BIBECHANA Vol. 20, No. 3, December 2023, 326–338 ISSN 2091-0762 (Print), 2382-5340 (Online) Journal homepage: http://nepjol.info/index.php/BIBECHANA Publisher:Dept. of Phys., Mahendra Morang A. M. Campus (Tribhuvan University)Biratnagar Comprehensive review of LCA studies in Civil Engineering Ishwor Thapa1, Nirmal Prasad Baral2, Krishna Raj Adhikari3,∗ 1Department of Civil Engineering, Sharda University, Greater Noida, India 2Department of Civil Engineering, IOE Pashchimanchal Campus, Pokhara, Nepal 3IOE Pashchimanchal Campus, Pokhara, Nepal ∗Corresponding author. Email: adhikari.krishnaraj@gmail.com Abstract This review explores the application of Life Cycle Assessment (LCA) within the domain of civil engineering, aiming to provide a comprehensive overview of current research, method- ologies, challenges, and future trends. LCA serves as a pivotal tool for assessing the environ- mental impact of infrastructure projects, yet gaps persist in its integration with socioeconomic dimensions, regional considerations, and dynamic modeling. By analyzing existing literature and scholarly discussions, this review identifies research gaps and proposes directions for en- hancing the applicability and effectiveness of LCA in civil engineering. Moreover, it examines future trends such as the integration of advanced technologies, stakeholder engagement, and policy implementation, which are poised to shape the landscape of LCA practices in the civil engineering sector. Ultimately, this review paper contributes to the understanding of LCA’s potential to drive sustainable decision-making in infrastructure development, paving the way for more informed and environmentally conscious practices. Keywords Life Cycle Assessment, Civil Engineering, Environment, Indicator, Building, Road. Article information Manuscript received: September 12, 2023; Accepted: September 27, 2023 DOI https://doi.org/10.3126/bibechana.v20i3.58552 This work is licensed under the Creative Commons CC BY-NC License. https://creativecommons. org/licenses/by-nc/4.0/ 1 Introduction The field of civil engineering has witnessed a grow- ing emphasis on sustainable practices, driven by the need to address the environmental impacts of construction and infrastructure projects. In this context, LCA has emerged as a powerful tool for evaluating the comprehensive environmental impli- cations of buildings and infrastructure throughout their entire life cycle. LCA assesses the environ- mental burdens associated with each phase of a project, from raw material extraction to construc- tion, operation, and end-of-life scenarios. LCA is particularly relevant in the construction sector, which significantly contributes to energy consump- tion, resource depletion, and greenhouse gas emis- sions. 326 http://nepjol.info/index.php/BIBECHANA adhikari.krishnaraj@gmail.com https://doi.org/10.3126/bibechana.v20i3.58552 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ Ishwor Thapa et al./ BIBECHANA 20 (2023) 326-338 327 1.1 Historical Development The historical development of the LCA can be di- vided into distinct periods. The years 1970 to 1990 marked the "Decades of Conception," during which early studies emerged, addressing environmental concerns such as energy efficiency, pollution control, and waste management. The scope of analysis ex- panded to include resource requirements and waste flows, with pioneering studies on beverage contain- ers conducted by the Midwest Research Institute and Basler Hofman. Interest waned briefly, but by the early 1980s, it surged. The period from 1990 to 2000 saw the "Decade of Standardization," charac- terized by coordinated efforts through organizations such as SETAC and ISO to create a framework and terminology for LCA. This era also saw the integra- tion of LCA into policy documents and the emer- gence of impact assessment methods. The following decade, 2000 to 2010, was labeled the "Decade of Elaboration." Diverse LCA methods were explored, ranging from economic and social impacts to dy- namic and risk-based assessments. The field has expanded to cover not only environmental aspects but also societal and economic dimensions. The future (2010-2030) was anticipated as the "Decade of Life Cycle Sustainability Analysis," emphasizing a broader approach encompassing environmental, economic, and social indicators and spanning vari- ous levels of analysis from product to economy-wide assessments. This phase of development aims to ad- dress complex sustainability challenges through an integrated and transdisciplinary framework [1]. 