Alternative stabilised rammed earth materials incorporating recycled waste and industrial by-products: Life cycle assessment

Alternative stabilised rammed earth materials incorporating recycled waste and industrial by-products: Durability with and without water repellent

Given increasing environmental concerns, lower energy building materials are being developed to reduce greenhouse gas emissions. The ancient technique rammed earth has been combined with modern industrial waste products to both reduce greenhouse gas emissions and reduce waste. The new rammed earth mixes have been developed using alkaline activation (sodium hydroxide) of industrial by-products: fly ash, ground granulated blast furnace slag and silica fume. This paper explores the ‘cradle-to-gate’ life cycle assessment, assessing global warming potential of these rammed earth materials, considering acquisition of raw or recycled materials and processing to final product of residential building envelope. These are compared with commonly used building envelope materials, brick veneer and cavity brickwork, and the more common rammed earth variety, cement-stabilised rammed earth. Results show that greenhouse gas emission savings can be made using these rammed earth mixes compared to the control building materials while achieving comparable or better material properties. Greenhouse gas emissions associated with the building envelope materials are reduced by more than half or one third when compared to cavity brickwork or brick veneer respectively. Following testing of the waste products in surplus in a given area, the same process could be followed for any geographic location.

Alternative stabilised rammed earth materials incorporating recycled waste and industrial by-products: A study of mechanical properties, flexure and bond strength

Although the use of a few industrial by-products as supplementary cementitious materials (SCMs) is one of the most recognized solutions to produce more durable and sustainable concrete, cost-competitive supply of such materials is of great concern, especially for a resource-scarce city like Hong Kong. In addition, several factors including the mechanical performance, transport distance and allocation of upstream impacts, can offset the environmental gain of concretes produced with such by-products. Other potential material such as volcanic ash, can be an effective alternative of industrial SCMs. However, there is a need to comprehensively demonstrate how this material can enhance the sustainability performance of the concrete industry. In this study, the greenhouse gases (GHG) emissions of using volcanic ash is evaluated and compared with its counterparts such as fly ash and ground granulated blast furnace slag in concrete production using a lifecycle assessment (LCA) technique. Based on the bottom-up approach, an industry level evaluation on GHG emission saving due to the use of different SCMs is conducted. The results show that more than 80 % lower GHG emissions are associated with volcanic ash compared to other SCMs. For the same grade of concrete, volcanic ash can reduce up to 25 % and 19 % of total GHG emissions compared to ordinary Portland cement and SCM concretes, respectively (at the product level). Considering the assumptions described in this study, the results reveal that by substituting 10–50 % industrial SCMs with volcanic ash, 11–37 % more GHG emissions can be reduced from the concrete industry in Hong Kong (at the industry level). The analysis conducted in this study would help source alternative SCMs for further promotion of sustainability in the construction industry of Hong Kong, where majority of SCMs are sourced from different countries.

Reinforcement corrosion in cement- and alternatively-stabilised rammed earth materials

Life cycle assessment (LCA) has been used to understand the carbon and energy implications of manufacturing and using cross-laminated timber (CLT), an emerging and sustainable alternative to concrete and steel. However, previous LCAs of CLT are static analyses without considering the complex interactions between the CLT manufacturing and forest systems, which are dynamic and largely affected by the variations in forest management, CLT manufacturing, and end-of-life options. This study fills this gap by developing a dynamic life-cycle modeling framework for a cradle-to-grave CLT manufacturing system across 100 years in the Southeastern United States. The framework integrates process-based simulations of CLT manufacturing and forest growth as well as Monte Carlo simulation to address uncertainty. On a 1-ha forest land basis, the net greenhouse gas (GHG) emissions range from −954 to −1445 metric tonne CO2 eq. for a high forest productivity scenario compared to −609 to −919 metric tonne CO2 eq. for a low forest productivity scenario. All scenarios showed significant GHG emissions from forest residues decay, demonstrating the strong needs to consider forest management and their dynamic impacts in LCAs of CLT or other durable wood products (DWP). The results show that using mill residues for energy recovery has lower fossil-based GHG (59%–61% reduction) than selling residues for producing DWP, but increases the net GHG emissions due to the instantaneous release of biogenic carbon in residues. In addition, the results were converted to a 1 m3 basis with a cradle-to-gate system boundary to be compared with literature. The results, 113–375 kg CO2 eq. m−3 across all scenarios for fossil-based GHG emissions, were consistent with previous studies. Those findings highlight the needs of system-level management to maximize the potential benefits of CLT. This work is an attributional LCA, but the presented results lay a foundation for future consequential LCAs for specific CLT buildings or commercial forest management systems.

