Hybrid Life Cycle Assessment Method Research Articles

A Cleaner Pavement Preventive Maintenance Approach: Performance and Emission Impact Analysis of Slurry Surfacing Containing Electric Arc Furnace Slag

Incorporating Electric Arc Furnace Slag (EAFS) into construction materials such as hot-mix asphalt and Portland cement concrete has shown increasing wear and polishing resistance while reducing solid waste and mitigating the carbon footprint of construction engineering. Pavement surface treatment is one of the most used pavement preservation approaches. The slurry surfacing (SS) technique provides the most hot-mix asphalt-like surface texture among the surface treatment techniques. This study aimed to investigate the feasibility of using EAFS for SS by incorporating various amounts of EAFS and then analyzing the treatment's performance and the resulting carbon footprint reduction. Performance tests of SS, including the wet track abrasion test and loaded wheel test, were performed to evaluate SS's abrasion and deformation resistance. Aggregate packing degree and bonding strength based on the surface charge were also considered to understand the mechanism affecting the performance. The corresponding reduction in carbon footprint is then analyzed using the tiered hybrid life cycle assessment method to understand further the benefits of using EAFS in SS. The results revealed that mixtures incorporating EAFS could be carefully designed to perform better by increasing the packing degree and bonding strength. Also, adding EAFS into SS increased abrasion resistance by up to 18.2%, rutting resistance by up to 72.8%, and reduced the carbon footprint by up to 39.6%.

Carbon footprints of travel to World Heritage Sites: communicating climate to potential tourists through a consumption-based life-cycle assessment

ABSTRACT In this study, an input-output-based hybrid life cycle assessment method is used to calculate the carbon footprint of a tourist’s travel to sixteen United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage Sites (WHS) including direct and indirect emissions. The carbon footprint of three trip styles (budget, mid-range expenses, and high-end) is calculated for each WHS, reflecting options available to heritage tourists. This study is part of a more extensive study that created a climate communication recognition scheme (CCRS) for UNESCO WHS to communicate information about climate change to potential tourists and heritage site managers, elaborating and extending upon communication tools such as environmental product information schemes, certifications, and ecolabels. The results are intended for educational purposes and contribute to a holistic approach to carbon management in heritage tourism. The results are available online as an ArcGIS StoryMap titled Climate Footprints of Heritage Tourism.

Energy, water, and environmental impacts assessment of electricity generation in Iran

This paper uses a hybrid life cycle assessment method to assess the energy, water, and environmental impacts of high-voltage electricity generation in Iran based on Cumulative Energy Demand and ReCiPe 2016 methods. The aim is to determine the share of renewable and nonrenewable technologies in the associated impacts in order to inform policymakers about proper mitigation strategies. Assessments based on a cradle-to-gate approach showed that producing 1 kWh high-voltage electricity by Iran’s public sector is accompanied by 511 g-CO2-eq. greenhouse gas emissions, 9.52 MJ energy consumption, and 37 l water use. Natural-gas-firing single-cycle power plants (PPs), followed by natural-gas-firing combined cycle PPs, have the highest contributions to the life-cycle impacts of electricity generation in this country. Moreover, the consumption of liquid fossil fuels (diesel and heavy fuel oil) during the shortage of natural gas in cold seasons further escalates their contributions. The share of wind and hydropower plants in the resulting impacts was trivial by comparison. Findings suggested that an adequate supply of PPs with natural gas during clod seasons can partly lower water and environmental impacts of high-voltage electricity generation, but increasing the share of renewables in the electricity mix can considerably reduce most energy, water, and environment-related impacts.

Recent advances in carbon footprint studies of urban ecosystems: overview, application, and future challenges