1.2 Need of LCA in Civil Engineering The 2030 Agenda’s 17 Sustainable Development Goals (SDGs) were adopted by global leaders in January 2016. Concurrently, the Paris Agreement emerged from COP21 in November 2016, uniting countries to limit global temperature rise below 2 degrees Celsius. By April 2018, 175 parties had ratified the agreement, with 10 developing nations outlining climate change response plans. Climate change disregards borders, as evidenced by rising greenhouse gas emissions impacting weather pat- terns and sea levels [2]. A distinct SDG targets ur- gent climate action. Life cycle assessment aids sus- tainability experts, designers, and engineers in eval- uating products and systems alongside alternatives. To ensure unbiased comparability, the International Organization for Standardization (ISO) established global benchmarks, with the European Committee for Standardization (CEN) enhancing assessments for specific domains such as construction materials. A new CEN standard under development focuses on sustainability assessment methodologies for civil engineering projects [3]. This article provides an in-depth overview of the latest developments in Life Cycle Assessment (LCA) within civil engineering. This section cov- ers the tools used for analysis and the databases containing life cycle inventory (LCI) data. The ar- ticle also includes constructive criticisms addressing both the limitations of LCA and the practical chal- lenges that have arisen. The main objective of this study is to enhance our understanding of how LCA is applied in civil engineering. This, in turn, encour- ages the use of LCA as a tool for making informed decisions in managing infrastructure projects. Fur- thermore, this article aims to establish new criteria for designing with the environment in mind. 2 BASIC FRAMEWORK OF THE LCA Life Cycle Assessment (LCA) is a standardized ap- proach used to systematically analyze the environ- mental impacts of a product or service from its in- ception to its functional end. It encompasses stages such as raw material acquisition, production, us- age, maintenance, and end-of-life. These impacts include resource depletion, human health, and eco- logical well-being [4]. Despite its current applica- tion in various industries with diverse methodolo- gies, LCA’s origins date back to the 1970s. While ISO standards such as 14040 and 14044 provide guidance, they lack practical specifics [5]. 2.1 Phases of LCA Life Cycle Assessment (LCA) consists of four dis- tinct phases. The first phase involves defining the goal and scope of the assessment and setting the boundaries and objectives. In the second phase, the life cycle inventory (LCI) is compiled, where all relevant data on inputs, outputs, and processes within the system boundary are collected. The third phase, known as life cycle impact assessment (LCIA), evaluates the potential environmental im- pacts of the identified inputs and outputs. Finally, in the fourth phase, the results are interpreted, providing meaningful conclusions and recommen- dations based on the assessment’s goals and find- ings [6]. The important phases involved in LCA in civil engineering and other important issues are discussed below. Figure 1 below shows the LCA framework. Goal and Scope The LCA process begins by defining the goal and scope, which are crucial for selecting method- ology and categories. Clear articulation of the study’s scope, purpose, and assumptions, includ- ing lifecycle phases, future scenarios, and product components is pivotal. This step, which is manda- tory in each LCA study, significantly shapes its direction and ensures transparent communication Ishwor Thapa et al./ BIBECHANA 20 (2023) 326-338 328 post-study. The scope involves setting the system boundary and level of detail, both influenced by the intended LCA result use and the subject un- der examination. The scope of LCA varies widely based on its goal, making it essential and variable across cases [7]. Life Cycle Inventory The Life Cycle Inventory (LCI) involves track- ing the inputs and outputs related to a product, requiring extensive regional and global data. The process considers energy and raw materials as in- puts, and environmental emissions such as gases, liquids, and solids as outputs. Gathering data for energy, transportation, materials, and waste from sources such as factories, governments, and scien- tific journals is essential. LCI analysis compiles input/output data within the system boundary, tailored to the study’s goal. Specific case data or general databases such as Ecoinvent can be used [8]. Various specialized LCA tools and software are available for conducting LCAs with different levels of detail. Life Cycle Impact Assessment (LCIA) The Life Cycle Impact Assessment (LCIA) serves to evaluate the life cycle inventory outcomes of an analyzed system. In this process, the vari- ous outputs obtained from the Life Cycle Inventory (LCI) are adjusted by a factor based on the unit of measurement. This adjustment assigns the out- puts to