Công bố quốc tế trong lĩnh vực kiến trúc, xây dựng (Tuần 3 tháng 7-2021)
Trong số này chúng tôi xin giới thiệu tới quý độc giả những nội dung chính của các công bố quốc tế đăng tải trên ScienceDirect và Springer Nature do Cục Thông tin khoa học và công nghệ quốc gia (NASATI) mua quyền truy cập như sau:
Quy hoạch đô thị:
– Nghiên cứu hệ thống thiết kế cảnh quan dựa trên công nghệ xử lý ảnh và thực tế ảo 3D
– Yếu tố xanh và không gian mở ở Vienna: công cụ chỉ đạo và đánh giá cơ sở hạ tầng xanh đô thị
– Đánh giá khả năng thích ứng của các loài cây đô thị trước tác động của biến đổi khí hậu: nghiên cứu điển hình ở Thượng Hải
– Sử dụng hệ thống thông tin địa lý để đo lường khả năng tiếp cận của các khu vực xanh ở trung tâm đô thị Nevşehir, Thổ Nhĩ Kỳ
– Thiết kế quản trị hợp tác cho các giải pháp dựa vào thiên nhiên
– So sánh các bộ dữ liệu mở toàn cầu và khu vực để lập bản đồ không gian xanh đô thị
– Phát triển công cụ định lượng để đo lường mức độ đáp ứng nhu cầu sử dụng không gian công cộng
– Tối ưu hóa không gian xanh đô thị dựa trên đánh giá rủi ro sức khỏe khí hậu – nghiên cứu điển hình của Bắc Kinh, Trung Quốc
Khoa học và công nghệ trong lĩnh vực kiến trúc, xây dựng:
– Phương pháp mô phỏng luồng không khí trong nhà dựa trên mô hình IFC (Industry Foundation Classes)
– Khung quản lý thông tin công trình tích hợp dữ liệu hiệu suất để xây dựng hiệu quả năng lượng vòng đời và thiết kế tối ưu hóa môi trường
– Tác động của nồng độ chất chống thấm nước đối với quá trình hấp thụ nước của vật liệu xây dựng
– Ảnh hưởng của cổng khuếch tán hơi đến hiệu suất giữ ẩm của tường khung gỗ
– Tối ưu hóa việc mô-đun hóa sơ đồ mặt bằng trong các dự án xây dựng theo mô-đun
– Tính toán hiệu suất năng lượng tối ưu về chi phí của một tòa khách sạn sử dụng mô phỏng động và thuật toán tối ưu hóa
– Biến đổi khí hậu và hiệu suất năng lượng của các tòa nhà trong tương lai – nghiên cứu điển hình cho các tòa nhà ở Vương quốc Anh
Vật liệu xây dựng:
– Tầm quan trọng và tiềm năng của vật liệu xenlulo và các dẫn xuất trong in bê tông 3D: Triển vọng và thách thức
– Đánh giá về độ bền của bê tông geopolymer cho các kết cấu và cơ sở hạ tầng bền vững
– Sử dụng xỉ hoạt tính MgO và bùn bentonit canxi để sản xuất vật liệu chắn dọc mới lạ
– Sử dụng geopolymer làm vật liệu đổ bê tông dưới nước
– Tính chất cơ học của xỉ hoạt hóa kiềm/bột nhão tro bay kết hợp với bùn trắng
– Thiết kế chất kết dính cao phân tử để cải thiện tính chất của xi măng magie photphat
– Bọt và đặc tính lưu biến của các polyme biến tính polydentat phosphonat trong xi măng
– Ứng dụng của bê tông tự phục hồi vi sinh: Nghiên cứu điển hình
– Hành vi thực nghiệm và mô hình số của các mối nối gỗ-gỗ composite (TTC),
Xin trân trọng giới thiệu!
