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Intelligent traffic control at nonsignalized intersections under a connected and automated vehicle (CAV) environment can reduce traffic congestion, vehicle emissions [e.g., carbon dioxide ðCO2Þ, carbon monoxide (CO), nitrogen oxide (NO)], but it is still not safe enough for an unpredictable emergency. For example, an accidental stop or slow down of a vehicle in the conflict area will cause secondary accidents of vehicles from other directions because they do not have enough distance to brake. Such risks have not been given sufficient attention in the literature. This paper proposed a safety guarantee mechanism of intersection control to avoid secondary accidents by adding a safe buffer area outside the conflict area of the intersection. To improve the traffic efficiency of intersections and reduce vehicle emissions under the mechanism, we proposed a heuristic vehicle trajectory planning control strategy based on vehicle kinematics. Three planning principles are applied to generate the microscopic trajectory for each vehicle: (1) the vehicle first decelerates and then accelerates before passing the intersection; (2) try not to change the running state of the vehicle; and (3) the vehicles do not collide with each other. Finally, to further improve efficiency, we proposed the concept of a dynamic safety area, which reduces the delay by self-adjusting the safety area to each vehicle’s trajectory. The paper selected three simulation scenarios of road intersections to validate our methodology. The simulation results show that the proposed control method with the safe buffer significantly reduces average vehicle delay and emissions compared to traditional signal control systems. Compared with the fixed buffer, in the dynamic safe buffer scenario, the average vehicle delay can be reduced by 66.94%, the throughput is increased by 18.75%, and CO2 emissions are reduced by 9.9%. The dynamic safe buffer can not only relax the safety concern of a nonsignalized intersection, which is not well addressed in the literature, but also has much better performance than the traditional intersection. [ABSTRACT FROM AUTHOR]

A vertical extension (VE) involves the construction of additional floor space on top of an existing base building. With growing urban populations and an urgency to reduce building-related carbon emissions, VEs might have the potential to be a sustainable and innovative solution to overcome the shortage of urban spaces. However, despite the growing number of projects and the emerging academic literature, limited research has documented the decisions that inform the development of VE projects or the lessons learned from stakeholders that were involved in their creation. This paper presents the early decision-making processes that are undertaken to select a VE as an appropriate development type to construct in practice, and the common challenges and solutions during its realization, through semistructured interviews with a broad range of stakeholders, including developers, contractors, architects, and structural engineers that have been involved in recently completed VE projects. The results identify that the main driver of VEs is economic profit, followed by sustainability goals and the desire to stay on the same site. The challenges are related to the complex design and coordination of VE projects, and onsite construction challenges. In addition, this paper identifies the diverse structural support and reinforcement strategies that are used in VEs and contributes to the knowledge by capturing the different aesthetic and construction approaches that are used in practice. [ABSTRACT FROM AUTHOR]

Despite the recognition of the built environment as a sector with high potential for reducing embodied emissions, there is a lack of national-level data on embodied carbon emissions attributed to the US commercial building stocks. Hence, there is a need to benchmark the current state of embodied emissions attributed to the commercial built environment and the impact of circular economy (CE) policies for their decarbonization to facilitate well-informed decision-making. This paper fills this knowledge gap through providing policy makers with a framework that estimates the current and future projections of embodied carbon emissions attributable to the US commercial building stocks and highlighting the decarbonization potential of multiple CE policies. To this end, the following multistep research methodology was adopted: (1) collecting and integrating relevant data; (2) conceptualizing and initializing a system dynamics (SD) model; (3) developing subsystems and coflow structures within the SD model using aggregated stock data from the National Energy Modeling System; (4) verifying and testing the developed SD model; and finally (5) suggesting policies and conducting scenario analysis using CE policy precedents. Findings reveal that in the baseline scenario, cumulative emissions are projected to reach 5,605 MtCO2e by 2050. As for the scenario analysis, the unit size reduction policy emerged as the most impactful single policy, achieving a remarkable 38.8% decarbonization. Whereas the comprehensive CE policy that optimizes floorspace demand and the carbon intensity of materials, exhibited a 52% decarbonization potential by midcentury. As such, this study contributes to the body of knowledge by benchmarking emissions projections, providing insights regarding CE decarbonization strategies, their associated primary stakeholders and implementation pathways. Ultimately, by embracing a holistic approach toward CE policies and harnessing accurate and standardized data on building embodied emissions, stakeholders can effectively attain decarbonization goals and promote a sustainable built environment. [ABSTRACT FROM AUTHOR]

Reasonable earthmoving-equipment combinations have helped to reduce duration and cost in the construction industry traditionally. However, reducing carbon emissions in earthmoving operations is highly desirable because earthmoving operations involve a large number of heavy equipment, which produce high carbon emissions. It is necessary to study a novel equipment combination optimization model considering decreasing carbon emissions in addition to duration and cost. Hence, a triobjective equipment combination optimization (ECO) model is developed, minimizing carbon emissions as well as project duration and cost. In this model, the excavation and transportation processes of earthwork are regarded as a queuing system, and queuing theory is integrated directly into the model to compute the involved parameters instead of a simulation. On the other hand, for obtaining the optimal solution set of the multiobjective problems with more objectives, a novel two-archive multiobjective particle swarm algorithm is proposed, which updates individuals in archives by not only Pareto domination but also an indicator that can assess solution quality. A real case study demonstrated that the model can efficiently provide a reasonable earthmoving-equipment combination considering the trade-off among carbon emissions, duration, and cost for managers. A multiobjective model for obtaining the optimal earthmoving-equipment combination is proposed in this paper. In addition to traditional reductions in duration and cost, the model also considers sustainability requirements by reducing carbon emissions in the construction industry. In other words, this model can offer the solutions of equipment combinations in terms of not only reducing the cost and duration to construction managers, but also reducing carbon emissions. Instead of one combination of earthmoving equipment, a set of nondominated solutions is offered in this model, and this allows managers to make choices based on specific site conditions. In addition, the authors have improved the traditional algorithm to obtain the solutions to better meet the needs of users. This new earthmoving-equipment combination optimization model can quickly get reasonable equipment combinations and helps minimize carbon emissions as well as duration and cost. This model has been applied to a real earthwork project in China and gave the optimal excavator-truck configuration that satisfied the contractor. [ABSTRACT FROM AUTHOR]

Reducing carbon emissions in the construction sector is essential in a period of climate emergency. Disassembly and reuse of structural members are considered to reduce the carbon emissions from the construction and deconstruction of buildings. In this context, it is important to review the current state of the art to provide a framework for the development of future structural systems that can enable the easy disassembly and reuse of steel-framed buildings. This paper (1) presents a review of more than 100 documents to discuss the feasibility of disassembly and reuse of structural members; (2) develops detailed schematic illustrations to explain the design concepts and the underlying mechanics governing the behavior of demountable connections; (3) sheds lights on the technical and design challenges to implement disassembly and reuse of the structural members; and (4) defines future research needs to facilitate the disassembly and reuse of the structural members. [ABSTRACT FROM AUTHOR]