specific impact categories such as global warming, land use, water use, acidification, and eutrophication. This step is referred to as "charac- terization." The software provides predefined LCI methods for this purpose. The quantified impact re- sulting from characterization can then be compared with a reference value, known as "normalization." In addition, quantified impacts can be given signif- icance values, unique to each impact category, for the calculation of a single consolidated outcome. This process is termed "weighting." These signifi- cance values are determined on the basis of factors including economic, political, and social considera- tions [6]. Interpretation Interpretation in LCA refines and explains the multitude of results to derive meaningful conclu- sions. Interpretation amalgamates inventory anal- ysis and impact assessment findings coherently with a predetermined goal and scope. This phase unveils potential limitations, drawbacks, and uncertainties [6]. Summarizing and discussing LCI and LCIA re- sults forms the interpretation stage. It leads to con- clusions, recommendations, and decision-making aligned with the defined goal and scope. Multi- criteria analysis (MCA) can yield a single weighted outcome, overcoming the need for separate results from each impact category. Employing sensitivity analysis reveals if uncertain inputs significantly in- fluence outcomes, possibly necessitating a more ex- tensive inventory analysis [9]. 2.2 Different Life Cycle Models for LCA To assess a product’s life cycle, understanding its stages is essential. The life cycle typically involves five phases: raw material extraction, manufactur- ing and processing, transportation, usage and retail and waste disposal. Various life cycle models exist, with four common ones: Cradle-to-grave analyzes impact across all five steps, whereas Cradle-to-gate assesses until factory exit. Cradle-to-cradle inte- grates recycling, closing the loop, whereas Gate- to-gate focuses on specific value-added processes. Environmental Product Declarations (EPDs) cer- tify LCA findings, and there is a specialized Well- to-Wheel approach for transport fuels and vehicles, ensuring precision in emissions and energy calcula- tions [3]. 2.3 LCA Tools and Databases Licensed software tools for LCA, notably GaBi, and SimaPro, utilize databases such as GaBi, Ecoin- vent, ELCD, U.S. LCI, IDEA, and Input-Output (I-O) for comprehensive analysis. BEDEC-ITeC fo- cuses on construction with energy, CO2, and pric- ing data[8]. Comparative reviews of construction- oriented databases highlight Ecoinvent and GaBi as superior, due to qualitative aspects. Ecochain, oneclicklca and openLCA are some other alterna- tive LCA tools. Limited free databases prompt re- liance on licensed options, hindering wider LCA ap- plication [10]. Accessible databases are essential; their absence restricts LCA studies to experts us- ing licensed software, limiting its broad adoption. Table 1 below shows the advantages and disadvan- tages of the LCA tools and database. In summary, LCA tools offer valuable capa- bilities for assessing the environmental impacts of products and processes. However, their cost, complexity, and dependence on databases can limit their widespread adoption, particularly among smaller organizations and those with limited exper- tise in LCA methodology. Accessible and current databases are crucial for accurate and meaningful LCA studies. Figure 2 shows the cost optimization process through LCA using different LCA tools and a database. Ishwor Thapa et al./ BIBECHANA 20 (2023) 326-338 329 Table 1: Advantages and Disadvantages of LCA Tools and Databases Advantages Disadvantages 1.Comprehensive Analysis 1.Cost 2.Qualitative Aspects 2.Limited Free Database 3.Construction Focus 3.Complexity 4.Alternative Options 4. Database Dependence 5.Resource Intensive 6.Data Availability 7.Subjectivity 8.Constant Updates Figure 1: LCA Framework. Figure 2: Cost Optimization through Life cycle Cost analysis. 3 Current Practice of LCA in Civil Engi- neering In the current practice of Life Cycle Assessment (LCA) in Civil Engineering, the focus is on eval- uating the environmental impacts of infrastructure projects from cradle to grave. LCA considers the entire life cycle of a structure, including raw ma- terial extraction, construction, operation, mainte- nance, and eventual demolition or disposal. Ad- vanced software tools and databases are used to model and analyze the various inputs, outputs, and environmental burdens associated with each phase. This aids engineers in making informed decisions to minimize resource consumption, energy use, emis- sions, and waste generation, ultimately leading to more sustainable and environmentally conscious de- sign and construction practices. In this review, only the structural, geotechnical, highways and con- struction material domains of civil engineering will be discussed. 