QUY HOẠCH ĐÔ THỊ
1. Research on landscape design system based on 3D virtual reality and image processing technology
In order to ensure the rationality of landscape design, it is of great practical significance to simulate the planning effect. Aiming at the problems of two traditional landscape planning effect simulation systems, a new landscape planning effect simulation system was designed based on virtual reality technology. The overall framework of the system is composed of user layer, application layer and display layer. According to the system frame structure, hardware such as acquisition equipment, main control equipment, output and display equipment are selected; according to the system framework structure, the system software is designed to run the main program. In addition, this paper also based on 3D image processing technology landscape design system. In the design process, 3D landscape image can be preprocessed to remove noise information and redundant information, and 3D landscape image feature enhancement method is used to realize 3D landscape image feature enhancement and improve the clarity of landscape design image. Combined with the example of garden green space, according to the parametric plant modeling method, the morphological structure parameters of green plants are obtained, and the three-dimensional models of various plant modeling are established; the rules of parametric description of plant spatial layout are adopted, based on the open scene graph rendering engine, and the oculus rift virtual reality equipment is integrated to realize the virtual construction and display of three-dimensional garden vegetation landscape. The results show that the design effect of the system is very clear and of good quality. It has a high score in the design of courtyard landscape and garden landscape, and the system has low application cost, low energy consumption and high operation efficiency.
2. Mapping ecoacoustic hot spots and moments of biodiversity to inform conservation and urban planning
As the rate of urbanisation continues to increase, widespread habitat clearing within peri-urban landscapes contributes to significant environmental impacts, including loss of biological diversity. Acoustic recording has recently been identified as an effective tool for monitoring biodiversity and ecosystem health. With increasing pressure from urbanisation, it is critical that spatial and temporal variability in biodiversity is mapped across future development sites to enable sound decision-making and to deliver ecological urban design outcomes. This study used ecoacoustic monitoring to map biodiversity patterns in space and time to identify hot spots and hot moments of biodiversity activity across a peri-urban landscape in south-east Queensland, Australia. In this study, a hot spot represents an increase in acoustic activity at a given spatial location, whereas hot moments represent an increase in acoustic activity at a given time point. An acoustic index (Acoustic Complexity Index, ACI) was used as a proxy for biodiversity and visualised through spatial interpolation. The acoustic data were statistically modelled using Boosted Regression Trees (BRT). This approach enabled predictors related to acoustic complexity to be identified, including vegetation and landform. Results of this study have shown that ecoacoustic data can be used to map hot spots and hot moments of biodiversity and support more informed conservation decision-making in future urban planning frameworks, to avoid or mitigate negative impacts on biodiversity.
3. Green and open space factor Vienna: A steering and evaluation tool for urban green infrastructure
Due to the steady growth of cities and increased sensitivity to climate change, a rethinking of urban planning is required to manage resources efficiently and increase urban quality. Under current conditions, it is important to expand green and open spaces with all their green infrastructure and to optimize land use in terms of quality and quantity. There is a lack of tools for the specific control of urban green infrastructure at plot level. Furthermore, all previous attempts at green space factors (Berlin, Malmö, Seattle, Helsinki, etc.) have primarily focused on ecological factors. Climatic and especially social aspects provided by ecosystem services are largely ignored. It has also been proven that the existing tools do not adequately respond to different building typologies. The purpose of this paper is to present a new calculation method for a Green and Open Space Factor Vienna and to provide greater detail as regards computation, and to compensate for bias in the assessment. The Green and Open Space Factor Vienna considers selected ecosystem services of relevant green and open space elements, comprehensively integrating the ecosystem service approach into urban planning. Applying the new calculation method to the examples shows that this tool is able to capture changes in building mass. If the greening of building sites is relatively equal, the same values can be achieved. If only the building mass and not the proportion of greenery increases, the value of the Green and Open Space Factor Vienna deteriorates. The consideration of climatic, ecological, and above all social aspects in the Green and Open Space Factor Vienna as an urban development index is a promising approach for controlling the supply of green and open spaces, thereby supporting socially sustainable urban development.
