Life Cycle Assessment Studies Research Articles

Integrating ecosystem services and life cycle assessment: a framework accounting for local and global (socio-)environmental impacts

PurposeHuman activities put pressure on our natural ecosystems in various ways, such as globally through the spread of emissions or locally through the degradation of species-rich landscapes. However, life cycle assessment (LCA) studies that integrate ecosystem services (ES) are still in the minority because of intrinsic differences in data, modelling, and interpretation. This study aims to overcome these challenges by developing and testing a framework that comprehensively evaluates the (socio-)environmental impacts of human activities.MethodsLCA and ecosystem services assessment (ESA) were integrated in two different ways: (1) both methodologies run in parallel and results are combined, and (2) LCA as a driving method where ES are integrated. Because local ESA studies contain the most accurate information but will not be available for all processes in the value chain, it was necessary to advance the life cycle impact assessment method ReCiPe 2016 including three new midpoint impact categories (terrestrial provision, regulation, and cultural ES) and site-generic CFs based on the Ecosystem Services Valuation Database to account for changes in regulating, cultural and provisioning ES due to land use, for the remaining processes in the value chain. Monetary valuation is used to aggregate at the areas of protection (AoP).Results and discussionA comprehensive LCA+ES-ESA sustainability assessment framework is developed to account for local and global impacts due to human activities on three AoPs (natural resources, ecosystem quality, and human health and well-being), of which the results are expressed in monetary terms. The framework is able to visualize all benefits and burdens accounted for through the handprint/footprint approach. A simplified terrestrial case study on Scots pinewood shows the applicability of the proposed framework, resulting in a handprint (€2022 9.81E+02) which is four times larger than the footprint (€2022 2.31E+02) for 1 kg of wood produced. Challenges related to the framework such as data availability and database shortcomings (i.e., beyond land use) and ES interrelations are discussed.ConclusionWhile classical LCA studies focus more on burdens, this framework can also take into account benefits, such as the provision of ecosystem services (or the value of the functional unit of the study). Although the integration of both LCA and ESA has been increasingly explored recently, until now no framework has been available that can incorporate results from local ESA, site-specific ESA, and classical LCA studies, which is considered highly relevant to decision-making.

A comparative environmental Life Cycle Assessment study of hydrogen fuel, electricity and diesel fuel for public buses

Hydrogen fuel and electricity are energy carriers viewed as promising alternatives for the modernization and decarbonization of public bus transportation fleets. In order to choose development pathways that will lead transportation systems toward a sustainable future, the authors developed an environmental model based on the Life Cycle Assessment approach. The model tested the impact of energy carrier consumption during driving as well as the electricity origin employed to power electric buses and produce hydrogen. Energy sources such as wind, solar, waste and grid electricity were investigated. The scope of the study included the life cycles of the energy carrier and the necessary infrastructure. The results were presented from two perspectives: the total environmental impact and global warming potential. In order to create a roadmap, an original method for choosing sustainable development pathways was prepared. It was shown that the modernization of conventional bus fleets using hydrogen and electrical pathways can provide significant environmental benefits from both perspectives, but especially in terms of global warming potential. It was emphasized that attention should be paid to the use of low- and zero-emission energy sources, because their impact often strongly influenced the final environmental judgment. The energy carrier consumption also had a strong impact on the results obtained, and that is why efforts should be made to reduce it. In addition, it was confirmed that hydrogen and electricity production systems based on electricity generated by a waste-to-energy plant could be an environmentally reasonable dual solution for both sustainable waste management and meeting transport needs.

Impact of Drinking Water Treatment Process Using Life Cycle Assessment (LCA) to Minimize Environmental Impact Risk