3.1 Structural Engineering In the current practice of Life Cycle Assessment (LCA) in the field of Structural Engineering, the emphasis is on assessing the environmental impacts of building and infrastructure systems. This in- volves analyzing the complete life cycle of struc- tures, considering factors such as material selec- tion, construction methods, operational energy use, and end-of-life scenarios. Engineers use specialized software and databases to quantify the environmen- tal burdens associated with different structural op- tions. Majid Bahramian & Kaan Yetilmezsoy con- ducted a two-decade study on the development of life cycle assessment of the building industry from 1995 to 2018 [11]. The analysis reveals that there was a greater emphasis on studying shorter build- ings (1 to 5 floors) compared to taller ones (5 or more floors) in terms of life cycle assessment. Stud- ies on shorter buildings, mainly residential, were about twice as numerous as those on taller build- ings, where commercial structures garnered more attention. Most commonly studied were the stages of manufacturing and usage, with a focus on im- pact factors such as global warming potential and embodied energy. For tall buildings, embodied en- ergy values varied widely from 0.533 MJ/m² to 883.1 GJ/m², whereas for short buildings, they ranged from 0.21 to 374.4 GJ/m². In terms of Ishwor Thapa et al./ BIBECHANA 20 (2023) 326-338 330 global warming potential, tall buildings emitted be- tween 10 and 10,010 kg CO2-eq/m² annually, but certain studies highlighted how timber structures could reduce emissions by 234.8 to 1338 kg CO2- eq/m². Emissions for shorter buildings ranged from 0.07 to 35,765 kg CO2-eq/m², with timber struc- tures lowering emissions by 12.9 to 361 kg CO2- eq/m². Lifespan varied widely, from 20 to over 100 years, for different building types in life cycle as- sessment. Functional units, the measurement units used, also differed substantially, with most using "m²" (61%), while "whole building" was used in about 20% of studies, showing a lack of standardiza- tion. Ecoinvent was the most commonly referenced database (65%) for building life cycle assessment, followed by the University of Bath ICE (11%), the U.S. database (9%), and the Australian material in- ventory database (7%). Among computer software tools, SimaPro was most frequently cited (40%), fol- lowed by ATHENA Impact Estimator (7.5%) and GaBi software (4%). The study underscores that variations in building aspects (design, materials), lifespan, functional units, and scope hinder direct comparisons of research findings [11]. In recent years, major focus areas in building LCA research have been life cycle energy assess- ment, life cycle carbon emissions assessments, LCA of building refurbishments, dynamic LCA of build- ings, uncertainty analysis in LCA of buildings, inte- gration of LCA in building rating systems, integra- tion of LCA with LCC and social LCA and BIM- based life cycle assessment of buildings [12]. A re- cent study by Fatma Abdelaal and Brian H.W. Guo suggests that using Building Information Modeling (BIM) and Life Cycle Assessment (LCA) for envi- ronmentally friendly buildings is not yet fully devel- oped. There is a significant connection between the importance of BIM and LCA for these buildings. The people involved view BIM and LCA positively, seeing their potential for integration. However, the actual use of BIM and LCA does not match these positive views, indicating a need for substantial ef- forts to effectively implement and integrate them into green buildings [13]. 3.2 Highway Engineering Currently, researchers focus on the field of LCA in Highway Engineering domains, including devel- oping advanced methodologies to quantify envi- ronmental impacts, integrating LCA into decision- making processes, and exploring innovative mate- rials and technologies to enhance sustainability in infrastructure projects. Researchers aim to opti- mize design and construction strategies, minimize energy consumption, emissions, and resource deple- tion, and promote the adoption of greener trans- portation solutions to create more resilient and en- vironmentally friendly transportation systems. A study provides a comprehensive review, highlight- ing research gaps, including areas such as inventory analysis, and locally relevant data collection, ad- dressing aspects such as surface roughness, noise, lighting, and albedo, considering the temporal and consequential aspects of the pavement life cycle and conducting sensitivity analyses [14]. In another study, the use of innovative construction techniques such as 3D printing is being researched [15]. A re- cent study