Red beds (RBs) are widely distributed in all continents of the world. With the rapid development of road and railway construction, the construction of roads and railways in RB areas is increasing. However, when RB is the filler, it will expose three aspects of serious deficiencies in compaction, mechanical bearing capacity, and water stability, which will cause fatal harm to the subgrade. Therefore, RB has to be abandoned and cannot be used as a subgrade filler. In this paper, different microwave irradiation temperatures (DMITs) from room temperature of 25°C to 700°C were used to reveal the enhancing mechanism of RB in three aspects based on the analysis results of microscopic composition and structure. The microscopic composition and structure show that RB can be divided into a low-temperature section (25°C–400°C) and a high-temperature section (500°C–700°C) under the microwave condition. The low-temperature section has some improvement in the engineering performance of RB, but the influence is limited. The engineering performance of RB is improved completely in the high-temperature section. Specifically, the coarse size of RB increases with the rise in microwave temperature, which is beneficial for improving fine size. The compaction property of RB is not largely affected by the water content and can still meet the most stringent subgrade filler requirements, even under saturated conditions or 0. The California bearing ratio (CBR) value can maintain more than 20% under the ultimate working condition, far higher than the code requirements. The increase of internal friction angle and cohesion can enhance the stability of the cut slope, which is conducive to construction in remote mountainous areas. The water resistance of RB is positively correlated with the microwave irradiation temperature, especially at 700°C; RB experiences secondary hardening after encountering water, the mechanical strength increases, and the softening coefficient reaches 107.44%. The research shows that after microwave high-temperature stabilization, the engineering characteristics of the RB are thoroughly strengthened, and it becomes a high-quality subgrade filler to eliminate the three diseases of RB subgrade completely. Compared with the traditional method of adding stabilizers, microwave in situ RB stabilization reduces the site construction's complexity, saves a lot of stabilizer use and transportation costs, and can effectively reduce carbon emissions. This study provides a positive perspective on the in situ application of the RB soft rock subgrade. It could be a starting point for understanding the microwave-based stabilization of soft rock soils subgrade filler in situ. [ABSTRACT FROM AUTHOR]

The increasing awareness of sustainability has resulted in the progressive regulation of contractors for public projects to lower the pollution associated with their equipment fleet. Nevertheless, such implementation has not been fully developed yet due to the challenges this presents to contractor profitability and the practical usefulness of decision-support tools. This paper developed a sustainable equipment fleet (SEF) decision-support optimization model with the capability to reduce the CO2 emissions of construction equipment and to minimize the equipment fleet modification cost, subject to the contractor's budget and time constraints. The model utilizes a multiobjective genetic algorithm (GA) to search for the combination of equipment utilization, equipment model, and sustainable options that provide the optimal equipment fleet options to contractors. The results from the case study of a road construction project demonstrated the tradeoff between emissions and costs, with a wide range of optimal sustainable equipment fleet options. In addition, the fuel equivalent ratio (FER) and the equipment cost-effective ratio (CER) were newly established to normalize pollutant generation and equipment investment and to enable equipment comparisons for facilitating equipment selection by the contractor. The findings suggested that equipment selection involving a lower FER is preferable for sustainability and likewise, a lower CER for the cost aspect. However, effectiveness was measured as the proportion of FER to CER, with higher effectiveness when the proportion was lower. This paper facilitates the assessment and prioritization by construction companies of their equipment investment options to satisfy sustainability requirements. [ABSTRACT FROM AUTHOR]

In this paper, the ability of resource treatment of black smelly river sediment to reduce life-cycle greenhouse gas (GHG) emissions and its environmental benefits were calculated using the US EPA life-cycle assessment (LCA) model. Different from previous studies, this paper used the willingness-to-pay method to determine the weight factors of various environmental impact types in this study and proposed a calculation model of carbon emissions and environmental benefits in the whole process of resource utilization of sediment, rather than a new method to treat black smelly river sediment. Take the Qingxi River sediment treatment and recycling project in Dongguan, China, as an example: the carbon reduction, environmental impact, and environmental benefit of different stages of sediment treatment are calculated. The results show that 93.419 kg of carbon dioxide, 0.202 kg of methane, and 0.001 kg of nitrous oxide are produced for 1 t of river sediment, in which the preparation process of unburned brick contributes 99% of carbon dioxide, 82.67% of methane, and 100% of nitrous oxide emissions and is the stage that produces the most greenhouse gases. The 1 t of sediment resource treatment can reduce the generation of 29.066 kg carbon dioxide and 0.855 kg of methane. The comprehensive net environmental benefit of processing 1 t of river sediment is 1.492 yuan, and the environmental benefit is 1.684 times the environmental cost. This study identified that the treatment and recycling of river sediment has better environmental benefits. The preparation process of unburned brick can be optimized to further reduce carbon emissions and produce better environmental benefits. [ABSTRACT FROM AUTHOR]

As a clean fuel with low carbon emissions, hydrogen-rich syngas has higher flame propagation speed and higher adiabatic flame temperature than other gaseous fuels, so its local flame propagation characteristics are also different from other fuels. In this paper, an experimental study on the hydrogen-rich syngas turbulent premixed flame was carried out at different pressures [101–303 kPa (1.0–3.0 bar)] when the hydrogen fraction was 65%, the fan speed was 3,559 revolutions/min (rpm), and the equivalence ratio was 1.0. The results show that with the propagation of the flame or the increase in pressure, the fluctuation amplitude of flame local radius and flame local pulsation radius becomes smaller. Similarly, the flame local propagation speed increases with the increase of pressure. By analyzing the correlation between the turbulent premixed flame front structure and the turbulent premixed flame propagation process in hydrogen-rich syngas, it is found that when the pressure increases, the correlation between the flame local pulsation propagation speed and the flame local pulsation radius weakens. [ABSTRACT FROM AUTHOR]

The Chinese government continues to contribute to tackling the global climate challenge and plans to continue lowering carbon emissions in the transportation infrastructure field. The comprehensive assessment of the impact of carbon emissions is mainly focused on high-speed railways (HSRs). This paper proposes a life-cycle cost considering carbon emissions (LCCCCE) model for HSR projects, which consists of a general life-cycle cost (GLCC) model and a quantified carbon emissions cost (CEC) model. The Beijing-Shanghai HSR is employed as a case study, in which the LCCCCE and sensitivity of carbon emission factors are analyzed using the proposed methodology. The results show that the LCCCCE of the Beijing-Shanghai HSR is 64.56 billion USD, and that its CEC is 1.04 billion USD, which contributes 1.61% to the LCCCCE. Thus, the LCCCCE analysis of HSRs or transportation infrastructure projects is an effective methodology to quantify the impacts of carbon emissions in China and around the world. [ABSTRACT FROM AUTHOR]

Railways are an efficient transport mode, but building and maintaining railway tracks has a significant environmental impact in terms of CO2 emissions and use of raw materials. This is particularly true for slab tracks, which require large quantities of concrete. They are also more expensive to build than conventional ballasted tracks, but require less maintenance and have other advantages that make them a good alternative, especially for high-speed lines. To contribute to more sustainable railways, this paper aims to optimize the design of one of the most common slab track typologies: RHEDA 2000. The main objective is to reduce the amount of concrete required to build the slab without compromising its performance and durability. To do so, a model based on finite-element method (FEM) of the track was used, paired with a kriging metamodel to allow analyzing multiple options of slab thickness and concrete strength in a timely manner. By means of kriging, optimal solutions were obtained and then validated through the FEM model to ensure that predefined mechanical and geometrical constraints were met. Starting from an initial setup with a 30-cm slab made of concrete with a characteristic strength of 40 MPa, an optimized solution was reached, consisting of a 24-cm slab made of concrete with a strength of 45 MPa, which yields a cost reduction of 17.5%. This process may be now applied to other slab typologies to obtain more sustainable designs. [ABSTRACT FROM AUTHOR]