The clean water treatment plant at DWTP is carried out with conventional treatment. The conventional water treatment process has an impact on the environment due to the clean water treatment process. Clean water treatment produces GWP and Eutrophication impacts derived from the use of chemicals and electricity. This study aims to analyze the factors causing environmental impacts arising from the clean water treatment process at the PDAM Water Treatment Plant (IPA) and determine policy priorities related to reducing environmental impacts and improving the quality of drinking water treatment at the Water Treatment Plant based on the results of LCA and AHP studies. The Life Cycle Assessment (LCA) method is a method of assessing the potential environmental impact and evaluating the environmental performance of a process on the product. Life Cycle Assessment (LCA) consists of four stages, namely determination of Goal and Scope, Life Cycle Inventory, Life Cycle Impact Assessment, and data interpretation. In research, the scope of LCA used is Gate to Gate, namely in the Coagulation, Flocculation, and Sedimentation process units. From the results of the LCA study, the potential impact of GWP of 12760.76 KgCO2-eq comes from flocculation which produces floc from the addition of chemicals. Meanwhile, the potential impact of eutrophication is 268.55 KgPO4-eq derived from mud generation. The results of the decision in reducing environmental impact at DWTP by optimizing chemicals as a top priority, then the second priority by recycling sludge, and finally making savings and energy alternatives are the last priority. Each respondent's score reached 55%, 23% and 22%. The results of the implementation of the program if implemented can reduce the impact of GWP 20079.17 kg CO2-eq and the impact of eutrophication can be reduced by 201.401 kg PO4-eq.mportant matters discussed in the paper that significantly contribute to the final result of the research may be noted here, but you have to consider, however, the limited space of the abstract.

Carbon footprint of hydrogen-powered inland shipping: Impacts and hotspots

The shipping sector is facing increasing pressure to implement clean fuels and drivetrains. Especially hydrogen-fuel cell drivetrains seem attractive. Although several studies have been conducted to assess the carbon footprint of hydrogen and its application in ships, their results remain hard to interpret and compare. Namely, it is necessary to include a variety of drivetrain solutions, and different studies are based on various assumptions and are expressed in other units. This paper addresses this problem by offering a three-step meta-review of life cycle assessment studies. First, a literature review was conducted. Second, results from the literature were harmonized to make the different analyses comparable, serving cross-examination. The entire life cycle of both the fuels and drivetrains were included. The results showed that the dominant impact was fuel use and related fuel production. And finally, life-cycle hot spots have been identified by looking at the effect of specific configurations in more detail. Hydrogen production by electrolysis powered by wind has the most negligible impact. For this ultra-low carbon pathway, the modes of hydrogen transport and the use of specific materials and components become relevant.

Establishing the effectiveness of life cycle assessment to assess the environmental impact of passenger cars using biofuels: A Review

Predictions and decisions made by legislators may be partially or wholly informed by the results of life cycle assessment studies, but the outcomes can vary significantly. This review seeks to establish whether existing life cycle assessment study results are accurate and if there are errors or deficiencies in life cycle inventory databases, chosen methodologies, or choice of life cycle assessment tool that may impact the outcome of life cycle assessment studies. The context of the work is set against the role bioethanol/gasoline blends might play in reducing the environmental impact of internal combustion engine-powered vehicles. The findings indicate inaccuracies exist and that there are various reasons for this. The accuracy of life cycle assessment results is affected by differences and inconsistencies that occur between life cycle inventory databases, the choice of life cycle inventory databases and life cycle assessment tools and because, in many cases, life cycle assessment methodology does not specify whether the biofuel content in the fuel is considered. The increase in the average age of biofuel-compatible passenger cars challenges the validity of results obtained by employing the commonly used approach based on fixed annual mileage profiles and lifetime activity. Uncertainty is a significant factor, and more attention should be paid to uncertainty analysis. Evidence shows the use of biofuels can deliver considerable environmental gains and reductions in CO2, especially in blends containing a higher percentage of biofuel.

Environmental impact assessment of red mud utilization in concrete production: a life cycle assessment study

Environmental impact assessment of red mud utilization in concrete production: a life cycle assessment study

Comparative environmental and economic life cycle assessment of phytoremediation of dredged sediment using Arundo Donax, integrated with biomass to bioenergy valorization chain