Urban ecosystems are complex systems with anthropogenic features that generate considerable CO2 emissions, which contributes to global climate change. Quantitative estimates of the carbon footprint of urban ecosystems are crucial for developing low-carbon development policies to mitigate climate change. Herein, we reviewed more than 195 urban carbon footprint and carbon footprint related studies, collated the recent progress in carbon footprint calculation methods and research applications of the urban ecosystem carbon footprint, analyzed the research applications of the carbon footprint of different cities, and focused on the need to study the urban ecosystem carbon footprint from a holistic perspective. Specifically, we aimed to: (i) compare the strengths and weaknesses of five existing carbon footprint calculation methods [life cycle assessment, input–output analysis, hybrid life cycle assessment, carbon footprint calculator, and Intergovernmental Panel on Climate Change (IPCC)]; (ii) analyze the status of current research on the carbon footprint of different urban subregions based on different features; and (iii) highlight new methods and areas of research on the carbon footprint of future urban ecosystems. Not all carbon footprint accounting methods are applicable to the carbon footprint determination of urban ecosystems; although the IPCC method is more widely used than the others, the hybrid life cycle assessment method is more accurate. With the emergence of new science and technology, quantitative methods to calculate the carbon footprint of urban ecosystems have evolved, becoming more accurate. Further development of new technologies, such as big data and artificial intelligence, to assess the carbon footprint of urban ecosystems is anticipated to help address the emerging challenges in urban ecosystem research effectively to achieve carbon neutrality and urban sustainability under global change.

Spatial disparity of life-cycle greenhouse gas emissions from corn straw-based bioenergy production in China

Crop straw can be converted into bioenergy through various conversion pathways. Assessing the spatial disparity of greenhouse gas (GHG) emissions under different bioenergy conversion pathways could support region-specific policy decisions. This study assessed GHG emissions of seven corn straw-based bioenergy conversion pathways across 30 provinces in China, using a hybrid life-cycle assessment method based on a multi-regional input–output model. The results showed that, due to spatial disparity of economic supply chains, life-cycle GHG emissions of seven bioenergy conversion pathways clearly differed across 30 provinces and ranged within 82–439 kg CO2-eq per tonne of fresh corn straw with 80% moisture. Most of the bioenergy conversion pathways yielded GHG mitigation benefits across 30 provinces, except for electricity through biogas burning pathway in 3 provinces and bio-natural gas pathway in 28 provinces. Additionally, due to the spatial teleconnection of economic supply chains, bioenergy production occurring in one province could lead to GHG emissions in other provinces. The highest interprovincial embodied GHG emissions primarily occurred in Shandong. In 2012, the maximum GHG mitigation potential from corn straw-based bioenergy using straw burnt in field and abandoned amounted to 253 million tonne CO2-eq in China and interprovincial embodied GHG emissions amounted to 1.8 million tonne CO2-eq in Shandong. The findings support region-specific policymaking in the selection of suitable corn straw-based bioenergy conversion pathways and national policies for the promotion of interprovincial collaboration to reduce bioenergy-related GHG emissions.

Estimating carbon emissions from road use, maintenance and rehabilitation through a hybrid life cycle assessment approach – A case study

Road infrastructure is an important source of carbon emissions. To estimate the carbon emissions of roads, life cycle assessment (LCA) methods are widely used. Due to budget constraints, road maintenance and rehabilitation (M&R) is preferred by road agencies over new construction. However, existing LCA studies on roads have limited considerations on the emissions from the use and M&R phases. This study aims to propose and illustrate a structured hybrid LCA approach that can be adopted by road agencies to evaluate carbon emissions of the use and M&R phases of roads. A path exchange LCA method and a tiered hybrid LCA method are integrated in the proposed approach. To illustrate the proposed approach, a case study of a road network in Western Australia is conducted, which includes 17,764 road segments. The results show that from 2017 to 2026, the GWP of use and M&R phases is increased from 467.8 t CO2-e/km to 589.5 t CO2-e/km·with an increasing trend. The use phase has much higher global warming potential than the M&R phase during the service life of roads. The results are the most sensitive to annual average daily traffic (AADT). In addition, heavy traffic roads in the metropolitan area and freeways with AADT higher than 20,000 are identified to be the most carbon intensive. The proposed approach is believed to have better accuracy when compared to a process-based approach and a tiered approach, which provide the results of 128.6–164.4 t CO2-e/km and 468.0–608.9 t CO2-e/km, respectively. The results can provide implications for road authorities to evaluate their priorities when allocating limited M&R funds to achieve sustainable objectives.

