Multicriteria optimization of natural and recycled aggregate concrete for structural use Nikola To si c * , Sne zana Marinkovi c, Tina Da si c, Milo s Stani c University of Belgrade, Faculty of Civil Engineering, Bulevar kralja Aleksandra 73,11000 Belgrade, Serbia article info Article history: Received 22 January 2014 Received in revised form 13 October 2014 Accepted 27 October 2014 Available online xxx Keywords: Recycled aggregate concrete Transport scenario Life Cycle Assessment Multicriteria optimization VIKOR method Compromise solution abstract 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 mul- ticriteria 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. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Concrete is the most widely used construction material in the world. The data for the annual world production of concrete vary depending on the source between 6 billion (6 10 9 )(ISO, 2005) and 21 billion t (WBCSD, 2009). Among all human activities, the building industry has one of the largest environmental impacts: 40% of the raw stone, gravel and sand consumption; 25% of virgin wood; 40% of total energy and 16% of annual water con- sumption in the world (Dixit et al., 2010). Global annual con- sumption of aggregates is around 15 billion t (AGI, 2004). The question is raised then about the availability of natural aggre- gates (NA) and the effect of their production on the environment. On the other hand, construction and demolition (C&D) waste poses an increasing threat to the environment. In the EU alone, 850 million t of C&D waste is generated annually, which accounts for about 31% of the total waste generated (Fisher and Werge, 2011). The most common method of dealing with this waste is still land- filling. Recycling of C&D waste represents one way to convert waste into a resource. Waste concrete cannot be recycled back into its original constituent materials or original whole form. Rather, con- crete is crushed into aggregate called recycled concrete aggregate (RCA) for use in new applications. The production of RCA usually includes a two-stage crushing and sieving process and a removal of any impurities such as steel, wood, gypsum, masonry, glass etc. During the crushing of concrete waste a certain quantity of cement paste remains attached to the aggregate. This residual cement paste is the main cause of the lower quality of RCA compared to NA. Compared to natural aggregate, recycled concrete aggregates have on average a 10% lower density (Poon and Lam, 2008). Water absorption ranges from 3.5% (Rahal, 2007) to 10% (Xiao et al., 2005) in the case of coarse RCA and from 5.5% (Yang et al., 2008) to 13% (Evangelista and Brito, 2007) in the case of fine RCA. * Corresponding author. Postal address: Faculty of Civil Engineering, Bulevar kralja Aleksandra 73, 11000 Belgrade, Serbia. Tel.: þ381 11 3218 501; fax: þ381 11 3370 253. E-mail addresses: ntosic@imk.grf.bg.ac.rs (N. Tosic), sneska@imk.grf.bg.ac.rs (S. Marinkovic), mtina@grf.bg.ac.rs (T. Dasic), mstanic@grf.bg.ac.rs (M. Stanic). Contents lists available at ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro http://dx.doi.org/10.1016/j.jclepro.2014.10.070 0959-6526/© 2014 Elsevier Ltd. All rights reserved. Journal of Cleaner Production xxx (2014) 1e11 Please cite this article in press as: Tosic, N., et al., Multicriteria optimization of natural and recycled aggregate concrete for structural use, Journal of Cleaner Production (2014), http://dx.doi.org/10.1016/j.jclepro.2014.10.070