4. Assessing the adaptability of urban tree species to climate change impacts: A case study in Shanghai
Urban forests and trees are affected by potential biotic and abiotic climate change impacts. To enhance urban forest adaptability and resilience to climate change impacts, tree species with high local climate adaptability and robust stress tolerance should be identified and selected. Climate events in the Shanghai area, such as late frost, chilling, heat waves, drought, typhoons, waterlogging, soil salinization, pests, and disease, directly or indirectly impact urban forests and trees. For urban tree species selection in the context of climate change, an assessment framework was proposed and applied to assess the climate change adaptability of 65 urban tree species in Shanghai using a method combined with quantitative data and qualitative descriptions. In this study, the climate types of tree species were divided into four groups according to annual mean temperature (AMT) and annual precipitation (AP): temperate, cool subtropical, warm subtropical, and moist subtropical species. The results showed that hardness, heat tolerance, chilling requirement, and drought tolerance were categorized as climate-related tolerances, while other tolerances were categorized as non-climate-related tolerances. The tree species’ optimal AMT and AP were significantly correlated with climate-related tolerances, but they did not respond to the non-climate-related tolerances. The warm subtropical species had higher stress tolerances than other climate types in the Shanghai area; therefore, the warm subtropical species with high tolerances were the most suitable alternatives for urban tree species selection with regards to Shanghai’s climate change impacts. This study also found that the AMT optimum is a better index to reflect tree species’ climate-related tolerances rather than the AP optimum. Finally, the adaptability assessment framework of climate change impact will offer guidance for future-oriented urban forest management and urban tree species selection in Shanghai.
5. Using geographical information systems to measure accessibility of green areas in the urban center of Nevşehir, Turkey
The problem of how to ensure the accessibility of green areas is a significant issue for urban planners and leaders. Every segment of society should have access to green areas. The 2015 United Nations General Assembly Resolution indicated the necessity of ensuring that children, older adults, and disabled people have equal access to green areas.
The Accessible Natural Greenspace Standard (ANGSt) was implemented in England in response to the United Nations 2015 Resolution. ANGSt states that housing developments needed to have a green space within 300 m in order to be identified as having adequate access to green space. Almost at the same time, Turkey has also identified increasing access to urban green spaces as a priority, which can be seen most directly in the 2014 Turkish Regulation on Spatial Planning. This document states that housing zones need to have a green space within 500 m to ensure that urban residents have sufficient access to green space. However, no specific suggestions or procedures have been provided on how to measure the accessibility of a city’s green areas. To fill this gap, this study developed a method for measuring the accessibility of green areas according to the standards outlined in the 2014 Turkish Regulation on Spatial Planning as well as the standards described in England’s ANGSt regulations. The accessibility of green areas in Nevşehir, Turkey was assessed using this method to demonstrate its utility.
The method of Comber et al. (2008) and the grid method used in the GEOSTAT procedure were adapted for this study to assess the accessibility of green areas in Nevşehir, Turkey. In order to conduct this study, ArcGIS was used and analyses were performed grid method. As a result, this study identified housing zones that do not have access to a green space, both according to Turkish standards as well as English standards. Furthermore, this study also identified many green spaces that are not within an accessible distance from residential areas, indicating that a significant proportion of Nevşehir’s green spaces are being under-utilized.
This study reveals that thus far, the planning approaches used in Nevşehir have not taken access to green spaces into consideration, particularly along the city’s borders. The center of the city has much more access to green areas, but it has the inverse problem of having green spaces that lack nearby residential areas, so they are not adequately utilized. This situation most likely arose due to reliance on the grid meter per capita standard for assessing green space rather than basing planning decisions on accessibility standards. Thus, this study provides important insights into Nevşehir’s current land use distribution that can be used to shape the future of urban planning in Nevşehir, while also providing a method for assessing land use distribution that can be used in a wide range of contexts to evaluate access to green spaces.
6. Designing collaborative governance for nature-based solutions
Urbanisation, population growth and climate change, among other challenges, have put pressure on urban infrastructure systems, prompting a shift from large-scale centralised infrastructure to localised nature-based solutions. Mainstreaming nature-based solutions requires a change in the planning and governance systems, and mediating new relationships and configurations between different actors through collaborative governance. Yet, limited guidance exists on how to design collaborative governance for delivering nature-based solutions. This has led to collaboration processes that are established on an ad-hoc basis, relying on the experiences, skills and viewpoints of their champions to endure. This paper synthesises and extends a suite of theoretical frameworks with the practice-based knowledge of urban practitioners across Australia (n = 42), to develop a framework for designing collaborative governance. The framework offers key principles and considerations for designing collaborations on nature-based solutions. It emphasises upfront planning that carefully considers the desired outcomes (the ‘why’), assesses the operating environment/context (the ‘what’), engages the right actors at the required level of influence (the ‘who’), and uses fit-for-purpose structures and process for interaction (the ‘how’). The framework also highlights that all those elements need to be considered with the intended level of impact in mind. To illustrate the application of our framework, we will use empirical examples from major urban development programs across Australia that have adopted water sensitive urban design (as part of the broader family of nature-based solutions) through cross-sectoral collaborations.