Research on Carbon Emissions of Electric Vehicles throughout the Life Cycle Assessment Taking into Vehicle Weight and Grid Mix Composition

To study the impact of the promotion of electric vehicles on carbon emissions in China, the full life carbon emissions of electric vehicles are studied on the basis of considering such factors as vehicle weight and grid mix composition, and fuel vehicles are added for comparison. In this paper, we collect data for 34 domestic electric vehicles, and linear regression analysis is used to model the relationship between vehicle weight and energy consumption. Then, a Hybrid Life Cycle Assessment method is used to establish the life cycle carbon emission calculation model for electric vehicles and fuel vehicles. Finally, the life cycle carbon emissions of electric vehicles and fuel vehicles under different electrical energy structures are discussed using scenario analysis. The results show that under the current grid mix composition in China, the carbon emissions of electric vehicles of the same vehicle weight class are 24% to 31% higher than that of fuel vehicles. As the proportion of clean energy in the grid mix composition increases, the advantages of electric vehicles to reduce carbon emissions will gradually emerge.

Hybrid Life Cycle Assessment of Greenhouse Gas Emissions in Australian Built Environment across Scales

As the built environment is being the main contributor to global greenhouse gas (GHG) emissions, a growing number of studies are conducted to assess the life cycle GHG emissions of individual buildings. However, the precinct-scale assessment incorporating infrastructure and occupants’ activities is often limited. This study applied a newly developed hybridised Australian life cycle inventory (LCI) database to assess the life cycle GHG emissions of Australian built environment across scales starting from building products, via buildings to a precinct. This coherent bottom-up assessment framework ensured the consistency of system boundaries as well as the completeness, transparency, and comparability of data. The precinct-scale life cycle GHG emissions were comprised of embodied emissions, operational emissions and transport emissions, which took up 18%, 48% and 34% of the life cycle emissions, respectively. Major emissions hotspots of each category were identified, and accordingly, twelve commonly applied emission reduction measures, including the deployment of solar photovoltaic, the use of electric cars and energy efficient appliances, the replacement of carbon-intensive construction materials and the change of occupants’ behaviours, were suggested and quantified. With mature technologies status in quo and minimal system disruption, the scenarios demonstrated an achievable emissions reduction potential of 26%, and the most effective measures were related to operational and transport emissions. Meanwhile, the results from hybrid life cycle assessment (LCA) were compared with the results obtained by conventional process-based LCA to demonstrate the comprehensiveness of hybrid LCA method and to elaborate how the results were influenced by applying different LCA approaches. This comparison concluded the use of hybrid LCA not only resulted in higher GHG emissions for each category, but the distribution of emissions among them was also altered. This could potentially change the prioritised emission reduction areas and the most significant impacts were seen on embodied emissions. On average, the embodied emissions from the hybrid analysis was 26% higher than the corresponding process-based analysis. This ratio was reduced to 6% and 16%, respectively, for operational and transport emissions. The significance of this study is multi-faceted. For LCA researchers and practitioners, this study expands the accessibility of hybrid LCA by developing and applying a pre-compiled hybrid LCI database; for city planners, developers and architects, it implies the impact of precinct morphology and renewable energy on precincts' GHG emissions; for construction managers and building product manufacturers, the selection of building materials is relevant; and for occupants, the suggestions on behaviour change become valuable.

Hybrid life cycle assessment of greenhouse gas emissions from cement, concrete and geopolymer concrete in Australia

Concrete is the second most used material after water and the production of cement is responsible for 5–8% of global carbon dioxide emissions. The development of low-carbon concretes is pursued worldwide to help the construction industry make its contribution to decarbonising the built environment and achieving carbon reduction targets agreed under the Paris Climate Agreement. However, there is uncertainty around the actual amount of greenhouse gas emissions that can be avoided by employing alternative types of concrete. This study quantifies the carbon footprint intensities of Australian cement and concrete production, including ordinary Portland cement, standard ordinary Portland cement concrete, blended cement-based concrete and geopolymer concrete production. For the first time, an input-output based hybrid life-cycle assessment method is used for these products. The main goal of this paper is therefore to make a methodological comparison between process-based and hybrid life cycle assessment using the Australian cement and concrete production as a case study. A comparison with published results from process-based life-cycle inventories as well as a decomposition of results into product categories is provided. The hybrid life cycle assessment resulted in higher greenhouse gas emissions for ordinary Portland cement and all types of concrete due to the methodology incorporating an economy-wide system boundary, which includes the emissions from upstream processes. For geopolymer concrete in particular, the results were also dependent on the method applied for allocating greenhouse gas emissions from fly ash and slag. The findings from this study are likely to inform the development of strategies and policies aimed at greenhouse gas reduction in the cement and concrete industries.

