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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]

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]

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]

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]

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]