As the second most used material after water and the producer of 8%–9% of anthropogenic greenhouse gas (GHG) emissions, concrete is a key target for environmental sustainability efforts. Of these efforts, a main focus has been the use of industrial byproducts as supplementary cementitious materials (SCMs) to replace some of the cement binder, the source of most of the GHG emissions from concrete production. As byproducts, these SCMs are frequently assumed to have limited or no emissions from production. Our goal is to see if this assumption should continue to drive mitigation efforts and to arrive at a clearer understanding of the contribution of SCMs to the environmental impacts of concrete. Needing further examination are: (1) how environmentally beneficial SCMs are if some of the primary process impacts are attributed to them rather than considering them waste products; (2) whether transporting SCMs creates greater environmental impacts than the materials they are replacing; and (3) whether location of primary processes that result in SCMs as well as location of concrete production creates particular burdens on lower income and minority communities. This work focuses on three of the most common industrial byproduct SCMs, namely silica fume, fly ash (FA), and ground granulated blast furnace slag (BFS), exploring both GHG and particulate matter emissions. We show that allocation of impacts from primary processes dramatically increases emissions attributed to SCMs. High levels of transportation of FA and BFS typically do not result in these SCMs having higher GHG emissions than a 95% clinker-content Portland cement. We find that SCMs may be produced in areas with low income or minority populations then used to lower GHG emissions concrete in another location. As such, beyond common environmental impact assessment methods, the role of environmental justice should be incorporated into impact assessments.

Addressing the social life cycle inventory analysis data gap: Insights from a case study of cobalt mining in the Democratic Republic of the Congo

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.

Different ways of performing a life cycle assessment (LCA) are used to assess the environmental burden of milk production. A strong connection exists between the choice between attributional LCA (ALCA) and consequential LCA (CLCA) and the choice of how to handle co-products. Insight is needed in the effect of choice on results of environmental analyses of agricultural products, such as milk. The main goal of this study was to demonstrate and compare ALCA and CLCA of an average conventional milk production system in The Netherlands. ALCA describes the pollution and resource flows within a chosen system attributed to the delivery of a specified amount of the functional unit. CLCA estimates how pollution and resource flows within a system change in response to a change in output of the functional unit. For an average Dutch conventional milk production system, an ALCA (mass and economic allocation) and a CLCA (system expansion) were performed. Impact categories included in the analyses were: land use, energy use, climate change, acidification and eutrophication. The comparison was based on four criteria: hotspot identification, comprehensibility, quality and availability of data. Total environmental burdens were lower when using CLCA compared with ALCA. Major hotspots for the different impact categories when using CLCA and ALCA were similar, but other hotspots differed in contributions, order and type. As experienced by the authors, ALCA and use of co-product allocation are difficult to comprehend for a consequential practitioner, while CLCA and system expansion are difficult to comprehend for an attributional practitioner. Literature shows concentrates used within ALCA will be more understandable for a feeding expert than the feed used within CLCA. Outcomes of CLCA are more sensitive to uncertainties compared with ALCA, due to the inclusion of market prospects. The amount of data required within CLCA is similar compared with ALCA. The main cause of these differences between ALCA and CLCA is the fact that different systems are modelled. The goal of the study or the research question to be answered defines the system under study. In general, the goal of CLCA is to assess environmental consequences of a change in demand, whereas the goal of ALCA is to assess the environmental burden of a product, assuming a status-quo situation. Nowadays, however, most LCA practitioners chose one methodology independent of their research question. This study showed it is possible to perform both ALCA (mass and economic allocation) and CLCA (system expansion) of milk. Choices of methodology, however, resulted in differences in: total quantitative outcomes, hotspots, degree of understanding and quality. We recommend LCA practitioners to better distinguish between ALCA and CLCA in applied studies to reach a higher degree of transparency. Furthermore, we recommend LCA practitioners of different research areas to perform similar case studies to address differences between ALCA and CLCA of the specific products as the outcomes might differ from our study.

Fly ash, GGBS, and silica fume based geopolymer concrete with recycled aggregates: Properties and environmental impacts

Engineering properties, sustainability performance and life cycle assessment of high strength self-compacting geopolymer concrete composites

Supplementary cementitious materials to mitigate greenhouse gas emissions from concrete: can there be too much of a good thing?

Understanding the Climate Mitigation Benefits of Product Systems: Comment on “Using Attributional Life Cycle Assessment to Estimate Climate‐Change Mitigation…”

Well-to-wheel greenhouse gas emissions of electric versus combustion vehicles from 2018 to 2030 in the US