Does a battery-electric truck make a difference? – Life cycle emissions, costs, and externality analysis of alternative fuel-powered Class 8 heavy-duty trucks in the United States

Attempting to gain insights from how alternative fuel technologies employed in heavy-duty trucks (HDTs) differ with respect to their life-cycle emissions, costs, and externalities presents an important opportunity to develop a more holistic overall analysis of future HDTs. To this end, this study uses a hybrid life-cycle assessment method to analyze and compare alternative fuel-powered Class 8 HDTs. To account for the uncertainty in the data a Monte Carlo simulation is also applied. The HDTs considered in this analysis (biodiesel (B20), compressed natural gas (CNG), hybrid, and BE HDTs) are compared to the diesel HDT (conventional HDT). The results show that BE HDTs outperform all other types of trucks overall, despite their incremental costs and electricity generation-related emissions. Furthermore, if such a BE truck were to run on electricity generated in the Northeast Power Coordinating Council (NPCC) NERC region, fuel-consumption related GHGs emissions from BE HDTs could decrease by as much as 63 percent. It has also been found that, although there is a slight difference between the life-cycle costs (LCCs) of conventional HDTs and CNG-powered HDTs, the latter emits 33% more GHGs than the former. Moreover, this study concludes that CNG trucks yield no improvements in either HDT's life-cycle environmental impacts or LCCs compared to their conventional counterparts. Providing that electricity is generated from renewable energy sources, the use of BE trucks would significantly improve the life-cycle performance of a truck as well as ambient air quality.

Using a hybrid LCA method to evaluate the sustainability of sediment remediation at the London Olympic Park

Abstract Remediation operations may have a wide range of environmental, social and economic impacts not only within the physical boundary of a contaminated site and over the operational period, but also across geophysical boundaries and beyond project life cycle. Life cycle assessment (LCA) has been increasingly used by both researchers and industrial practitioners in the ongoing green and sustainable remediation movement. This paper proposes a new hybrid-LCA method. In comparison with most remediation LCA studies in literature, the proposed approach offers several advantages by: 1) expanding the system boundary and reduces truncation errors; 2) incorporating consequential benefits (i.e. tertiary impact) of remediation; and 3) covering social and economic impact in addition to environmental impact. The hybrid LCA method is built on the 123 sector input–output analytical table and environmental account for the UK. The model was augmented with additional socioeconomic data (e.g. employment, occupational health and safety) to measure social and economic impact indicators. A sediment remediation project at the London Olympic Park site was examined using this method. The hybrid LCA was found to capture an additional 32% of secondary impact in soil washing, and 8% of secondary impact in landfilling. The tertiary impact was found to be over twice the primary plus secondary impact in soil washing, and nearly 80% of the primary plus secondary impact in landfilling. The quantitative social and economic impact assessment results also provided useful information for holistic decision making, balancing project costs with social and economic benefits.

Pollutants generated by cement production in China, their impacts, and the potential for environmental improvement

A hybrid life-cycle assessment method was performed on national and provincial statistics to study pollutants generated by the cement industry in China, the impacts of these pollutants, and the potential for environmental improvement. Results showed that the key factors that contribute to overall environmental burden are the direct emissions of nitrogen oxides (NOx), particulates, and carbon dioxide (CO2) into the atmosphere, as well as the use of coal during cement production. The amounts of CO2, sulfur dioxide (SO2), NOx, and particulates generated by the cement industry in China in 2009 were approximately 1.11 billion, 0.53 million, 2.10 million, and 3.60 million tons respectively, which accounted for approximately 14.8%, 2.4%, 12.3%, and 26.2% of the national CO2, SO2, NOx, and particulate emissions, respectively. Effective approaches to reduce the environmental impacts of the cement industry include optimizing the industrial structure in cement production, improving consumption efficiency of energy and raw materials in cement production, using industrial waste and by-products instead of limestone, decreasing cement export, and promoting electricity recovery technologies in the cement industry.