Off-site construction (OSC) methods have captured significant recognition during the last decade due to a range of benefits offered, from reduced construction time and cost to improved efficiency and environmental savings. OSC is proven to have enhanced performance in environmental issues such as waste generation and carbon emissions. However, even with well-documented benefits, by 2018, no major market has yet exceeded 20% of OSC penetration. Thus, identifying factors that advanced and enhanced the environmental performance of OSC from current research to understand the learnings and strategies is timely. A systematic literature review on the role of developed and developing economies in the environmental sustainability of off-site constructed buildings and identifying critical success factors (CSFs) is a novel research opportunity in the current literature. Thus, this research presents a systematic review of the environmental sustainability of OSC (ESOSC) with a clear focus on comparing OSC and its advancements in developed and developing countries. The research methodology involves a bibliometric analysis (BA) followed by an in-depth qualitative discussion. The BA identified key research trends, gaps, and governing countries in ESOSC research. The critical review has significantly focused on comparing the ESOSC studies in developed and developing countries to understand the differences, similarities, CSFs, and future opportunities. The outcomes of BA and critical discussion suggested that further research is required in the following topic areas: comprehensive sustainability assessments, smart/computerized technology integration, prefabrication rate-related research, integration of circular economy/sustainable development goals, and developing region-specific research. The theoretical value of the paper is in facilitating a solid basis for future investigations into the role of these economies in the triple bottom line of sustainability. The practical contribution of the study is to guide OSC stakeholders to increase the rate of OSC adoption and boost environmental performance. [ABSTRACT FROM AUTHOR]

Drinking water and natural gas are essential goods provided by municipal distribution networks. In order for there to be a reliable provision of such commodities, infrastructure managers must regularly dispatch vehicles to perform tasks such as valve and hydrant inspections and meter replacements. As public concerns about sustainability grow, managers must look for ways to reduce carbon emissions. This, however, should be done without jeopardizing service. One conceivable approach is to train staff to perform additional maintenance tasks so that combined work packages can be carried out. This would require resources to be spent in different areas, such as supplemental worker training and organizational restructuring of the utility. Infrastructure managers must thus weigh the expected efficiency gains against the associated costs. The infrastructure asset management process combined with digitalization are powerful tools to assess such questions. Unfortunately, digitalization in the infrastructure sector lags behind other sectors of the economy. To bridge this gap, real-world examples are needed to further spur adoption. This paper addresses this need with a methodology and case study for infrastructure managers of water and gas networks. Specifically, this paper presents a methodology to quantify the resource requirements of operational maintenance programs for a large municipality. As utilities plan maintenance routes differently, four algorithms are used to model the resource requirements of the status quo. The effect of prioritization as well as frequency of inspections/replacements is considered. [ABSTRACT FROM AUTHOR]

Most geopolymer research claims a substantial reduction in carbon dioxide emissions compared with ordinary portland cement concrete. However, geopolymer concretes are not all equally eco-friendly. The environmental benefits of geopolymer concrete cannot be taken for granted. Modeling emissions is necessary to assess the environmental impact of each geopolymer mix. Unfortunately, only studies concerned with carbon dioxide emissions care to provide sophisticated emissions modeling. Such modeling is practically nonexistent for other geopolymer studies; because function-oriented geopolymer research tends to assume the environmental eminence of their designed mixes. This research reviews the last 7 years of geopolymer concrete research to assess the sustainability of the mixes designed by researchers worldwide and to highlight any bad environmental practices in the mix design. The nominal CO2-e equivalent emissions for geopolymer concrete mixes varied from 56 to 661 kg-CO2/m3 for the surveyed mixes. SOx and NOx emissions reached 1,865 g-SOx/m3 and 1,161 g-NOx/m3 , respectively. Finally, this paper recommends a simple method for estimating a nominal carbon dioxide emissions value, which can be easily implemented in future geopolymer research. [ABSTRACT FROM AUTHOR]

This paper represents a series of laboratory tests to illustrate the effects of natural zeolite and sulfate environment on the mechanical behavior, hydraulic properties, and microstructure of plastic concrete. Plastic concrete (Pl-C) is comprised of cement, water, aggregate, and bentonite. Because cement production is responsible for a significant amount of carbon dioxide emissions into the atmosphere, cement was replaced in five different percentages of 0%, 10%, 15%, 20%, and 25% by natural zeolite (Z). Moreover, all the specimens were cured in chambers simulating sulfate attack. The mechanical behavior of plastic concrete containing natural zeolite (Pl-CZ) was studied using a series of confined and unconfined compression tests. Hydraulic properties were evaluated using three different confining pressures of 200, 350, and 500 kPa. Scanning electron microscopy (SEM) images were utilized to explore the microstructure of Pl-CZ specimens. The test results show that, although increasing the zeolite content decreased the unconfined strength, peak strength, and the elastic modulus in the early ages, at the later ages, it increased the unconfined strength as well as the peak strength and the elastic modulus, while it decreased the permeability. As illustrated in SEM images, specimens cured in the sulfate environment indicated lower porosity which led to having higher unconfined strength, elastic modulus, and peak strength, along with lower permeability. [ABSTRACT FROM AUTHOR]

Water distribution networks (WDNs) confront momentous challenges, including the need to meet continuously increased demand, combat unforeseen disruptions, and reduce carbon emissions. Developing efficient plans for resilience enhancement of WDNs thus is essential recognizing the ubiquitous nature of WDNs and increased frequency and destructive severity of hazardous events. This paper presents a resilience-driven multiobjective optimization model to maximize the resilience of WDNs while minimizing the life-cycle cost and carbon emissions. Enhancement actions first are determined and clustered into work packages, and then an optimized schedule is generated considering various operational and managerial factors. A real WDN in the city of London, Ontario, was utilized to demonstrate the proposed model's practicality. The resilience increased by 24% with CAD 1.6 million investment. Additionally, cost saving of about 33% is achievable if the proposed model is employed instead of a currently utilized practice. The developed model is expected to help city managers establish optimal resilience enhancement plans, considering tight available budgets and limited workforce. [ABSTRACT FROM AUTHOR]

Carbon emission reduction (CER) in the construction industry can aid in achieving the international community's carbon neutrality target. However, the low motivation of construction enterprises to reduce carbon emissions and the unsatisfactory effect of CER are still unresolved issues. This study aims to address these issues by constructing a building supply chain (BSC) consisting of a developer and a contractor using government subsidies and cost-sharing contracts. The optimal government subsidy and feedback equilibrium strategies of the BSC are examined using a combination of differential game theory and numerical simulations. The findings demonstrate that (1) cost-sharing contracts may enhance developer and contractor profits and building CER, goodwill, and demand without relying on government subsidies; (2) when subsidized by the government, each equilibrium strategy meets or exceeds the performance of the centralized model, with the cost-sharing contract having a negligible effect on the enhancement of each equilibrium strategy; and (3) both the game structure and the positioning of construction enterprises in the BSC are connected to the number of government subsidies. The city of Shenzhen, one of China's first low-carbon pilot cities, provides a realistic environment for the simulation analysis, with the Block K residential building in Nanshan District serving as a case study. Furthermore, this work contributes to the body of knowledge by proposing a novel CER model for the BSC using differential game theory. The research provides new insights into the role of government subsidies in shaping profit distribution, game structure, and enterprise positioning. Findings demonstrate the value of cost-sharing contracts in improving CER, goodwill, demand, and profits when implemented collaboratively. This advances the theoretical understanding of incentives and strategies for promoting CER in construction. This research highlights the importance of collaborative efforts between the government and the building supply chain (BSC) to promote sustainable construction and carbon emission reduction (CER). The study found that government subsidies can be an effective tool to encourage developers and contractors to adopt CER practices. However, relying solely on subsidies is insufficient—collaboration through mechanisms such as cost-sharing contracts can further enhance sustainability outcomes when enterprises work together. To facilitate low-carbon construction, the government could provide subsidies for developers' promotional and marketing activities as well as funding for contractors' research and development of sustainable materials and technologies. Financial incentives such as tax breaks and preferential lending for potential homebuyers can also accelerate consumer demand. Ultimately, creating a supportive environment where enterprises proactively pursue CER creates a win–win situation where the BSC becomes more sustainable while firms improve their branding and profitability. The insights from this research highlight the need for a multipronged approach. Governments play a key role through policy and financial support. Realizing the full potential of sustainable construction also requires active participation from developers, contractors, and consumers. By outlining optimal strategies and incentives, this study provides valuable guidance to construction industry stakeholders seeking to implement CER collaboratively. [ABSTRACT FROM AUTHOR]

