Sustainable decision-making through stochastic simulation: Transporting vs. recycling aggregates for Portland cement concrete in underground mining projects

Abstract

The procurement of high-quality aggregates is a global problem. In Chile, mining companies are in theprocess of developing massive underground projects that require the extensive use of Portland cementconcrete (PCC), approximately 60%e75% of which is aggregate. Currently, mining projects transport allthe required aggregate to the site from stockpiles that can be more than 100 km away, while miningexcavations produce millions of cubic meters of waste rock (WR) that are disposed of in landfills. The useof WR in PCC seems to be a sustainable solution for the production of PCC, but decision-makers lack thetools to support a sustainable decision based on CO2 emissions and operation costs.This paper proposes a methodology that uses stochastic simulation tools to evaluate CO2 emissionsand operation costs to decide when it is sustainable to use WR in PCC for underground mining projects.The main objective of this paper is to provide a methodology to quantify CO2 emissions and the cost oftransporting natural aggregate versus recycling WR for PCC production in tunneling operations. Asensitivity analysis is also presented, which considers scenarios that include natural aggregate transportationdistances of 50, 60, 70, 80, 90, and 100 km, and 0%, 25%, 50%, 75%, and 100% replacement ofnatural aggregate with recycled WR in PCC. The results indicate that the use of WR leads to reductions inCO2 emissions only for natural aggregate transportation distances of greater than 70 km owing to theemissions produced when recycling WR. In addition, 100% replacement of natural aggregate withrecycled WR leads to a greater reduction in CO2 emissions than that obtained in scenarios in which apercentage of the required natural aggregate is obtained from WR. In terms of costs, 100% replacement ofnatural aggregate with recycled WR is the most economical alternative for most scenarios; however, thecost reduction varies with the required transportation distance of natural aggregate. It is concluded thatusing 100% recycled WR in PCC leads to lower CO2 emissions and costs as compared to the traditionalapproach in which the natural aggregate is procured from a site located at a distance of 70 km or morefrom the construction site, under model assumptions.