The carbon payback of micro-generation: An integrated hybrid input–output approach

Feed-in Tariffs (FiTs) in the UK have been introduced to stimulate growth in small-scale renewables such as photovoltaics and micro-wind. They form one of the UK’s key policies to decarbonise electricity by 2030. However, the evidence used to inform the policy was predominantly related to costs, capacity and deployment; not contribution to meeting decarbonisation targets. This paper employs an integrated hybrid lifecycle assessment method, which overcomes boundary limitations of traditional process-based assessments, to measure the full lifecycle emissions of solar PV and micro-wind technologies eligible under FiTs. Environmental assessments of policies often do not take account of the lifecycle emissions of technologies, therefore underestimating their emissions contribution and overestimating the success of policies towards decarbonisation targets. Considering the full lifecycle emissions, the paper assesses the effectiveness of FiTs for driving the UK’s low carbon transition. The results demonstrate that, while there is still significant variation and uncertainty with such estimates, even with the most conservative figures, both the technologies can offer substantial emission savings compared to fossil fuel alternatives when installed in suitable locations. However, the renewable resource of installation sites is critical to the carbon intensity that the technologies can offer. Under a poor renewable resource their impacts can be as high as fossil fuels alternatives. As FiTs makes no distinction between installation sites this should form part of the assessment of funding. Finally, despite their potential for carbon reduction, with the full lifecycle of the considered technologies taken into account, a target of 50gCO2e/kWh is not possible with the current technology generation efficiencies. The paper concludes that a complete re-assessment of the role of technologies in the decarbonisation of electricity is required to take into account the full lifecycle impacts to gain a more realistic picture of the mitigation potential.

Assessment of the embodied carbon in precast concrete wall panels using a hybrid life cycle assessment approach in Malaysia

Abstract There is currently growing interest in quantifying the direct and indirect carbon emissions embodied in construction materials and their components production. Previous research shows that indirect emission could be higher than direct emission for energy intensity materials such as cement and steel reinforcement. Quantifying direct emissions alone would underestimate the carbon emissions associated with a material and in turn its environmental impact. The assessment of indirect emissions is a challenging task involving upstream processes of material production. This paper investigates the existing literature on the quantification of embodied carbon by both direct and indirect emissions as well as demonstrating the application of a hybrid life cycle assessment method in building construction. The focus of this paper is the Malaysian context however the principles apply universally. A typical 2-storey residential building has been investigated to determine the total carbon emissions when comparing two construction techniques: conventionally reinforced concrete and precast concrete panels. This paper demonstrates the application of hybrid life cycle assessment by expanding the boundaries of process methods and reducing the sensitivities of I–O life cycle assessment to the raw material price fluctuation for product manufacturing.

Hybrid life cycle assessment comparison of colloidal silica and cement grouted soil barrier remediation technologies

Site remediation involves balancing numerous costs and benefits but often neglects the environmental impacts over the entire project life cycle. Life cycle assessment (LCA) offers a framework for inclusion of global environmental “systems-level” decision metrics in combination with technological and cost analysis. We compare colloidal silica (CS) and cement grouted soil barrier remediation technologies for soils affected by low level radionuclides at a U.S. Superfund site using hybrid LCA methods. CS is a new, high performance grouting material installed using permeation grouting techniques. Cement, a more traditional grouting material, is typically installed using jet grouting techniques. Life cycle impacts were evaluated using the US EPA TRACI 2 model. Results show the highest life cycle environmental impacts for the CS barrier occur during materials production and transportation to the site. In general, the life cycle impacts for the cement barrier were dominated by materials production; however, in the extreme scenario the life cycle impacts were dominated by truck transportation of spoils to a distant, off-site radioactive waste facility.It is only in the extreme scenario tested in which soils are transported by truck (Option 2) that spoils waste transport dominates LCIA results. Life cycle environmental impacts for both grout barriers were most sensitive to resource input requirements for manufacturing volumes and transportation. Uncertainty associated with the efficacy of new technology such as CS over its required design life indicates that barrier replacement could increase its life cycle environmental impact above that of the cement barrier.