Cement has historically been a major contributor to carbon dioxide emissions, and substituting cement in concrete with alternative cementitious materials will lead to a decrease in carbon footprints. A vast amount of literature focuses on the mechanical properties and performance of concrete partially replaced with different cementitious materials. However, the literature on the structural performance of concrete with different cementitious materials is very limited. Therefore, the main aim of the current experimental study is to evaluate the flexural and shear performance of reinforced concrete (RC) beams cast with various replacement percentages of ordinary Portland cement (OPC) with supplementary cementitious materials (SCM) such as ground granulated blast furnace slag (GGBS) and fly ash. A total of 33 RC beams were cast with 50% and 70% replacement of cement with GGBS and fly ash. In addition, the tensile and compressive strengths of the different mixes with GGBS and fly ash were also compared with the 100% OPC mix at 28 and 56 days. All beams were subjected to monotonic four-point bending tests and load-deflection response curves along with failure modes were presented. The experimental results showed that the average compressive and tensile strength of mixes with GGBS and fly ash replacement were comparable with OPC. The mixes with 50% replacement and higher usage of GGBS showed higher compressive strengths compared to mixes with 70% replacement. In addition, the flexural performance of beams with GGBS and fly ash were comparable to the specimen with 100% OPC. Even GGBS and fly ash replacement increased the stiffness and yield strength of the beam specimens by 36 and 16% compared to the control specimen. The specimens tested at 56 days with higher usage of fly ash and 50% replacement showed the highest flexural load as compared with other specimens. In the case of the shear specimens, the normalized ultimate shear capacity of RC beams is not significantly affected when OPC is replaced with 50% and 70% of GGBS and fly ash, respectively. Therefore, it can be concluded that the overall behavior of SCM beams was comparable to that of the control OPC beams. The ACI 318-19 design guidelines were also used to predict the flexural and shear capacity of RC beams cast with GGBS and fly ash. The aforementioned experiments indicate the viability and effectiveness of cement replacements in concrete with SCM, which in return, contribute to lower carbon footprints. [ABSTRACT FROM AUTHOR]

Given the urgent need for decarbonization of the construction industry due to its pivotal role in global greenhouse gas emissions, industrialized construction (IC) has emerged as a promising technique to change the productivity, quality, and sustainability of construction. Although some evidence and case studies reveal that IC has distinct decarbonization advantages compared with traditional construction, there still is a need to analyze best practices, opportunities, and challenges in order to guide industry practitioners and to define key knowledge gaps. A systematic review was conducted following the three core steps: database search; research gap identification, analysis according to key lifecycle stages, and decarbonization themes. This synthesized existing academic works at the intersection of industrialized construction and decarbonization to provide a comprehensive understanding of decarbonization in IC. The findings show that although a significant amount of research focused on emissions during project stages A1–A3, there is a noticeable research gap in evaluating the carbon emissions associated with transportation, operations, and end-of-life attributes of IC. Moreover, the absence of real-time assessments during the B6–B7 operational stages impedes optimal carbon emission assessment. The verbosity of carbon estimation and tracking methodologies also adds challenges to ensuring that additional carbon impacts of IC are adequately offset by improved efficiency and lower onsite emissions. The potential of decarbonization of IC can be explored further by future research on the standardization of life-cycle assessments, development of continuous carbon-tracking methodologies, and application of alternative materials and new technologies. Practical Applications: The effectiveness of IC practices in reducing carbon emissions may vary, as deduced from the reviewed literature. However, the conscientious selection of materials characterized by low embodied emissions can contribute to a reduction in carbon emissions, applicable to both IC and non-IC projects. IC projects are uniquely positioned to achieve an even greater reduction in carbon emissions because of a unique process that innately offers waste reduction and product quality improvements. Although a considerable volume of research has focused on estimating carbon emissions, there appears to be a gap in tracking the precise quantity of emissions across various life-cycle phases within IC. Although there is considerable research on decarbonization in prefabricated components, research on specific life-cycle phases still is lagging. Furthermore, future research should prioritize investigating similar opportunities for three-dimensional (3D) volumetric systems. [ABSTRACT FROM AUTHOR]

Air pollution and carbon emissions are highly homogeneous and closely correlated. The cobenefit and spillover effects of environmental policies have garnered increasing attention in recent years. This study adopts low-carbon city pilot policies as a policy perspective to investigate the comprehensive effect of reducing air pollution and mitigating carbon emissions. By employing the difference-in-differences model, this study examines the impact of low-carbon city pilot policies on air pollution and carbon emissions across 281 Chinese cities, further analyzing the influencing mechanism and heterogeneity of policy effects. The findings of this study indicated that: (1) low-carbon city pilot policies could significantly mitigate urban carbon emissions (−0.117), while increasing air pollution (0.134), thus resulting in the spillover effect. The benchmark regression results passed a series of robustness tests. (2) The spillover effect generated through three influencing mechanisms: market resource crowd-out, industrial structure lock-in, and environmental policy substitution. (3) The local characteristics of cities, such as economic development, resource endowment, and administrative authority, would inevitably influence the implementation of low-carbon city pilot policies. Eastern cities, resource-based cities, and prefecture-level cities have yielded obvious spillover effects. Consequently, this study proposes several policy implications to coordinate urban planning to curb air pollution and carbon emissions, including exploring policy combinations, guiding resource inputs, considering local characteristics, and establishing comprehensive monitoring systems. [ABSTRACT FROM AUTHOR]

As an essential sector of the construction industry, bridge construction produces a large amount of carbon dioxide and other greenhouse gases, greatly intensifying the global greenhouse effect. Prefabricated reinforced concrete (RC) T-beams are a vital type of structural element widely used in bridge construction projects such as river-spanning bridges, high-speed railways, and urban expressways. This study proposes a bridge structural optimization framework using building information modeling (BIM) and two-stage metaheuristic searching (MS) in order to minimize the carbon emission of prefabricated RC T-beams. Under the constraints of corresponding design specifications, the first stage of the proposed MS is utilized to optimize the longitudinal steel section size and area of the T-beam, with carbon emission as the optimization objective. The optimal combination of rebar diameters is then obtained in the second stage of the proposed MS. An illustrative example is also provided to demonstrate the performance of the proposed framework. Moreover, the proposed framework is compared with conventional approaches as well as other metaheuristic algorithms to validate the developed optimization approach. [ABSTRACT FROM AUTHOR]

Massive infrastructure constructions have resulted in scarcity of river sand resources. Previous studies and applications proved dune sand can partially replace river sand used in engineering to alleviate the supply and demand contradiction of river sand. However, due to the dune sand is finer, rounder and smoother than river sand, determining the appropriate proportion of dune sand for designing engineered dune sand concrete (DSC) remains challenging. To tackle this challenge, a mix design method for DSC was proposed via close packing model and mortar film thickness theory. Specifically, the close packing model was used to confirm dune sand content and sand ratio, then the dune sand and river sand were mixed to obtain engineering-standard mixed sand. The mortar film thickness theory was utilized to determine the mortar volume and to tailor the concrete slump. By proper design, the DSC achieved the 28-d compressive strengths of 50 MPa along with good workability. Increasing the thickness of the mortar film from 0.3 to 0.9 mm leads to significant changes in DSC performance. For per 0.1 mm increase in thickness, there is an average change of 14.25 mm in slump, 11.35 kg/m3 in dry density, 0.90 MPa in compressive strength at 28 d, 15.06 kg/m3 in CO2 emission, 85.3 MJ/m3 in energy consumption, and 1.2 USD/m3 in cost. The designed DSC achieved a relatively low cement intensity (CI) value of 6.23 kg/m3/MPa , implying that DSC exhibits good eco-efficiency. Therefore, the proposed hybrid design approach can guide the design of engineered DSCs with excellent mechanical properties as well as environmental and economic performance. [ABSTRACT FROM AUTHOR]