gathered past research on highway pave- ment studies, analyzed life cycle steps and environ- ment impact indicators and proposed a method for selecting flexible road pavement structures through stages including design, cost analysis, life cycle im- pact assessment, and integration of impact assess- ment with costs. The findings suggest that pave- ment with a bitumen-stabilized base containing re- cycled material performs best in terms of cost and environmental impact assessment, given a specific design criterion, while highlighting the influence of design parameters on pavement choices [16]. An- other study reviewed various LCA methodologies for pavement and performed a comparative life cy- cle assessment (LCA) to assess the environmen- tal impacts of using recycled concrete aggregates (RCAs) instead of natural aggregates in Hot Mix Asphalt (HMA) production. The analysis found that mixes with 15% and 30% RCA replacements were more environmentally friendly than the con- ventional mixture, but the mix with 45% RCA showed poorer environmental performance than the conventional mix [17]. This combined investigation of structure and environment illustrates the ben- efits of replacing primary natural aggregate (NA) with recycled construction and demolition waste aggregate (CDW-RA) in subbase layers for flexi- ble and semi-rigid road pavements. Various pave- ment structures featuring a 0.30 m subbase layer constructed from four materials, including two un- bound and two cement-stabilized variants using NA and CDW-RA, were compared in terms of their structural behavior. Additionally, the study evalu- ated environmental impacts through a life cycle as- sessment (LCA) [18]. Guangli made an LCA frame- work for bridge assessment[5] and also performed LCA on a soil steel composite bridge [19]. According to [20], 67 LCA studies found in the literature were assessed and categorized into four groups: flexible pavement, rigid pavement, mixed pavement, and road infrastructure. The analysis revealed that 80% of the studies were conducted in developed nations, with only 20% from developing countries. A significant portion of road pavement LCA studies (about 76%) concentrated on material and construction phases, primarily assessing global warming potential and energy demand. A smaller proportion (10-15%) considered a broader range of Ishwor Thapa et al./ BIBECHANA 20 (2023) 326-338 331 impact categories and employed commercial soft- ware such as GaBi and SimaPro for impact assess- ment. Of the 67 studies, 19 pertained to flexible pavements, 4 to rigid pavements, 30 to a combina- tion of both, and 14 to road infrastructure. No- tably, certain road infrastructure components, such as bridges, tunnels, drainage, lighting, and road marking, were analyzed, whereas others, such as culverts, toll plazas, and vehicle underpasses were excluded. Most studies relied on secondary or back- ground data for life cycle inventory. Only 18 of the 67 studies conducted sensitivity analyses and only 6 performed uncertainty analyses. This study high- lights the need to encompass all related infrastruc- tures alongside road pavements and emphasizes a greater focus on sensitivity and uncertainty analy- ses within transportation sector studies. Therefore, future LCA studies involving road infrastructures should address these negative repercussions and in- corporate social and economic impacts via Multi- Criteria Decision Making to enhance LCA as a ro- bust tool for sustainable decision-making [20]. 3.3 Geotechnical Engineering Within the domain of general geotechnical engineer- ing literature, the primary focus of most papers is developmental aspects. These articles also ex- plore approaches to sustainability in geotechnical engineering beyond the realm of LCA and life cy- cle cost analysis (LCCA). Alternatively, they might involve evaluations of ongoing research endeavors. A study examined sustainability within the realm of geotechnical engineering, emphasizing the im- portance of resilience and system recovery. They investigated various assessment techniques, includ- ing GeoSPeAR, LCA, and LCC. The authors intro- duced a composite sustainability index that amal- gamates resource efficiency, environmental impact derived from LCA, and socioeconomic repercus- sions during the design process [21]. Another study conducted a comprehensive review of assessments with an environmental focus on the life cycles of geotechnical systems. This exploration identified gaps that could drive future research. While the review’s scope was not all-encompassing, it yielded recommendations for future research needs. These suggestions addressed the limited coverage of im- pact categories in the existing literature and the absence of a standardized LCA framework. The re- view also acknowledged the