Carbon emission reduction potential of a typical household biogas system in rural China

Given the rising expectations for the substitution of fossil energy with renewable energy as one of the solutions to cope with climate change, the carbon emission reduction potential of possible solutions should be evaluated in a holistic and systematic way. In this paper, a systematic account of carbon emission reduction potential was conducted for a typical household biogas system with a digester volume of 8 m3, using a hybrid life-cycle assessment method. Using a 20 year operation scenario, the total life cycle CO2 emission of this family-size biogas utilization system is 2.60 tons, i.e., 0.02 kg CO2/MJ, of which 98.46% is attributed to indirect emissions from building materials and labor inputs. Considering the carbon emission savings due to energy and fertilizer substitution, the annual CO2 emission reduction potential is 1.25 tons for the biogas system that is under consideration. Consequently, such rural household biogas systems should be operated for at least 1.78 years to achieve a positive reduction benefit, i.e., cumulative CO2 emission savings could offset the life-cycle-related CO2 emissions. The results also indicate that long-term, stable running and maintenance are key points to maximize the benefits of household biogas as an effective approach for carbon emission abatement in the rural areas of China.

Evaluating the environmental performance of a university

An increasing number of organisations are moving towards assessing and reporting their environmental performance in a supply-chain context. Not only are such “footprint”-type assessments seen as more rigorous than sustainability reports created in-house, they also offer more abatement options than assessments limited to an organisation’s premises. Hybrid life-cycle assessment methods combining input-output analysis and process analysis are ideally suited to enumerate organisational footprints, because they were developed to enable overall complete results whilst being application-specific. We apply one of these hybrid methods, the Path Exchange Method to the task of planning for a sustainable campus at the University of Sydney in Australia. We show how this method can be used by an environmental or procurement officer for exploring environmental performance and abatement options across supply chains. We also show how parts of an organisation, for example University faculties, can be assessed and compared against each other. Whilst tools like ones used in this work enable quantitative decision support for procurement and operations policies, it takes staff awareness, engagement and training to successfully put such tools into practice.

The Path Exchange Method for Hybrid LCA

Hybrid techniques for Life-Cycle Assessment (LCA) provide a way of combining the accuracy of process analysis and the completeness of input-output analysis. A number of methods have been suggested to implement a hybrid LCA in practice, with the main challenge being the integration of specific process data with an overarching input-output system. In this work we present a new hybrid LCA method which works at the finest input-output level of detail: structural paths. This new Path Exchange method avoids double-counting and system disturbance just as previous hybrid LCA methods, but instead of a large LCA database it requires only a minimum of external information on those structural paths that are to be represented by process data.

Hybrid Life-Cycle Inventory for Road Construction and Use

Life-cycle assessment (LCA) is a technique that is used worldwide by clients and their design team to assess the impact of their projects on the environment. The main advantage of LCA is in supporting decision making with quantitative data. LCA inventories can be either fully developed or streamlined. Fully developed LCAs are time-consuming and costly to prepare. Streamlined LCAs can be used as an effective decision-making tool when considering environmental performance during the design process, but with a loss of inventory completeness. Acknowledging the advantages and disadvantages of both types of LCA, this paper proposes a hybrid LCA method that uses input-output data to fill in those gaps routinely left in conventional LCA inventories. The developed hybrid LCA method is demonstrated using a life-cycle energy study of eight different road designs, including vehicle manufacture, maintenance, replacement, and operation. It was found that the road construction process was initially the most important, but in the long run the manufacture, use, and maintenance of vehicles using the road (which are an inevitable consequence of road construction) became paramount.

A hybrid life cycle assessment method for construction

Life cycle assessments (LCAs) are used to evaluate the environmental impacts attributable to products and processes. For construction projects, LCAs can be used to assess the pollution associated with the manufacture of building materials for the construction process. Despite the reliability of traditional LCA data, many upstream processes are excluded, which adversely affects overall reliability. Input-output analysis is systemically complete, but is subject to inherent errors when applied to the LCA of specific products. Analysis of an input-output LCA model provides a basis for more informed decision making regarding processes which can be ignored during the collection of traditional LCA data. This paper proposes a hybrid LCA method for construction in which national input-output data fill those ‘gaps’ not accounted for by traditional LCA data. Regardless of the level of detail at which data are collected, LCAs can now be performed at similar overall levels of framework completeness.