Grain security is the foundation for national stability and prosperity. In China, grain production depends heavily on irrigation water, direct energy for machinery use, and indirect energy (such as fertilizers, pesticides, and agricultural film), resulting in growing pressure on water supply and demand and high carbon emissions. Therefore, it is urgent to study the regulation of planting structures to reduce the irrigation water input and carbon emissions on the premise of grain security. It is within the scope of the water–energy–food nexus. In China, water resources are mostly managed at the basin scale. Because of missing or inadequate basin-scale data, in this study, the Yellow River Basin (YRB) was chosen as an example to shed light on basin scale regulation analysis; YRB is an important grain production base in China, but it is facing serious water shortage and severe environmental problems. First, production and consumption of diverse grain species in the basin were estimated using remote sensing and statistical data simultaneously. Then, the blue water and carbon footprints were calculated to analyze the water use and carbon emission characteristics of grain production. Finally, the grain planting structure was regulated to reduce the irrigation water input and carbon emissions. Our findings suggest that, with effective planting structure regulation, 4.11×108 m3 irrigation water and 16.98×104 tons CO2 equivalents could be reduced and the grain production increased by about 31×104 tons in the YRB. This study can be viewed as a step towards the use of multisource data to facilitate the analysis of diverse grain species characteristics and sustainable grain development while considering the water–energy–food nexus. A combination of effective planting structure regulation in arid regions and policies will contribute to an increase in grain production as well as saving of resources. [ABSTRACT FROM AUTHOR]

Bridges play a significant role in urban areas, and their performance and safety are highly related to the carbon emissions of infrastructure systems. Previous studies have mainly offered maintenance policies that balance structural safety with overall costs. Considering the goal of achieving near-zero global carbon emissions by 2050, this study proposes a policymaking agent based on a convolutional autoencoder–structured deep-Q network (ConvAE-DQN) for managing deteriorating bridges at the network level while considering sustainability performance. This agent considers environmental, economic, and safety metrics, including spatially correlated structural failure probability, traffic volume, bridge size, and others, which are transformed into a multiattribute utility model to form the reward function. Reinforcement learning is employed to optimize the life-cycle maintenance planning to minimize the total carbon emissions and economic costs while maximizing regional safety performance. The proposed method is substantiated by developing sustainable life-cycle maintenance policies for an existing bridge network in Northern China. It is found that the proposed ConvAE-DQN policymaking agent could output efficient and sustainable life-cycle maintenance policies, which are annually stable and easy to schedule. The utility-based reward function enhances the stability and convergence efficiency of the algorithm. This study also assesses the impact of budget levels on network-level bridge safety and carbon footprint. [ABSTRACT FROM AUTHOR]

The lighting system as a crucial urban infrastructure needs to be maintained to uphold good performance. The planning and scheduling of maintenance for geographically distributed lighting systems is a complex research problem as well as a challenge in practice due to resource constraints and the complexity of route planning. This study proposes a multiple-objective decision-support model (MODSM) for lighting maintenance routing, which considers both the carbon emissions generated during the maintenance process and the loss of efficiency due to workload imbalance among maintenance crews. In the proposed model, carbon emissions are converted into a carbon tax index as part of the total cost index (along with the pure cost index), while the workload balance is measured by the standard deviation of workload indexes among the crews. To address the identified problem, an improved genetic algorithm is used to identify the optimal solution for group relamping. A numerical example is provided to demonstrate the suitability of the developed model to the selection of an optimal maintenance scheme, including the number of maintenance crews and their corresponding maintenance routes. Finally, the performance of the proposed model is assessed by sensitivity analysis and comparison with the traditional method. Integrating the interests of multiple stakeholders and environmental protection, the MODSM for lighting maintenance routing developed in this study can provide a helpful tool for researchers and practitioners in the construction engineering and management community to formulate a more comprehensive decision into maintenance management. [ABSTRACT FROM AUTHOR]

In the context of global efforts to pursue carbon neutrality, the methanol-diesel reactivity controlled compression ignition (RCCI) combustion has become a promising strategy for diesel engines to reduce emissions with higher thermal efficiency. To further improve the fuel economy of the methanol–diesel RCCI engine and reduce its unregulated emissions, the effects of methanol substitution rate (MSR) and exhaust gas recirculation (EGR) on fuel economy, CO2 , MeOH, and H-CHO emissions at different engine speed and load conditions were tested. The conversion efficiency of a conventional diesel oxidation catalyst (DOC) in oxidizing the unregulated emissions under the World Harmonized Steady-State Cycle (WHSC) was also evaluated. The results showed that running the engine in methanol-diesel RCCI mode can significantly improve fuel economy at medium to high loads [greater than 1.18 MPa brake mean effective pressure (BMEP)]. The equivalent brake specific fuel consumption (ESFC) in the RCCI mode was lower than that of the baseline CDC mode, and the utilization of EGR can further improved fuel economy at lower load conditions. The MeOH and H-CHO emissions increased as the MSR increased, and they decreased as the load level and EGR rate increased. The CO2 emissions decreased as the MSR increased, but they increased as the EGR rate increased. The conversion efficiencies of DOC for MeOH, H-CHO and aromatic hydrocarbons (AHC) were around 93%, 84%, and 61%, respectively, under the WHSC test. Exhaust after-treatment by DOC is an effective solution to reduce unburned MeOH and H-CHO from methanol-diesel dual-fuel engines, and to extend RCCI operating range. [ABSTRACT FROM AUTHOR]

Urban transportation is viewed as the second leading source of carbon dioxide emissions. The growing number of vehicles and road infrastructure-based supply in Indian cities is viewed as the essential driver of climate change and relevant consequences affecting the sustainability of cities. In this study, sustainable transport measures were analyzed to understand the emission mitigation potential of the Bengaluru Metropolitan Region's transport sector in Karnataka, India. Relevant policies were identified under the planning, regulatory, economic, and technological instruments and grouped under four policy bundles. The mitigation potential of the policy bundles was quantitatively evaluated in terms of vehicle kilometers traveled (VKT), exhaust emissions, and greenhouse gas emissions. The study also estimated the carbon emission intensity and consumer surplus for different mode users across all policy bundles. The findings from this showed that Policy bundle 4, a comprehensive mix of various policies, demonstrated a critical decrease in VKT and emissions compared with the other policy bundles and, thus, provided good scientific decision support for transport policymakers. The study helps Bengaluru's transport planning authorities in designing comprehensive mobility plans in a much more sophisticated way. The inclusion of public participation in the planning process helps improve sustainability. The consumer surplus provides a better understanding of social benefits derived from the policies, and emissions intensity estimates help understand whether the emissions have decoupled from the economic growth. The study also presents that public transportation plays a major role in solving congestion problems. Thus, it helps the planning authorities to prioritize their investments to make cities more liveable. [ABSTRACT FROM AUTHOR]