impediments posed by the availability and quality of location-specific data, alongside the complexities of evaluating diverse soil profiles and design alternatives [22]. Raymond meticulously analyzed the categories of impact and environmental indicators in the Life Cycle Impact Assessment (LCIA) phase. Specific impact categories, such as energy and global warm- ing, were more frequently used than others. Im- pacts related to land use and soil received less at- tention, and the corresponding indicators for these categories were less developed than those related to energy and global warming [23]. In the category of ground improvement, Praticò employed LCCA to develop a model for the selection of stabilizers and stabilization methods for subgrade soil in low- volume road projects. Their method integrated the extra stabilization costs into the construction expenses for treated sections, consequently mini- mizing long-term maintenance costs [24]. Regard- ing the category of retaining walls and slope sup- port, Zastrow evaluated 30 cost-optimized earth- retaining walls using LCA, relying on input data from the Ecoinvent database. The quantities of concrete and steel, as well as the recycling status of steel, have implications for the resulting envi- ronmental impact [25]. Similarly, Das examined the sustainability and resilience aspects of slope stabilization. Their sustainability evaluation en- compassed LCA, socioeconomic consequences, and other factors, each of which was weighted based on their relative significance. Through multicrite- ria analysis, these weighted indicators yielded re- silience and sustainability indices for each stabi- lization technique. The technique with the lowest index was proposed for implementation. This pro- posed framework enabled the integration of multi- ple assessment methods into a single comparable index [26]. In the remaining categories, research was less extensive, and the number of published papers was lower than that other categories. In the category of "Cement related to ground improvement," Chang carried out a comparative study of costs and en- vironmental impacts between the use of biopoly- mers and traditional Portland cement for ground improvement applications [27]. Ishwor Thapa et al./ BIBECHANA 20 (2023) 326-338 332 Table 2: Waste Materials in Concrete Researched in the Past Three Years Author Journal Waste Material Used R Sharma [28] Innovative Infrastructure Solutions Waste coarse aggregate X Peng et al [29] Journal of Cleaner Pro- duction Waste coarse aggregate A Shukla et al [30] Materials Today: Pro- ceedings Waste marble dust Z He et al [31] Powder Technology Recycled concrete powder Z Duan et al [32] Construction and Build- ing Materials Waste coarse aggregate and Recycled concrete powder B Qi et al [33] Processes Recycled Epoxy D Yang et al [34] Case Studies in Construc- tion Materials Recycled concrete powder S Vaishnavi Devi et al [35] Materials Today: Pro- ceedings Waste coarse aggregate D Mostofinejad et al [36] Journal of Building Engi- neering Waste coarse aggregate, recycled fine aggregate, and waste glass Z Ma et al [37] Journal of Cleaner Pro- duction Recycled concrete powder J Xiao et al [38] Journal of Building Engi- neering Recycled concrete powder Md. Jahidul Islam [39] Construction and Build- ing Materials Waste coarse aggregate Fernando A. N. Silva et al [40] Buildings Waste coarse aggregate and recycled fine aggregate J Kim, H Jang [41] Journal of Cleaner Pro- duction Recycled concrete powder Y Guo et al [42] Construction and Build- ing Materials Recycled concrete powder A Aldemir et al [43] Journal of Building Engi- neering Waste coarse aggregate J. Jolly Abraham et al [44] Materials Today: Pro- ceedings Waste coarse aggregate I Patra et al [45] Sustainable Energy Tech- nologies and Assessments Waste coarse aggregate J Yang et al [46] Journal of Cleaner Pro- duction Wet-grinded submicron autoclaved aer- ated concrete waste K Khan et al [47] Materials Waste marble dust A Zhou et al [48] Resources, Conservation, and Recycling Engineering sediment waste H Al-Mosawe et al [49] Buildings Waste coarse aggregate Ishwor Thapa et al./ BIBECHANA 20 (2023) 326-338 333 Figure 3: LCA for building construction. Figure 4: LCA for Geo-technical Engineering Projects. 