The economic and environmental life cycle assessment (LCA) was integrated into a laboratory-based experiment to evaluate the feasibility and sustainability of phytoremediation of chloride-rich marine dredged sediment, using perennial reed Arundo Donax along with biomass valorization. As a prerequisite for life cycle assessments, a baseline mathematical model was developed to estimate the yields of biomass to bioenergy valorization chain including the estimation of biomass yield per m3 sediment, bioenergy yields from valorization schemes, expected green electricity yield, and the phytoremediation time frame. This mathematical model was applied to develop a parametric life cycle inventory for two scenarios of sediment phytoremediation separately or integrated with biomass valorization, for LCA and further sensitivity and uncertainty analysis. Comparative LCA unveiled that the cost and environmental impacts of annual phytoremediation of 1m3 sediment alone or integrated with biomass valorization are much inferior to the corresponding sediment landfill as the inevitable alternative approach for sediment management. With the chloride bioaccumulation capacity of 9940 mg per kg dry biomass of A. donax, the phytoremediation of sediment with chloride concentration higher than 1650 mg/kg may not be achievable in a realistic time frame. Due to the importance of considering sediment depth and the effectiveness of the plant rooting system in estimating the performance of phytoremediation and the time frame, the volume of sediment (1m3) is a more appropriate functional unit than the surface area (ha) for LCA studies of phytoremediation. In addition, considering the volume of sediment as a functional unit retains comparability to other valorization scenarios such as sediment incorporation in cementitious matrices and management scenarios such as landfill, which are generally expressed on a volume or mass basis. Integrating biomass-derived bioenergy production into phytoremediation could offer local and global benefits in terms of economy and environment mainly due to carbon sequestration and avoiding fossil-based fuels.

Life Cycle Assessment of PLA Products: A Systematic Literature Review

The rising concerns about environmental harm and pollution create a setting for the search for better materials to produce more sustainable products. Plastic plays a crucial role in modern life and most of the commonly used are of fossil origin. Polylactic Acid (PLA) has been appointed as a more sustainable alternative, due to its origins in biodegradable raw materials. This paper aims to review scientific research, where Life Cycle Assessment (LCA) is performed on this material, in order to further understand the environmental impacts and to assess whether it is a more viable option when compared to the most commonly used plastics. A systematic literature review of 81 LCA studies focused on the LCA of PLA products was conducted. An assessment of key aspects, including the system boundaries, raw materials origin, and quantitative analysis of five environmental impact categories was performed. In this comparative analysis, in addition to presenting the results for PLA products, they are also compared with other fossil-based plastics. This leads to the conclusion that PLA has higher environmental impacts on Marine Eutrophication, Freshwater Eutrophication, and Human Toxicity, which are mainly related to the agricultural phase of growing the raw materials for PLA production. For Climate Change, Polystyrene (PS) presents the higher Greenhouse Gas (GHG) emissions, and for the Ozone Layer Depletion category, Polyethylene terephthalate (PET) presents the higher impact. PLA is a solution to replace fossil plastics. However, the use of alternative biomass sources without competition with the feed and food sector could be a key option for biobased materials production, with lower environmental and socioeconomic impacts. This will be a pathway to reduce environmental impacts in categories such as climate change, marine eutrophication, and freshwater eutrophication.

Global Development on LCA Research

Research on life cycle assessment (LCA) has been conducted over three decades. According to ISO 14040, LCA is an international standard that provides a methodology for assessing the environmental impact of products and processes. In the context of this study, research papers relevant to LCA are evaluated to conduct a bibliometric analysis of the LCA study from 2010 to 2021. The scope of this inquiry is confined to the Web of Science database of scientific papers. This analysis considers the authors' identification, type of articles, discipline, journal, citation, and bibliometric analysis components. Statistics of the most productive authors, institutions, and countries are also presented. The United States is the leading country in this field of LCA study. In addition, the word cloud and word dynamics are also evaluated. The bibliometric information is represented graphically in the bibliographic connection and co-citation network. This study will aid scholars in gaining systematic knowledge and comprehension of LCA research and its consequences.