7. Residential urban trees – socio-ecological factors affecting tree and shrub abundance in the city of Malmö, Sweden
Trees and large shrubs in urban environments provide a wide array of ecosystem services, enhancing the well-being of urban residents. Public trees in Sweden are managed by local governments, but private-owned urban trees, which represent a large proportion of the total urban tree population, are managed by residential property owners. Residential urban trees are generally not included in urban forest management plans at local government level. This study examined property-level characteristics that could lead to better management decisions by property owners on residential trees in Malmö, Sweden.
Using spatial sampling, 99 properties were inventoried to determine tree basal area (m2/ha), as a measure of woody plant abundance. In parallel, residents were surveyed about their attitudes to trees, and information on background variables on their properties was collected using through publicly available spatial data. Statistical modelling was used to determine relationships between key socio-ecological variables and tree abundance as well as reasons for planting and removal of trees.
The results showed that positively perceived benefits of trees to property owners did not necessarily result in greater tree and shrub abundance on individual properties. Instead, house age and potential plantable space were the variables positively correlated with tree and shrub abundance. Years of residence had a negative correlation with probability of planting. The primary reason for tree removal was improper growing site, which indicates that providing practical information on appropriate site/species selection could reduce the risk of healthy urban tree removal.
8. The problem of suboptimal composition of urban trees in Warsaw
This study analyzes the planting decisions made by urban greenery managers in Warsaw between 2012 – 2017. The results showed that the species composition of planted trees was suboptimal. The tree species with higher dieback were planted more often than the tree species with relatively lower dieback. Moreover, the conducted econometrical analysis revealed that this important characteristic was not statistically significant for the planting decisions made by the urban greenery managers. A closer look at the functioning of the urban greenery management system in Warsaw revealed that this situation could potentially result from the phenomenon described in the agency theory as a principal-agent problem. Dieback was a feature difficult to include in the decision-making process in Warsaw without conducting nonobligatory and effort-intensive in situ studies. Meanwhile, the contract between the greenery managers (agent) and the city authorities (principal) was not “incentive-compatible”. It favored less effort-intensive decision-making, i.e. making planting decisions by greenery managers based on their intuition and experience, rather than on effort-intensive in situ analyses. The study suggests that the principal-agent problem should be further investigated as a potential barrier to optimal management of urban greenery.
9. A comparison of global and regional open datasets for urban greenspace mapping
Greenspace has positive influences on urban environment and human health, and thus it is desirable to acquire data for (urban) greenspace mapping. Nowadays, global and regional open land-use/land-cover datasets have become essential sources for greenspace mapping, but few studies have quantitatively compared them. To fill this gap, this study carries out a quantitative comparison of six global and regional open datasets (CGLS-LC100, CLC, GLC30, UA, FROM-GLC10 and OSM) for greenspace mapping. First of all, the most appropriate land-use/land-cover classes selected as greenspace are analyzed for each open dataset; then, different open datasets are evaluated and compared in terms of five measures (accuracy, precision, recall, F1-score and green coverage rate). Five urban areas in UK are chosen as study areas. Two categories of reference datasets are used for evaluation, including an Ordnance Survey (OS) greenspace dataset in UK and a number of sampling points classified by referring to Google Earth. Results show that: the OSM dataset performs the best, while comparing with the OS dataset (characterized by a narrowly interpreted greenspace); and the FROM-GLC10 dataset performs the best, while comparing with the sampling points (characterized by a broadly interpreted greenspace). Moreover, by using these two open datasets, most quantitative results are close to or higher than 80 %, in terms of the accuracy, precision, recall and F1-score; in most cases there also is the smallest difference between using these two open datasets and corresponding reference datasets, in terms of the green coverage rate. These findings have benefits for researchers and planners to choose an appropriate open dataset for greenspace mapping.
