Multicriteria optimization of natural and recycled aggregate concrete for structural use

Recycling of concrete waste to produce recycled concrete aggregates (RCA) and its use in the production of structural concrete is the way towards reducing the depletion of natural mineral resources and the amount of construction and demolition waste being land-filled. The goal of this study was to determine the optimal choice of aggregate type and transport scenario in concrete production, employing a multicriteria optimization method taking into account technical, economical and environmental limits and constraints. Several concrete types with different type of used aggregate (river aggregate, crushed stone and recycled concrete aggregate) and different transport scenarios were analyzed. The environmental system evaluation criteria were chosen according to the Life Cycle Assessment methodology and the economical system evaluation criteria were determined in accordance with the current state of the ready-mixed concrete market in Serbia. The normative multicriteria optimization method (VIKOR method) was employed to determine the optimal solution. Analysis was performed for different decision making scenarios that gave emphasis to different criteria. Results have shown that concrete with a 50% replacement ratio of coarse aggregate with RCA can be presented as an optimal solution. Since natural aggregate concrete made with river aggregate was shown to have the lowest price, a further analysis was conducted to determine what economical measures should be undertaken in order to achieve cost equality of recycled and natural aggregate concrete. The analysis identified taxes on river aggregate, taxes on land-filling and subsidies for using RCA as viable measures.