An Environmental Impact Assessment of Largemouth Bass (Micropterus salmoides) Aquaculture in Hangzhou, China

With the rapid increase in aquaculture production, its role in food safety and nutritional security has become increasingly important, but this has also given rise to environmental problems that cannot be ignored. The largemouth bass (Micropterus salmoides) has become a widely cultivated and highly economic freshwater farmed species since it was introduced to China in 1983; however, the environmental impacts of its freshwater pond aquaculture process have not yet been elucidated. Here, life cycle assessment (LCA), a decision-making tool that can evaluate and identify environmental issues during production processes, was used to evaluate the environmental performance of the largemouth bass freshwater pond aquaculture process, and a large-scale, commercial company was selected as an example in Hangzhou, China. The results showed that the pond-farming stage and marine aquatic ecotoxicity potential (MAETP) had the largest environmental impacts on the entire aquaculture process. An environmental contribution analysis indicated that electricity (48%) and emissions (23%) were two key factors in the seed-rearing stage, and electricity (60%) and feeds (26%) were two main impact contributors in the pond-farming stage. Improvement measures based on emerging technologies in aquaculture were discussed, namely, clean energies, industrial pond farming, and intelligent feeding strategies, to help with decision making for continuous improvement in the environmental performance of largemouth bass pond farming. Moreover, suggestions for further aquaculture LCA studies in China were summarized, as they will provide a useful reference for promoting the development of China’s aquaculture LCA research and the enrichment of the world’s aquaculture life cycle inventory databases.

Embodied life cycle impacts of lightweight building methods for affordable houses in the USA: Comparison of conventional, circular, and regenerative strategies

The transition to more circular practices in the construction sector offers an alternative to linear processes that are highly polluting and wasteful. Recent life cycle assessment (LCA) studies emphasize the relevance of the end-of-life scenario, highlighting its potential for impact reduction through circular strategies. There is an urgent need to fill the knowledge gap in the LCA literature on reducing the environmental impacts of affordable housing. Whole-building LCAs of three affordable homes built using a variety of lightweight construction methods in the southern United States were conducted to examine the environmental impacts of commonly used construction solutions for single-family affordable housing in the southern US and assess the extent to potential environmental impact mitigation through the introduction of additional circular strategies or the use of regenerative materials. In addition to the conventional as-built scenario, five hypothetical scenarios were considered in this study to evaluate the influence of different end-of-life options, namely, reduced recycling rates, increased recycling or reuse rates, and substitution of conventional insulation or finish materials with equivalent options from regenerative sources. The study aims to identify further opportunities for and limits to impact mitigation. The results show that the design and construction priorities should be (1) promoting proper end-of-life strategies for metals and wood-based materials, (2) replacing non-renewable materials with renewable wood or earth materials, and (3) increasing the reuse rate of materials and diverting construction waste. The study findings will support decision-making processes concerning the design and construction of low-impact affordable single-family homes and the development and implementation of affordable housing policies and regulations, resulting in greater environmental justice and a more equitable and sustainable built environment.

A cleaner approach with magnetically assisted reactor setup over CaO-zeolite/Fe3O4 catalyst in biodiesel production: Evaluation of catalytic performance, reusability and life cycle assessment studies

This study reports the magnetic catalyst constructed by incorporating magnetite (Fe3O4) within zeolite-supported calcium oxide (CaO) in conventional and magnetic reactors for heterogeneous catalytic biodiesel production. The CaO-zeolite/Fe3O4 catalyst demonstrated remarkable characteristics, including a substantial surface area, acid-base properties, and high magnetization. These attributes enable efficient transesterification of used cooking oil (UCO) with high free fatty acid (FFA) content and facilitate the easy separation of the solid catalyst by utilizing magnetic force once the reaction is complete. In the conventional reactor, employing a 3 wt% catalyst dosage and a 5:1 methanol to oil molar ratio, the maximum biodiesel yield reached 93.64% after 240 min at 55 °C. Meanwhile, the magnetic reactor yielded a maximum biodiesel yield of 96.91% when operating for 300 min, using a 4 wt% catalyst dosage, 5:1 methanol to oil molar ratio, and maintaining a reaction temperature of 55 °C. The catalyst reusability result did not indicate an appreciable reduction in biodiesel yield in 4 cycles with the magnetic reactor. The life cycle assessment (LCA) study also revealed fewer negative effects of biodiesel production by using a magnetic reactor on the environment. The efficient utilization of CaO-zeolite/Fe3O4 catalyst in the magnetic reactor has shown great potential for industrial application.