Biomass from agricultural production is a renewable energy source with a high-volatile content. Semicoke (SC) and gasification residual carbon, which are ultralow volatile carbon-based fuels (LVFs), are by-products of the coal chemical industry, which are over capacity and urgently need to be cleanly and effectively consumed. Biomass and LVFs exhibit complementary fuel characteristics, particularly the volatile content, which can potentially be coprocessed efficiently. Furthermore, oxyfuel combustion technology can not only realize carbon dioxide (CO2) capture and benefit from carbon neutrality, but also effectively reduce NOx emissions. The cocombustion of biomass and ultralow volatile fuel under oxyfuel conditions can both use individual benefits and effectively control pollutant emissions. However, the cofiring characteristics and interaction mechanisms of LVF with biomass in an oxyfuel atmosphere are yet to be fully understood. In this study, three ultralow volatile fuels and one typical biomass were selected to explore the oxyfuel cocombustion characteristics via thermogravimetric experiments. The experimental results indicated that blending with wheat straw (WS) improved the overall combustion performance, the ignition point was close to that of WS, and the burnout temperature was close to the average value of the two individual fuels. An increase in the oxygen content can effectively enhance the combustion feature of ultralow volatile fuels while it has little effect on the burnout performance of biomass. In the presence of high-content CO2 , the decomposition of carbonate in ultralow volatile fuel is impeded and the decomposition temperature is slightly increased. The present investigation can promote the efficient co-utilization of inferior LVFs and biomass, which also benefits CO2 capture, carbon neutrality, and even negative carbon emissions. [ABSTRACT FROM AUTHOR]

Considering CO2 emissions during production and re-mineralization during hardening, natural hydraulic lime (NHL) has been deemed an ideal cementitious material based on CO2 cycling. However, the preparation of NHL has rarely been reported. In this study, NHL clinker was prepared by calcining calcite tailings, and NHL was obtained by digesting the clinker. The results showed that the performance of the prepared NHL when calcining the calcite tailings at 1,200°C for 1 h and digesting the clinker at 20°C±2°C and 70%±5% RH (relative humidity) for 8 days met the requirements of NHL5 standard lime mortar. Furthermore, carbonation of the prepared NHL5 was studied, showing that the pore size of the hardened NHL5 mortar was refined during carbonation, and its compressive strength also improved. The prepared NHL5 could be an environmentally friendly cementitious material owing to its utilization of waste, relatively lower energy consumption, and higher CO2 recycling rate. [ABSTRACT FROM AUTHOR]

Buildings in high-rise high-density cities are principal contributors to global anthropogenic carbon emissions. Notwithstanding the many commitments to delivering low-carbon buildings (LCBs), various constraints have hampered their delivery. Despite their significance, very few studies have identified these constraints from the perspective of high-rise high-density cities. Furthermore, there has been no specific identification of stakeholders' engagement needed to address the constraints. The reported study addresses this gap by exploring the stakeholder engagement required to overcome the constraints of delivering LCBs. First, a list of 21 common constraints for delivering LCBs in high-rise high-density cities was identified by building on a precursor research study. In addition, 19 stakeholders with the ability to help overcome these constraints were identified through a literature review, and their engagement in addressing the identified 21 constraints was analyzed by employing social network analysis (SNA) approaches. This analysis was based on a two-round Delphi survey conducted with the participation of 15 experienced practitioners. The findings provide a systematic mapping of the constraints and associated stakeholders. Accordingly, clients, policy makers and regulators, property and facility managers, educational training and research institutes, and accreditation and standardization bodies showed an ability to address more than 60% of the identified constraints, whereas financial institutions, end users, project managers, and suppliers showed an ability to address less than 30% of the constraints. This study contributes to the theory by providing useful insights into developing and utilizing suitable SNA structures to analyze stakeholder engagement. It contributes to practice by identifying common constraints in delivering LCBs, identifying the significant stakeholders involved, and alerting industry practitioners to the imperatives and suitable modalities for their engagement to strengthen the delivery of LCBs in high-rise high-density cities. [ABSTRACT FROM AUTHOR]

This study uses recycled plastic (RP) as a fine aggregate in an attempt to minimize the waste on our planet. The results of the study suggest that the use of plastic in the construction sector does not only help minimize the production cost but also helps to increase environmental sustainability. In this study, the performance of a concrete mixture is evaluated based on seven different factors, namely: compressive strength, density, thermal conductivity, R-value, U-value, production cost (material and transportation costs), and eCO2 (embodied carbon dioxide) emission value. In line with the purpose of this study, a cost assessment, environmental assessment, and performance assessment have been carried out. Results indicate that as the plastic ratio increases, the compressive strength of the concrete decreases up to 35.16% in RP mixes. In particular, when 50% RP content is used, the lowest strength is obtained as 24 MPa. On the other hand, 50% RP content decreases the density and thermal conductivity to 2,200 kg/m3 and 0.458 W/mK , respectively. The results also reveal that increasing the RP content in the concrete mix reduces the U-value by 19.88% whereas 50% RP content increases the R-value up to 54.61%. The lower U value of RP indicates the ability of the material to resist heat flow and provides a better insulative value. In this research, cost and environmental assessments were also carried out. Based on cost calculations, RP4 showed the lowest cost because 50% of it is was composed of recycled plastic. Therefore, based on the cost analysis, it is the most beneficial element for use in a concrete mix. On the other hand, the use of recycled plastic leads to an increase in the carbon dioxide emissions while decreasing the amount of plastic waste for sustainability. [ABSTRACT FROM AUTHOR]

Climate change impacts on irrigated agriculture reveal the necessity of improving water and energy use efficiency and integrating renewable energies in this sector. Pressurized networks are typical in the irrigation sector. In these networks, nodes with excess pressure are frequent and the installation of pressure-reducing devices is required for their proper operation. As these devices imply an energy dissipation previously used, this work focuses on determination of the optimal number and location of pumps as turbines (PATs) in irrigation networks to maximize the energy recovery, provided that the feasibility of installation of each PAT separately is guaranteed considering the large flow fluctuations typical in these networks. The proposed methodology considered theoretical PAT curves and was evaluated in two irrigation networks located in Southern Spain. The results showed three and four potential sites for PAT installation in each network, with total annual energy recovery estimations of 43.1 and 91.8 MWh, a payback period lower than 10 years in most of them, and potential annual CO2 emissions savings up to 13.4 and 28.5 tCO2. The developed model could be an interesting tool to offer irrigation district managers or technicians a baseline hydropower potential scenario in irrigation networks. [ABSTRACT FROM AUTHOR]

The preliminary design and comparisons of major technical and economic indicators between a steel-ultrahigh-performance fiber-reinforced concrete (UHPFRC) composite truss (SUCT) arch bridge and a concrete-filled steel tubular (CFST) arch bridge with both spans of 375 m are carried out in this study. Compared with the CFST arch bridge, the SUCT arch bridge can improve the durability of the bridge and has advantages in terms of steel consumption, self-weight, carbon emission, and other indicators due to the use of UHPFRC with high compressive strength as the arch ribs to bear the large axial forces. Adoption of the cyclic construction method for the SUCT arch bridge with two closure processes results in a total cost basically equivalent to that of the CFST arch bridge. For the K-joints in the connection area of the UHPFRC arch ribs and steel web members, a new hybrid connection form of "perforated shear connectors (PBL) + headed studs" is proposed. Loading tests in three directions in plane, pull-out tests, and parameter analysis are carried out. The experimental results show that the new hybrid connector is reasonable for the K-joints, which has advantages of large stiffness, short force transmission path, and high efficiency, and can ensure the continuity of steel fibers. Moreover, the new hybrid connector displays good shear performance, pull-out performance, and high bearing capacity. Based on the results of parameter analysis, the sensitivity of the pull-out bearing capacity to the three variables is compressive stress in the arch rib, followed by the tensile and compressive strengths of UHPFRC. [ABSTRACT FROM AUTHOR]