3.4 Construction Material Table 2 provides various research that has chosen waste materials, including waste coarse aggregate, waste marble dust, recycled concrete powder, re- cycled epoxy, waste glass, wet-grinded submicron autoclaved aerated concrete waste, and engineering sediment waste, among others. The diverse range of waste materials explored in these studies re- flects a growing interest in finding eco-friendly and cost-effective alternatives to traditional construc- tion materials. These research efforts contribute to the broader goal of reducing environmental im- pact and promoting sustainability in the construc- tion sector, potentially leading to innovative solu- tions and practices for the industry’s future. To gain a deeper understanding of each study’s spe- cific findings and implications, access to individual papers is necessary. Similarly, Figure 4 shows the waste materials used for concrete production over the past three years. The most used waste material was waste coarse aggregate. Over the past twenty years, research has been directed toward various aspects of the field. For instance, there has been a focus on incorporating Construction and Demolition Waste (CDW) mate- rials as aggregates into new concrete mixtures, as exemplified by references [50]. Furthermore, novel design approaches, includ- ing the utilization of building information modeling (BIM), have emerged, as indicated in the references [51]. Additionally, other studies, such as those cited in references [52] have evaluated the environmen- tal advantages of substituting virgin materials with CDW, while minimizing the impact on mechanical properties. Within the construction field, especially in CDW, LCA is commonly employed to select the optimal scenario among landfilling, recycling, and incineration, as discussed in [53]. Research in the past two decades has focused on incorporating Con- struction and Demolition Waste (CDW) materials in new concrete mixes, exploring design approaches such as building information modeling (BIM) and assessing the environmental benefits of replacing virgin materials with CDW without compromising mechanical properties. These efforts commonly em- ploy Life Cycle Assessment (LCA) to evaluate sus- tainability impacts across various phases of building and infrastructure projects, but challenges remain in integrating LCA into design considerations and encompassing all lifecycle stages, as highlighted by various literature reviews [54]. Zhuocheng conducted a comprehensive investi- gation and analysis encompassing 62 peer-reviewed articles, examining aspects such as goal and scope definition, life cycle inventory analysis, impact as- sessment, and interpretation of the use of timber in mass construction. These studies reveal a broad range of variations in terms of scope, duration, sys- tem boundaries, data sources, and indicators. The research covers multiple scales, including building materials, components, structures, entire buildings, and even urban contexts, with a primary focus on comparing the Life Cycle Assessment (LCA) of re- inforced concrete (RC) and cross-laminated timber (CLT) constructions. The articles predominantly assess indicators such as global warming poten- tial (GWP) and life cycle energy, indicating that mass timber buildings exhibit, on average, 23.00% higher embodied energy than RC alternatives, while RC buildings demonstrate 42.68% higher embodied greenhouse gas (GHG) emissions than mass timber alternatives [55]. Alireza conducted a systematic review of con- crete mixtures and examined the literature concern- ing the environmental effects related to life cycle assessment (LCA). The analysis encompassed two categories of environmental impact indicators: Mid- point and Endpoint. In the realm of midpoint indi- cators, various parameters were scrutinized, includ- ing global warming potential, water depletion, agri- Ishwor Thapa et al./ BIBECHANA 20 (2023) 326-338 334 cultural land use, fossil depletion, particulate mat- ter, acidification potential, embodied energy, water pollution, ozone layer depletion, eutrophication po- tential, human toxicity, and abiotic depletion po- tential. Within the Endpoint indicator category, discussions revolved around human health, ecosys- tem quality, and resource depletion. It was noted that among the various environmental impact indi- cators, Global Warming Potential and Acidification Potential were the most frequently employed in the context of LCA for concrete mixtures. In addition, the author compiled a concise sum- mary of the stages in LCA, taking into account fac- tors such as the country of origin, system bound- aries, functional units, effects of service life and compressive strength, sensitivity analysis, and the environmental impact method employed for con- ducting the LCA. The study revealed that the "crate to gate" approach was the most commonly utilized system boundary in the LCA of concrete mixes, with the CML method being the most fre- quently employed environmental impact assessment method [55]. 