Life cycle sustainable assessment of natural vs artificial lightweight aggregates

Abstract

Optimal selection of concrete aggregates can promote sustainable construction practice from the bottom line, which is a feasible strategy to cope with resources crisis and solid waste pollution. In this study, a two-level tree structure framework was thus proposed for the sustainability assessment of lightweight aggregates (LWA) based on the life cycle assessment concept. The evaluation system was divided into four criteria categories marked as society demands, economic costs, environmental impacts and technical performance, and each of them was assigned a number of sub-index. A qualitative questionnaire survey with seven sub-index and a quantitative calculation with eight sub-index were executed in the target system. Sintering fly ash aggregates (SFFAA), cold-bonding fly ash aggregates (CBFAA), waste clay brick aggregates (WCBA) and natural pumice aggregates (NPA) were chosen as typical artificial and natural lightweight aggregates objectives and evaluated in the framework. Impact and sensitivity analyses were conducted to comparably discuss the sustainability of various lightweight aggregates. The impact analyses represented that the waste clay brick aggregate has better sustainability. The sensitivity analysis shows that the supply-demand relationship of raw materials greatly impacts the sustainability of lightweight aggregate, and the transportation distance of raw materials is the critical factor in the production of LWA. At the same time, artificial lightweight aggregates are sensitive to cement binder consumption, and zero cement addition or waste cement powder is an optimistic option. From the sustainable life cycle assessment results, waste clay brick aggregates, sintering fly ash aggregates and cold-bonding fly ash aggregates are suggested as the alternative to the natural pumice aggregates for the lightweight aggregates concrete production. The emphasis on the weight of the social dimension will tend to prefer the selection of SFAA, and the economic or environmental dimension will lead to the preference of CBFAA for sustainable development. The framework proposed in this work could be used in choosing other sustainable construction materials or cleaner products.