A case study of comparative techno-economic and life cycle assessment of tap water versus household reverse osmosis-based drinking water systems in a North Indian city

Abstract Household reverse osmosis (RO)-based water purifiers have gained popularity in India due to concerns about the quality of tap water. However, the widespread adoption of these systems has significant impacts on water pricing and the environment. The objective of this study was to assess the techno-economic performance and life cycle assessment (LCA) of household RO-based water purifiers in Srinagar city of North India. Our results demonstrate that household ROs reduce the concentration of important dietary minerals such as fluoride and magnesium in drinking water by 50%. In addition, the average total water cost from a household RO is three to four times more than what is being paid for tap water. Two different scenarios were compared in LCA. The first scenario was safe drinking water from a conventional drinking water treatment plant (scenario 1), while the second scenario was water from a household RO system (scenario 2). The results showed that the environmental impacts of abiotic depletion, acidification of water bodies, eutrophication, global warming and ozone depletion in scenario 2 were higher than in scenario 1. The findings infer that water utilities should encourage citizens to rely on conventional tap water as a cheaper and environmentally friendly option compared to household ROs.

The impact of fossil jet fuel emissions at altitude on climate change: A life cycle assessment study of a long-haul flight at different time horizons

Air traffic has increased by about 60% between 2011 and 2019 and climate forcers from aviation have also increased, resulting in a strong impact on climate change. It is well established that CO2 is the largest climate forcing component connected with aviation and its impact is now well calculated and documented. However, other climate forcers such as nitrogen oxides (NO and NO2), although not considered as greenhouse gases by the Kyoto Protocol, have a significant indirect impact on climate change. Post-combustion of the most common fossil fuel, Jet A-1, results in emissions of carbon dioxide (CO2), water vapor (H2O), volatile organic compounds (VOCs), sulfate ions (SO42−), carbon monoxide (CO), nitrogen oxides (NOx) and soot. Soot and water vapor emissions can trigger the formation of contrails-cirrus. Due to differences in lifetimes, temperature, pressure, humidity, and reactivity, all these climate forcers have not the same impact on climate change. Since 80% aviation fuel is burned during the cruise phase, this paper aims to improve the environmental assessment of the altitude emissions of the Jet A-1 fossil fuel, using Life Cycle Assessment (LCA) methodology. This method is a reference for calculating the environmental impact of air transport emissions. However, when it comes to assessing the impact of emissions at altitude, LCA models only take into account the impact of CO2 on climate change. New global warming potentials (GWP) and emission indices (EI) of climate forcing components related to air traffic were therefore included in our calculations to estimate the climate impact ICC at two different time horizons. In this paper, we show that the inclusion of non-CO2 effects results in an increase in the ICC at the 100- and 20-year THs of 115% and 517%, respectively. This considerable increase illustrates the crucial role of short-lived climate forcers that may have a greater impact when a shorter time horizon of 20 years is chosen.

Life Cycle Assessment of construction materials: Methodologies, applications and future directions for sustainable decision-making

This review paper presents a comprehensive analysis of Life Cycle Assessment (LCA) methodologies applied to construction materials. It begins with an introduction highlighting the significance of LCA in the construction industry, followed by an overview of LCA principles, phases and key parameters specific to construction materials. The methodological approaches utilised in LCA, including inventory analysis, impact assessment, normalisation, allocation methods and uncertainty analysis, are discussed in detail. The paper then provides a thorough review of LCA studies on various construction materials, such as cement, concrete, steel and wood, examining their life cycle stages and environmental considerations. The review also explores recent advances in LCA for construction materials, including circular economy principles, renewable alternatives, technological innovations and policy implications. The challenges and future directions in LCA implementation for construction materials are discussed, emphasising the need for data quality, standardisation, social aspects integration and industry-research collaboration. The provides valuable insights for researchers, policymakers and industry professionals to enhance sustainability in the construction sector through informed decision-making based on LCA.