10. Developing a quantitative tool to measure the extent to which public spaces meet user needs
Public spaces acquire their value from their ability to meet users’ needs and requirements, and their contributing to people’s well-being and promoting quality of life. Although several studies have suggested methodologies and tools to measure certain features and elements of open spaces, a comprehensive quantitative tool to measure open users’ needs and requirements has not been issued. This study developed a quantity tool to measure the extent to which public spaces meet users’ needs and requirements. The tool was developed and implemented in four selected spaces in Sana’a city in Yemen. Space users, specialists in architecture and urban design, and experts in the field of the urban environment were involved in the development of the tool. Tool development has gone through the following validation processes; face validity, content validity index, construct validity of the tool, and internal consistency of items and factors. This study addresses a measuring tool that uses gap analysis index to determine the difference between the current level and the required level when public spaces meet users’ requirements.
11. Quantifying emotional differences in urban green spaces extracted from photos on social networking sites: A study of 34 parks in three cities in northern China
In rapid urbanization processes, the high density and fast rhythm of the urban living environment lead to mental tension, life pressure, anxiety, and other problems for people, which facilitates negative emotions. Studies have confirmed that an urban green space is a “restorative environment” that can effectively alleviate negative emotions and improve moods. Social media data can be objectively quantified to evaluate people’s emotional responses to urban green spaces. Based on the analysis of social media data, this study examines whether there are differences in emotions linked to locations, with the data extracted from microblogs similar to Twitter in three different cities. Seven emotions (happiness, fear, surprise, anger, disgust, neutral, and sadness) were identified using online cognitive services on photos collected from microblog data. Three emotion-based indexes (emotion intensity index, emotion intensity index, emotion evenness index) were used to expand the urban green space pair from the spatial perspective of research on the influence of emotion. The results show that there are significant correlations among age, gender, emotional diversity, area, accessibility, NDVI, and emotion. The results also show that (1) the higher the NDVI of urban green space, the greater the probability and intensity of emotion in green space, and the more happiness emotion people show. (2) there is a significant positive correlation between urban green space area and EEI, and a significant negative correlation between urban green space area and EPI, EII, which is just opposite to the NDVI results. (3) Optimistic and positive emotions are widely expressed in cities, and happiness is expressed most and strongly. The negative emotions such as fear, anger, and trouble are less expressed, and the expressions of emotions in cities are highly similar. With the increase of age, happiness emotion increased, and sadness emotion decreased.These results show that the urban green space planning can be used to intervene in the expression of human emotion based on where a person lives. In the future, the planning and design of urban green spaces based on the reasonable balance and combinations of area, accessibility, and the NDVI can enhance the emotional enthusiasm for these areas. Improving the planning and design of the existing urban parks and green spaces with positive intervention methods can provide a feasible solution to meet the growing population’s emotional recovery needs.
12. An optimized evaluation method of an urban ecological network: The case of the Minhang District of Shanghai
Obtaining the characteristics of an urban ecological network structure and connectivity plays an important guiding role in the concrete implementation of ecological construction in a space. Resistance assignment is a key step in ecological network construction. However, most research ignores the diversity of land use in an urbanization environment and the difference between ecological space centres and boundaries. Taking Minhang District of Shanghai as an example, this paper puts forward an optimal evaluation method for an urban ecological network. By combining the morphological spatial pattern analysis method and graph theory, the resistance value of different urban land uses was evaluated, and the ecological network was constructed by comprehensively considering the land use types, land area, forms, and positions. The connectivity and the importance of individual nodes at four different thresholds were quantified. The results revealed that the core and the edge areas of the morphological spatial pattern analysis occupied the highest amount of space, 33.34 % and 21.92 %, respectively. In addition, there were relatively few large and high-quality ecological spaces, and the green space was seriously fragmented in the study area. The degree of structural connectivity was related not only to the area proportion of the ecological space but also to the area of connected patches. The contribution value of each node to the overall network connectivity was affected by the mobility of the species, the node area, the spatial location, and the surrounding matrix environment. This study provided a framework designed to optimize the evaluation method of an urban ecological network. The influence of the type and structure of urban land use on the resistance value was analysed in a more detailed way, and the results of the connectivity and the important nodes were obtained more accurately.