The method of onsite pouring is mostly adopted in current construction of traditional frame beam (TFB) structures, bringing adverse effects like poor supporting timeliness, low concrete quality, hard-coordinated deformation, complex working procedure, high construction risks, and so on. In order to solve these problems existing in the structure and construction of TFB, a new type of prefabricated frame beam (PFB) structure was given a brief introduction of its design and feasibility. Based on a slope supporting project in Guizhou Province, China, main points and techniques in the construction of PFB structure were summarized. Differences as well as pros and cons in the process of onsite construction of two kinds of supporting structure were discussed and analyzed. Results and monitoring data showed that the PFB structure has advantages over TFB structures in terms of the construction period, personnel and machinery, safety management, economic costs, CO2 emissions, supporting effects, and so on. The feasibility and stability of PFB structures in high slope supporting projects were verified, which lays a foundation for the popularization and application of prefabricated structures in similar slope supporting projects. [ABSTRACT FROM AUTHOR]

Energy piles, a new type of heat exchanger that serves dual purposes, have gained increasing attention due to the growing energy demand and corresponding carbon emissions. Depending on intended operational requirements or by accident, energy pile groups may be subjected to cyclic and variable thermal loadings. This study presents the results from a series of full-scale field tests of a 2×2 energy pile foundation. The energy pile group was operated partially or fully during the tests to investigate the potential effects of cyclic nonuniform thermal loadings. The results indicated that the cyclic thermal loadings could induce an increase in compressive stress of piles at the end of the experiments. Further comparative analysis showed that the residual compressive stress was attributed mainly to the drag-down effects of the surrounding soil. The compressive stress induced by drag-down effects will overlap with the thermally induced stress, and thus lead to a more significant effect on the energy piles. If the drag-down effects are presented, the stress change may exceed the theoretical upper bound of thermal stress and may be underestimated. In addition, cyclic nonsymmetrical thermal loadings could induce accumulation of differential settlement and group tilt in the energy pile group. It was shown that the group tilt caused by cyclic and variable thermal loadings can be acceptable for general engineering structures. The group tilt will not accumulate further when subjected to symmetrical thermal loadings. A reasonable arrangement of operational piles still can be used to avoid unwanted group tilt generation. [ABSTRACT FROM AUTHOR]

Efforts are being made to achieve more efficient operation of buildings, with the goal of reducing the construction industry's contribution to energy consumption and greenhouse gas emissions. That contribution also includes the energy embodied in structures; that is, the energy consumed in the processes of extracting, manufacturing, transporting, and installing construction materials (including recycled materials) and elements. In particular, in spite of the use of additives such as fly ash, reinforced concrete (RC) structures, which are large consumers of cement, are responsible for a sizable proportion of worldwide carbon emissions. These emissions can be reduced significantly through the more efficient use of both concrete and steel that can be achieved by optimization. Modern optimization tools are now available that make it possible to perform large volumes of calculations efficiently that are applicable to a wide variety of structural engineering problems. This study presents an optimization approach developed with a view to allowing decision makers to balance sustainability and economic objectives. To illustrate this approach, an RC frame under gravity and lateral loads is considered in this paper. It was found that, depending upon the parameter values used in the calculations, the design optimized with respect to the footprint yields a footprint that is lower (by 5% to 10%) than the design optimized with respect to cost. The reduction can be smaller for low-rise structures and other structures with predominantly tension-controlled members. However, for structures whose members predominantly experience large compressive forces, such as high-rise buildings, the reduction may be more significant. This also may be true of certain prestressed and poststressed concrete members. Additional research aimed at ascertaining the extent to which this is the case is warranted. [ABSTRACT FROM AUTHOR]

A kinetic model of coal gasification in a Texaco gasifier was developed using the software Aspen Plus, and the model was validated using experimental data from previously reported research. The effects of the gasification temperature, use of steam (H2O) or carbon dioxide (CO2) as the gasification agent (GA), and the gasification agent/carbon molar ratio (GA/C) on the composition, net CO2 emissions, and H2/CO molar ratio of the resulting syngas were evaluated. The results showed that for both H2O and CO2 , CO was preferentially generated at high temperatures, whereas H2 and CO2 were dominant at low temperatures, although the carbon conversion was higher and the net CO2 emissions lower at high temperatures. On the other hand, the concentration of H2 was higher when H2O was employed as the GA, reaching 49% when the H2O/C ratio was 2.0, but the concentration of CO was higher with CO2 as the GA, reaching 72% at a CO2/C ratio of 2.0. The net CO2 emissions and the H2/CO ratio were lower with CO2 and higher with H2O as the GA. The concentration of CO in the syngas was the highest (72%) when the temperature was 1,600 K and the CO2/C ratio was 0.4, making it suitable as a raw material for the production of formic acid. The results of this study offer guidelines for the optimization of the operating parameters for entrained flow gasification and the application of H2O and CO2 gasification technology. [ABSTRACT FROM AUTHOR]

Geopolymer concrete is considered to be one of the best alternatives to portland cement concrete, partially or totally, not only because it decreases the CO2 emissions released during ordinary portland cement (OPC) production, but also due to its acceptable mechanical and durability properties. This study presents the experimental results of using fly ash (FA) and ground granulated blast-furnace slag (GGBFS) on fresh and hardened geopolymer concrete properties, considering the effects of several parameters such as binder type and content, alkaline binder ratio, molarity, Si/OH ratio, cement ratio in the binder, water addition, and curing temperature. These parameters were studied over a wider range than in previous research using local by-product waste to determine the validity of the additives for massive production of geopolymer concrete. The studied properties were the slump, 7- and 28-day cube compressive strength, tensile strength, and modulus of elasticity. For all studied mixes, the increase of the binder content, sodium hydroxide concentration, and cement ratio of the binder enhanced the concrete properties, whereas the increase of the alkaline binder ratio, Si/OH ratio in the solution, and additional water decreased the concrete properties. An increase of curing temperature from 30°C to 90°C improved the fly ash–based geopolymer concrete mechanical properties by an average of 35%; in contrast, the same increase in temperature decreased the concrete mechanical properties of GGBFS-based geopolymer concrete by an average of 22%. Equations for tensile strength and modulus of elasticity in terms of compressive strength were proposed and were compared with equations from standards and equations previously proposed in the literature. Finally, the environmental impact in terms of CO2 emissions was found to be on average 90% less than that of conventional concrete of the same grade. [ABSTRACT FROM AUTHOR]

The green loans program has continued to attract attention as an effective measure for promoting green retrofit to reduce energy consumption in old buildings. Various external factors negatively affect the decision-making process for the government and building owners. In particular, it is unclear how incentives and penalties take effect and to what extent they can influence the green loans program. Therefore, this study identified the influence of political factors, such as loan support and carbon taxation, on the strategic choices of the government and building owners. The results of this study showed that (1) as the supporting interest rate increases, both government and building owners are more likely to select a positive strategy; (2) as the carbon tax rate increases, both government and building owners are more likely to select a positive strategy; and (3) if the maximum supporting interest rate of 4.45% is applied, the greenhouse gas (GHG) emission reduction effect can be increased by about 3–5 times from the current level. It is not easy to achieve the national carbon emission reduction target for 2030 and 2050 only through green retrofitting of old buildings under the green loans program. Therefore, the government should develop an additional research and development budget and encourage developers to enhance the efficiency of green technologies. [ABSTRACT FROM AUTHOR]