Technoeconomic and Environmental Assessment of Biomass Chemical Looping Gasification for Advanced Biofuel Production

Chemical looping gasification is a promising biomass conversion technology that could produce sustainable liquid transportation fuels on a large scale to reduce fossil fuel dependency. The current paper examines the technical, economic, and environmental performance of a biomass-to-liquid (BtL) process based on chemical looping gasification and Fischer-Tropsch synthesis. Two biomass feedstocks, i.e., pine forest residues and wheat straw, are selected for assessing the complete BtL production chain. The results of process simulations showed that both biomass types are suitable gasification feedstocks, with an overall energy efficiency of 53% and 52% for pine residues and wheat straw, respectively. The economic results show that the breakeven selling prices (BESP) are €816 and €781 per m3 for the pine forest residues and wheat straw pellets, respectively. However, if low-grade excess heat valorisation and CO2 credits are considered, the BESPs could meet or become lower than the target value of €700 per m3, making the BtL plant competitive with other biofuel plants. The CO2 avoidance cost is estimated at €74.4/tCO2 for pine residues and €61.3/tCO2 for wheat straw, when replacing fossil fuels. The results of the life cycle assessment study showed that the produced biofuels fulfil the requirements of the EU Renewable Energy Directive II, achieving the reduction in greenhouse gases emissions of up to 79% without carbon capture and storage (CCS) and up to 264% with CCS compared to fossil fuels.

Environmental impact of pavements formulated with bitumen modified with PE pyrolytic wax: A comparative life cycle assessment study

This study aimed to evaluate the environmental impacts of various bitumen modifiers on asphalt production, given its significant contribution to greenhouse gas emissions, waste generation, and the depletion of non-renewable resources. Four bitumen modifiers were compared, namely, recycled polyethylene (PE) pyrolytic wax, ethylene-vinyl acetate (EVA), recycled polypropylene (PP), and a combination of PE pyrolytic wax and PP, using the life cycle assessment method with one km of road as the functional unit. Results showed that the use of asphalt mixtures formulated with bitumen modified with PE pyrolytic wax had the lowest environmental impact, with a 5.9% decrease compared to traditional pavement. This reduction was attributed to the generation of environmental credits from pyrolysis and a decrease in the amount of virgin bitumen needed for asphalt mixture formulation. Conversely, binders modified with EVA and recycled PP had the highest environmental impact due to high maintenance requirements and environmental impacts in their corresponding additives, with 12% and 5% more impact than traditional pavement, respectively. The study further noted that overall environmental performance was highly sensitive to the amount of bitumen required and the yield of wax produced during pyrolysis, indicating the importance of carefully selecting bitumen modifiers. Based on the findings, the study recommends the use of asphalt mixtures formulated with bitumen modified with PE pyrolytic wax due to their favourable environmental performance.

Environmental sustainability of microalgae-based production systems: Roadmap and challenges towards the industrial implementation

Microalgae and cyanobacteria are a precious source for the production of biofuels/bioenergy, biomaterials and valuable biochemicals. Beyond photosynthetic CO2 conversion, microalgal systems can involve the valorisation of waste streams and the implementation of green chemistry, industrial symbiosis, and circular bioeconomy approaches. However, their sustainability is uncertain, thus their large-scale application is hindered. The numerous life cycle assessments (LCAs) performed so far are mostly based on data extrapolated from lab-scale experiments or the literature, leading to qualitative and controversial results. This paper reviews primary data-based LCA studies on microalgal pilot to industrial-scale plants. Sixteen studies satisfied the selection criteria, despite they used primary data almost exclusively for cultivation and harvesting. The outlined current status (methodology, inventory, energy performance and environmental impacts) highlighted the lack of uniformity in the applied methods and the presentation of results, as well as some lack of transparency. Nevertheless, the review concluded that electricity consumption and infrastructure are major hotspots. Therefore, the use of renewable energy for supplying the process and of sunlight for biomass photosynthesis should be preferred. The upstream processes produce large impacts. Thus, a suitable reactor, geographic location, and harvesting method should be selected. Biofuels are not competitive in most cases, but some promising multi-product biorefinery scenarios have been presented. To improve the environmental profile of microalgal high-value compounds (e.g., astaxanthin or biostimulants), co-product valorisation, waste stream utilization, renewable energy deployment, and compound productivity should be enhanced. More efforts on LCA of large-scale plants are required, especially looking at integrated biorefinery concepts, to take a crucial step towards the implementation of sustainable commercial systems.

