Department of Civil and Mineral Engineering, University of Toronto, Toronto M5S 1A4, Canada.
Environ Sci Technol. 2020 Oct 20;54(20):12840-12849. doi: 10.1021/acs.est.0c01670. Epub 2020 Sep 28.
Green policies currently incentivize concrete producers to replace portland cement with industrial byproducts to reduce their greenhouse gas (GHG) emissions. However, policies are based on attributional life cycle assessments (LCAs) that do not account for market constraints and consider byproducts either available burden-free to the user (cutoff approach) or partially responsible for the emissions generated in the upstream processes (allocation). The goal of this study was to investigate whether these approaches (and incentives) could lead to a mismanagement of byproducts and to suboptimal solutions in terms of regional GHG emissions. The use of ground granulated blast-furnace slag (GGBS) in Ontario was studied, and an optimization model to find the least GHG-intense way of using GGBS was developed. Results showed that producers should replace 30 to 40% of portland cement in high-strength concrete to minimize the regional GHG emissions associated with concrete. However, traditional LCA approaches do not suggest this solution and are estimated to lead to up to a 10% increase in concrete GHG emissions in Ontario. The substitution method, which assigns emissions or credits to byproducts based on emissions associated with the products they may displace, can yield decisions consistent with the regional emission optimization model. A revision of current policies is recommended to include market constraints.
绿色政策目前鼓励混凝土生产商用工业副产品替代波特兰水泥，以减少其温室气体（GHG）排放。然而，这些政策是基于归因生命周期评估（LCA）的，没有考虑到市场限制，并且认为副产品要么免费提供给用户（截止方法），要么对上游工艺产生的排放负有部分责任（分配）。本研究的目的是调查这些方法（和激励措施）是否会导致副产品管理不善，并导致区域温室气体排放的次优解决方案。研究了安大略省使用粒化高炉矿渣（GGBS）的情况，并开发了一个优化模型，以找到使用 GGBS 的温室气体排放强度最低的方法。结果表明，生产商应该在高强度混凝土中取代 30%至 40%的波特兰水泥，以最大限度地减少与混凝土相关的区域温室气体排放。然而，传统的 LCA 方法并没有提出这种解决方案，据估计，这将导致安大略省混凝土温室气体排放增加 10%。替代方法根据它们可能替代的产品的排放情况，将排放或信用分配给副产品，从而可以做出与区域排放优化模型一致的决策。建议修订现行政策，纳入市场限制。
