Life-Cycle Assessment of the Substitution of Sand with Coal Bottom Ash in Concrete: Two Concrete Design Methods

Towards sustainable coal industry: Turning coal bottom ash into wealth

Although the world is gradually moving towards renewable energy resources, the coal industry will continue to be a major energy supply sector in the foreseeable future. However, by-products such as coal fly ash (CFA), coal bottom ash (CBA), and boiler slag are generated during coal combustion, and have become a significant environmental concern. There is an urgent need for transdisciplinary efforts in research, policy, and practice to reduce these by-products substantially. Many studies have focused on the environmental management and comprehensive utilization of CFA. As a comparison, less attention has been paid to CBA. Therefore, this critical review provides a holistic picture of CBA, from the generation, fundamental characteristics, environmental concerns to potential applications, and benefits analysis. Based on the fundamental characteristics, CBA can be considered as a sustainable and renewable resource with great potential to produce value-added materials. High-value applications and current research related to CBA, including construction and ceramic industry, wastewater remediation, soil amelioration, energy catalysis, valuable metals recovery, and material synthesis, are systemically presented and compared. It emphasizes the environmental and economic benefits of the sustainable applications of CBA as well. Particularly, it indicates that CBA is a promising candidate in normal, lightweight, self-compacting, and ultra-high-performance concrete, which shows a reduction in both energy consumption and greenhouse gas emissions during concrete production. This work provides new insights into the greener and sustainable applications of CBA, and it will offer a practical guide for the sustainable development of the coal industry.

Environmental Evaluation of Concrete Containing Recycled and By-Product Aggregates Based on Life Cycle Assessment

This study aims to compare the potential environmental impact of the manufacture and production of recycled and by-product aggregates based on a life cycle assessment and to evaluate the environmental impact and cost when they are used as aggregates in concrete. To this end, the six potential environmental impacts (i.e., abiotic depletion potential, global warming potential, ozone-layer depletion potential, acidification potential, photochemical ozone creation potential, and eutrophication potential) of the manufacture and production of natural sand, natural gravel, recycled aggregate, slag aggregate, bottom ash aggregate, and waste glass aggregate were compared using information from life cycle inventory databases. Additionally, the environmental impacts and cost were evaluated when these aggregates were used to replace 30% of the fine and coarse aggregates in concrete with a design strength of 24 MPa. The environmental impact of concrete that incorporated slag aggregate as the fine aggregates or bottom ash aggregate as the coarse aggregates were lower than that of concrete that incorporated natural aggregate. However, concrete that incorporated bottom ash aggregate as the fine aggregates demonstrated relatively high environmental impacts. Based on these environmental impacts, the environmental cost was found to range from 5.88 to 8.79 USD/m3.

Environmental Impact of Corn Tortilla Production: A Case Study

The research on the environmental impacts of corn-derived products has been mainly on cultivation techniques and the production of biofuels, so there is limited information on the impacts produced by the transformation of corn for human consumption. The tortilla is a millennial product derived from corn of which consumption is increasing in North America. The aim of this study is to identify the environmental hotspots of the tortilla using a life cycle assessment (LCA) approach. The process studied included only the corn–nixtamalisation–dough–tortillas production. The functional unit is one kg of tortillas packed in kraft paper. The impacts of the tortilla production process were evaluated using SimaPro 8.5.0 software, considering ReCiPe Midpoint. The production has the greatest impact in 15 of the 18 impact categories. The normalisation reveals that the most significant impacts concentrate in the categories terrestrial acidification (TA), particulate matter formation (PMF), marine ecotoxicity (MET) and fossil fuel depletion (FD). Improvements in the cultivation could mean more environmentally friendly tortilla production.