Environmental assessment of asphalt mixtures modified with polymer coated rubber from scrap tires

Polymer coated rubber (PCR) is an engineered crumb rubber developed to address the drawbacks of regular crumb rubber in asphalt mixtures, such as the absorption of asphalt binder and premature cracking. Assessing the use of PCR using life cycle assessment (LCA) is important to evaluate whether its use lowers the environmental impact of asphalt mixtures. In LCA, the choice of allocation procedure significantly impacts the results. The cut-off method is often used in LCA studies of products containing recycled materials. The objectives of this work were to evaluate: i) if asphalt mixtures modified with PCR had lower environmental impact than mixtures modified with synthetic polymers, ii) if using more PCR decreased the environmental impact of the asphalt mixtures, iii) if the results changed by using different allocations methods, and finally, iv) if the environmental impact of asphalt mixtures changed when considering the long-term mechanical performance of the blends. In this work, the global warming potential (GWP), fossil depletion, and cumulative energy demand of one ton of asphalt mixture were calculated using the cut-off method, economic allocation, and system expansion. For the system expansion, the recovery energy in cement kilns from scrap tires was compared to burning petroleum coke or natural gas. The LCA of asphalt mixtures modified with two amounts of PCR (0.5% and 1% by weight of total mixture) compared to the synthetic polymer styrene-butadiene-styrene (SBS) was performed by including results of the experimental investigation (asphalt mixture design and mechanical testing conducted in the asphalt laboratory at Michigan State University). Results were different based on the allocation method considered. Overall, the GWP of PCR 0.5% and PCR 1% mixtures was lower than the SBS mixture, except in one case. The GWP of PCR 1% was 2% higher than the SBS mix when petroleum coke was used in the system expansion. Adding more PCR did not necessarily increase the environmental benefits. PCR 1% had a higher GWP than PCR 0.5% (2.6%, 2.7%, and 6.3% by using cut-off, economic allocation, and system expansion, respectively), except for the system expansion using natural gas as a replacement, which was 3.7% lower than the PCR 0.5%. However, the system expansion with natural gas had the lowest GWP compared to the other methods. On the contrary, the system expansion considering petroleum coke had the highest CO2eq emissions among all the methods used. The GWP of PCR 0.5% and PCR 1% was similar by using cut-off and economic allocation. As the cement industry transition to low-carbon energy, the carbon footprint associated with using scrap tires in pavements will decrease when using system expansion, while it will remain the same with the cut-off method. Considering the mechanical performance of the mixtures, the GWP for the pavement with 0.5% PCR was 8.04% lower over its service life than the synthetic polymer blend.

Utilization of phosphorus slag as fly ash replacement in low-heat Portland cement blends: Comparative study of hydration behaviors, physical properties, and life-cycle assessment

This paper presents the benefits of utilizing phosphorus slag (PS) to replace fly ash (FA) in low-heat Portland cement (LHPC) blends. After the first three days, PS exhibits worse mechanical properties and lower hydration heat compared to FA, presumably owing to its retarding effect. Meanwhile, the mechanical properties of PS are approached that of FA at 180 days. Based on the Krstulovic-Dabic (K-D) model, the Qmax values of LHPC, L75F25 (where the letters stand for the material and the numerals indicate the composition percentage), L65F35, L75P25, L65P35, and L50F25P25 are: 370.4 J/g, 312.5 J/g, 323.6 J/g, 333.3 J/g, 322.6 J/g, and 238.1 J/g, respectively. The effects of pozzolanic reaction and pore structure refinement of PS are more pronounced than that of FA, resulting in the Qmax of PS being relatively higher compared to FA. The number of gel capillaries (d < 10 nm) in L75P25 is 12% higher compared to L75F25 at 90 days. The pozzolanic reaction in FA is mainly occurred within 3 days to 28 days. However, in PS the corresponding period is from 28 days to 90 days. Furthermore, the synergistic impact between FA and PS in LHPC ternary blends is further decreased the drying shrinkage and cumulative heat, increases the H/LHPC content, and refines the pore structure. L75P25 has the lowest strength-normalized cost, which is 0.069 $/t/MPa ∼ 0.100 $/t/MPa less compared to L75F25. LHPC-FA-PS ternary blends has pronounced advantages on the strength-normalized energy consumption and carbon footprint. The strength-normalized carbon footprint and energy consumption of L50F25P25 are 1.89 kg/t/MPa and 5.57 MJ/t/MPa lower compared to L75F25, respectively.