A one-way traffic strategy is widely used in densely populated urban areas to improve traffic efficiency, but its environmental impacts remain largely unclear. This study investigated the effects of a one-way traffic strategy on vehicle emissions along a busy traffic corridor in Xi’an, China. This was done by integrating the traffic flow model calibrated by onsite traffic data and the emission model. The detour distance estimation method was proposed so that the emission trade-offs between increased vehicle miles traveled (VMTs) and improved traffic efficiency on one-way traffic corridors could be uncovered. Empirical results showed that one-way traffic cut down the total CO2 emissions by 11.8%, and reduced the CO, hydrocarbon (HC), and NOx emissions by 4.7%–25.0%. However, such emission reduction capacity gradually weakened and even completely dissipated with the increase of traffic demand on the corridor. When the road volume-tocapacity ratio (V/C > 0.87), one-way traffic was no longer a greener traffic organization. With the promotion of mitigation policies and technologies, one-way traffic is expected to further reduce CO2 emissions by 4.7%–10.9% and CO, HC, and NOx emissions by 8.4%– 41.1%. In addition, there was a total of 456 vehicles detours with an overall detour distance of 316.8 km, which resulted in a doubling of the emissions of detour vehicles. Although the implementation of one-way traffic brings environmental benefits, the detour problem should also be taken seriously. This study provides convincing evidence for understanding the emission changes on traffic corridors caused by one-way traffic conversion to support the promotion of eco-friendly traffic organization for realizing the goal of carbon peaking. [ABSTRACT FROM AUTHOR]

Emission of carbon dioxide (CO2) either from the firing of clay bricks or from cement production, contributes considerably toward global warming. Conversely, the production of bricks is inevitable since a large number of bricks are needed to fulfill the housing sector demand. In this study, silty clay-based geopolymer bricks were produced incorporating fly ash and sugarcane bagasse ash. This was accomplished in two stages: the laboratory phase that comprised of production of cylindrical specimens, and the industrial phase whereby full-size bricks were produced based on the results obtained in the laboratory phase. The silty clay-based geopolymer bricks were developed with lesser energy input, i.e., forming pressure of 7 MPa with curing at ambient temperature. The whole set of mechanical and durability properties of the newly developed geopolymer brick yielded satisfactory results conforming to the standard codes. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results revealed the coexistence of sodium aluminosilicate gel (N─ A─ S─ H) and calcium aluminosilicate hydrate (C─ A─ S─ H), which led to a dense microstructure resulting in increased mechanical strength and ensuring enhanced durability of the brick structure. The environmental impact assessment confirmed the ecofriendly utilization of sugarcane bagasse ash in combination with fly ash in clay-based geopolymer bricks. The newly developed geopolymer can have a broad range of applications, including wall panel making, jet grouting, deep mixing, mortar for masonry constructions, canal lining, and grouting material used in backfill grouting during shield tunneling. [ABSTRACT FROM AUTHOR]

Concrete with coal gangue as aggregate has a self-sensing ability with addition of carbon fiber (CF), which has an outstanding effect in terms of dealing with the large amount of coal gangue discharge and monitoring the concrete structure. However, studies on the development of CF-based gangue concrete (CF-GC) with self-sensing capabilities are limited. Therefore, the uniaxial compression tests of CF-GC were carried out and changes in the electrical resistivity (ER) and acoustic emission (AE) characteristics were monitored throughout testing. The test results suggested that the addition of CF can significantly improve the electrical conductivity properties of gangue concrete. Value of gage factor for CF-GC and gangue concrete is 2.3 and 16.6, which the value of gage factor for the CF-GC increased by 14.3 compared with the GC. The research showed a good correlation between the ER and AE of CF-GC, and an increase in curing time led to a decrease in in the electrical conductivity of CF-GC. This study shows that it is of great significance to be able to predict deformations in gangue concrete structures by monitoring changes in ER and AE. [ABSTRACT FROM AUTHOR]

When performing soil stabilization of soft clays, the effect of temperature on the properties of the stabilized material is usually not considered. In this study, the curing temperature development and its effect on the shear strength and stiffness of lime–cement stabilized Norwegian clays was studied by field measurements, laboratory tests, and numerical analysis. The study includes 18 samples cured under different temperatures and tested by uniaxial unconfined compression (UC) tests. By increasing the curing temperature of the stabilized soil, a significantly faster strength development and higher shear strength values were observed. Monitoring the temperature in the field and introducing the maturity number allowed for the calculation of the maturity of the installed piles. In combination with laboratory results, the use of a maturity number allows to estimate shear strength and the stiffness development of the installed columns. This may allow for a higher utilization of the stabilized material, which further on can lead to reduced amount of binder or a reduction of installed columns, giving reduced costs and carbon dioxide emissions associated with the installation process. [ABSTRACT FROM AUTHOR]

Peat is geotechnically problematic due to high organic content leading to low strength, high compressibility, high rate, and magnitude of creep. The nontraditional materials like a geopolymer can be used to stabilize the peat due to its low CO2 emission and high strength gain than traditional materials like cement. Therefore, this study presents the viability of rice husk ash (RHA)–based geopolymer to stabilize the Indian peat with a wide range variation of organic content (OC) (21%–79%) and fiber content (FC) (6%–73%). The geopolymer was prepared by adding extra aluminum oxide (Al2O3) with RHA to maintain the atomic weight of silica to alumina (Si/Al) equal to 3. The specimens with binder (RHA+Al2O3) percentages of 10%, 20%, and 30% by weight of dry peat and alkali/binder ratios of 0.5, 0.7, and 0.9 were activated by sodium hydroxide (NaOH) with molarities (M) of 3, 6, and 9. The results show that the RHA-based geopolymer stabilized peat depends on various factors like the amount of organic content in peat, amount of binder content, concentration of activator, A/B ratio, curing period, and pH. The optimum combination of binder content, concentration, and A/B ratio was found as 20%, 6 M, and 0.7 respectively. At this combination, the unconfined compressive strength (UCS) of treated peat was found 133, 125, and 136 times more than untreated sapric, fibric, and hemic peat, respectively. Further, it was observed that UCS decreases with OC and increases with the curing period The field emission scanning electron microscopy (FESEM) micrograph and X-ray diffraction (XRD) patterns confirm that the pore spaces are filled with cementitious products like zeolite which is further represented by a reaction mechanism. [ABSTRACT FROM AUTHOR]

As discussions around the circular economy (CE) start to move beyond Eurocentric approaches, US stakeholders are left with the mission of carving their way into CE. The US building sector has substantial impacts in resource use, waste generation, and carbon emissions, and a long way to go on the path toward CE. Circular building design involves strategies such as design for disassembly (DfD) to allow future repair, remanufacture, and reuse of building components, building adaptive reuse, and using salvaged materials in new construction. Although strategies like DfD have been discussed for the last 2 decades, they have failed to gain traction in building design. However, there is a limited body of literature devoted to understanding the barriers and enablers for key circular building design strategies like DfD. A few recent empirical studies in European countries have identified barriers for circular building design, which in this study were categorized according to their nature (regulatory, economic, technical, educational, cultural, technological, and environmental barriers). However, given the different regulatory, economic, and cultural contexts in which the US is situated when compared with European countries, the barriers identified in prior studies and their respective enablers may not apply to the US. For example, contrary to European countries, the US is yet to create a national CE-specific legislation or action plan. Thus, bottom-up efforts from industry stakeholders are key to achieve progress toward CE in the US. Yet there are no studies that investigated barriers and enablers to circular building design in the US context. This study aims to fill this knowledge gap. The authors interviewed architects across the US to understand the perceived and experienced barriers to circular building design in the US building sector and propose enablers to overcome these barriers. The barriers differed in nature from those found in European countries: although the share of technical and economic barriers were similar, more educational and cultural barriers were found in the US, as opposed to a larger shares of regulatory and technological barriers in European countries. The authors discuss the most mentioned barriers in the US (e.g., cost and schedule constraints, lack of clarity on what CE entails, and existing regulations and codes hinder reuse and repair), and the barriers that were new to the literature (e.g., belief that DfD compromises building durability and resiliency, conflicting goals between pre-engineered structures and future reuse, and the widespread use of nondurable building components). Finally, the authors propose enablers to address each barrier and discuss the role of different stakeholders in implementing enablers. Policymakers, non-governmental organizations (NGOs), industry associations, and researchers were the stakeholders with the highest leverage to enable CE in the US building sector. [ABSTRACT FROM AUTHOR]