13. The value of the shading function of urban trees: A replacement cost approach
Cooling is one of the most important benefits of street trees, yet city planners lack estimates of the value of this benefit. Estimation of the value of the cooling effect could help to strengthen the case for investment in a tree cover as a part of the urban infrastructure for climate change adaptation. This article aims to address this research gap by presenting a novel application of a replacement cost method using the costs of parasols for estimating the value of shade provided by urban trees. Using the method, we calculated the net present value of the shade from a generic tree and used these estimates in a case study in Prague, Czech Republic. The results showed that the costs of tree planting and maintenance were higher than the estimated shading benefits in the short term (20–30 years), but the situation reversed when the tree life expectancy increased (> 40 years). Street trees are hence a long-term investment in terms of microclimate regulation. The proposed approach can assist city planners with an assessment of microclimate regulation by urban trees as it can be easily applied with local data, and can complement other methods to show the wider benefits of urban trees.
14. Regional effects of plant diversity and biotic homogenization in urban greenspace – The case of university campuses across China
The human introduction and spread of species in urban greenspace may lead to an increase in the similarity of plant species composition between distant areas. Univervsity campuses are an important element of greenspace in many cities, but we know little about the extent to which such biotic homogenization of plant species can be detected across different regions and plant growth forms. Here, we collected plant species occurrence data from 253 Chinese university campuses in 130 cities to explore patterns and drivers of plant diversity and biotic homogenizations across different geographical regions and growth forms. We found that native species richness was positively correlated to campus area at the national scale, while non-native species richness was significantly associated with mean annual temperature, precipitation seasonality, campus area and campus age. We found limited support for homogenization caused by non-native plants in most regions. For growth forms, tree species exhibited significant biotic homogenization at the national scale, with weak or no effect for shrubs or herbs. Plant compositional similarity varied among regions, and eastern China always had the highest similarity in species composition with other regions. Combined effects of mean annual temperature and geographic distance overshadowed the roles of other predictors in shaping compositional dissimilarity in most regions. These findings suggest that multi-region settings and plant growth forms should be considered in urban biodiversity management, with special attention towards avoiding homogenization in trees. Increasing native species with local characteristics and considering region-specific environmental and socio-economic conditions are beneficial to mitigate biotic homogenization in urban greenspace.
15. Urban green space optimization based on a climate health risk appraisal – A case study of Beijing city, China
Urban heat islands (UHI) and global climate change pose serious threats to human health, making health risk appraisal of urban space as well as the planning and improvement of green space important research projrcts. Meteorological sites, satellite images, electronic maps, questionnaire survey data, statistical yearbooks, ArcGIS spatial analysis technology, MATLAB matrix analysis technology, remote sensing inversion, and ground-object extraction technology were used in this study to evaluate how changes in Beijing’s urban thermal environment influence the health of residents. A genetic algorithm was used to optimize the simulation of green space, based on which, different measures were proposed to improve planning. The results show that areas of greater UHI impact on respiratory diseases, cardiovascular diseases and emotional health are mainly concentrated south of the North Second Ring Road in central Beijing. Furthermore, low-level influence areas are highly connected and clustered, while the high-level influence areas are distributed in clusters. The intelligent optimization and simulation of green space show that it exhibits a spatial distribution potentially with building green wedges and cooling corridors. Based on apprasial on health risk impact, analysis on health and climate zone, as well as optimization and simulation of green space, measures such as cooling nodes, urban blue axes, green rings, pergolas, and ventilation corridors are proposed to improve the comfort of urban living environments as well as reduce risks associated with health and environment.
