlets. However, mineral wastes derived from C&D activities and waste glass are considered to have potential to be re-used as construction materials, especially as aggregates. In addition, Hong Kong urgently needs alternative and sustainable sources of aggregate, as the local quarry sites for aggregate production are expected to be exhausted soon. Many experimental studies have demonstrated that recycled aggregates from C&D waste and waste glass can be potentially recycled for various engineering applications in Hong Kong, but no study has yet attempted to assess the sustainability by lifecycle assessment (LCA) techniques. In order to increase the environmental awareness in the construction industry, assessment of the environmental performance of construction materials by LCA is therefore needed. The present study was conducted to assess and compare the environmental consequences of recycled aggregates production from C&D waste and waste glass, and natural aggregate production from virgin materials by LCA by using case specific and first hand data. The results reveal that compared with natural coarse aggregates, recycled coarse aggregates produced from C&D waste reduce 65% greenhouse gases (GHGs) emission with a saving of 58% non-renewable energy consumption. Similar environmental benefits are observed for producing recycled fine aggregates from C&D waste. In addition, compared with the production of natural fine aggregates from river sand, producing recycled fine aggregates from waste glass saves 54% energy consumption and reduces 61% GHGs, and 46% SO2eq emissions. According to the IMPACT 2002+ Method, significant health, resource, climate change and ecosystem damages can be saved in producing recycled aggregates from both waste materials compared to producing and importing aggregates from virgin sources. This is the first ever LCA study on producing recycled aggregates from waste glass. Therefore, it can be concluded that substantial net environmental benefits can be realized for producing recycled aggregates from C&D waste and waste glass. The results can provide a guidance to maximize C&D waste and waste glass recycling, resourceful treatment of wastes and conserve natural resources.