4 Limitations and Challenges of LCA in Civil Engineering In the realm of civil engineering, conducting accu- rate LCAs encounters numerous challenges. One of the foremost hurdles lies in sourcing precise and comprehensive data, given the multifaceted nature of project life cycles and the inconsistencies in data quality across sources. This is compounded by the scarcity of standardized databases and the result- ing uncertainty in assessment conclusions. More- over, the fast-paced and resource-constrained envi- ronment of civil engineering projects often clashes with the time and expertise required for thorough LCA. The industry’s deeply ingrained practices and limited awareness about the benefits of LCA can further hinder its integration, while the absence of standardized methodologies prevents cohesive com- parisons between studies. The intricacies of civil engineering projects, marked by uncertainty, cu- mulative effects, and adaptability, make quantify- ing environmental impacts and setting accurate sys- tem boundaries particularly intricate. Implement- ing Life Cycle Assessment (LCA) in civil engineer- ing projects presents a range of challenges that re- quire careful consideration. Foremost among these challenges is the acquisition of accurate and com- prehensive data for all stages of a project’s life cycle, a task that can be alleviated through im- proved data management systems and collabora- tion with industry organizations. Defining clear system boundaries, fostering interdisciplinary col- laboration, and addressing the shortage of LCA ex- pertise are essential to navigating the complexity of LCA. Standardization efforts and adherence to es- tablished guidelines can help ensure consistent and reliable results. Additionally, integrating LCA into project planning, educating stakeholders, and ad- vocating for supportive policies can help overcome resistance to change. The dynamic nature of envi- ronmental data necessitates sensitivity analysis and scenario planning, while effective communication strategies tailored to different audiences are vital for sharing LCA findings. Overall, these strategies can help civil engineering projects embrace LCA and contribute to more sustainable infrastructure development. Figure 5: Waste materials used for concrete pro- duction in the past three years. Figure 6: LCA for construction materials in Civil Engineering Projects. Ishwor Thapa et al./ BIBECHANA 20 (2023) 326-338 335 5 Research Gaps and Future Trends In the context of civil engineering, LCA is a vi- tal tool for evaluating the environmental impacts of infrastructure projects, however, certain research gaps impede its holistic integration. While LCA has primarily addressed environmental aspects, there is a need to incorporate socioeconomic considerations such as community impact and economic develop- ment. Existing LCA models are often static, lack- ing adaptability to dynamic project changes, user behaviors, and external factors. Cultural influences on project outcomes are overlooked, warranting in- vestigation into how cultural factors shape LCA outcomes. Resilience and adaptability also remain underexplored, as is the enhancement of data qual- ity and availability for LCA studies. Moreover, LCA’s focus on short-term impacts neglects long- term consequences, necessitating research to incor- porate maintenance and adaptation costs. Despite its policy potential, gaps persist in understanding how LCA insights inform policy decisions. Address- ing these gaps is poised to drive LCA in civil engi- neering toward a more comprehensive and impact- ful future. The future of Life Cycle Assessment (LCA) in civil engineering is expected to involve a holistic approach integrating environmental, so- cial, and economic aspects. This includes evalu- ating social impacts and long-term economic via- bility, aided by advanced data analytics, real-time monitoring through digital twin technology, and the application of circular economy principles for waste reduction and material reuse. Collaborative stakeholder engagement, machine learning, and AI are expected to enhance LCA accuracy, while LCA findings could play a more significant role in shap- ing policies and regulations. Integrating LCA with life cycle cost analysis will provide a comprehensive view of design trade-offs, aligning financial and sus- tainability objectives for more informed decision- making. Overall, LCA’s evolution in civil engineer- ing will be characterized by comprehensive assess- ments aligned with broader sustainability goals. References [1] J. B. Guinée, R. Heijungs, G. Huppes, A. Za- magni, P. Masoni, R. Buonamici, T. Ekvall, and T. Rydberg. Life cycle assessment: Past, present, and future. Environmental Science & Technology, 45(1):90–96, 2011. https://doi. org/10.1021/es101316v [2] United Nations. The sustainable development agenda, 2015. [3] Bs-en 15804:2012+a1:2013/fpra2:2019 envi- ronmental product declarations - core rules for the product category of construction products, 2019. 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