16. Variance of the impact of urban green space on the urban heat island effect among different urban functional zones: A case study in Wuhan
The urban heat island effect (UHI) is frequently observed in cities, and is associated with environmental effects. Urban green space (UGS) has been shown to play an important role in mitigating the UHI. However, impacts from the spatial pattern of UGS among different urban functional zones are largely ignored. This study established a spatial regression model to reveal the relationship between landscape metrics of UGS and land surface temperature (LST), in order to characterize the different effects of the spatial pattern of UGS on UHI among urban functional zones. The result shows that the proportion of UGS and shape complexity metric show a general negative impact on LST both overall and in individual urban functional zones; while none was found with aggregation, the fragmentation metric and connectivity. An area-related metric can be used to explain LST in public service zones and has a negative impact on LST. The research proves that UGS in different urban functional zones play different roles in mitigating the UHI effect. The cooling effects are related to the spatial pattern of UGS. Accordingly, it is recommended to consider the different roles of the spatial pattern of UGS in different urban functional zones in mitigating UHI for a liveable environment.
17. Green roof ecosystem services in various urban development types: A case study in Graz, Austria
In this paper, we describe how different urban development types and environmental conditions could affect the broad distribution of green roofs in Graz (Austria). A GIS-based mapping method was applied along the lines of four ecosystem services (i.e., regulation of microclimate temperature regulation, support of air quality improvement support, stormwater retention and biodiversity enhancement). The results are rather positive and indicate that green roofs are fit on 87 % of the investigated roof area (172 out of 203 buildings) based on roof dimensions and constructional measures. Among the investigated roof area, 63 % was classified as having a ‘high need’ for greening and, thus, a need to generate ecosystem services in urban environments. These results present a paradox: Roofs on block and row development are more appropriate for greening purposes than roofs on historical perimeter block development, but the latter is often found in environments where green roofs are needed more (i.e., inner-city centres). Therefore, city planners should consider using different greening strategies for distinct urban development types under diverse environmental conditions and prioritise the greening actions accordingly. These findings may be relevant in other historically grown, centrally compact European cities.
18. A simple and easy method to quantify the cool island intensity of urban greenspace
Accurately and easily quantifying the greenspace cool island intensity (GCII) is important to understand the cooling effect of urban greenspace for better urban greenspace planning and management. This study proposed two new methods (i.e., equal area method and equal radius method) to estimate GCII and compared them with two old methods (i.e., turning point method and fixed radius method) in terms of the GCII magnitudes, spatial variations, relationships with greenspace size, and the estimation of optimal greenspace size in cooling the environment (i.e., threshold value of efficiency (TVoE)). We performed the analysis based on Landsat derived land surface temperature (LST) in seven Chinese cities with varied climate background and geographic variations. The results showed that: (1) Different methods significantly impacted the estimated GCIIs with higher values by the turning point method and lower values by the equal area method. (2) GCIIs by different methods were positively and significantly correlated with each other and characterized similar spatial heterogeneities. (3) GCIIs by all methods showed significantly positive logarithmic relationships with greenspace area with higher R2 observed by the equal area method. (4) The four methods estimated close TVoEs with no significant difference among them. We recommend the equal radius method to quantify GCII for its equal effectiveness but easier calculation compared to other methods.
19. Assessing the performance of urban open space for achieving sustainable and resilient cities: A pilot study of two urban parks in Dublin, Ireland
The urban environment is at increased risk of unforeseen disturbances associated with climate change and urbanisation. Urban open space, when appropriately located, designed and managed, can potentially support underlying ecosystem services and provide multiple social-ecological benefits. Conversely, poor planning or design can result in mono-functional open space with potentially negative results for the built environment. To anticipate future uncertainty and create more sustainable and resilient cities, it is important to assess the performance of urban open space. This paper provides a deeper understanding of resilience at the scale of open space within the urban fabric and suggests a framework conceptualising resilience with an emphasis on ecosystem services and spatial configuration. A hierarchical index system (HIS) comprising twenty-six measurable indicators and an associated assessment methodology is proposed to evaluate the performance of urban parks in terms of their contribution to urban resilience and sustainability. The applicability of the HIS and assessment methodology is examined in a pilot study by assessing two urban parks in Dublin, Ireland. This paper contributes to the coupling of resilience thinking with urban design by proposing an evaluation method that assists design professionals and urban decision-makers in evaluating the performance of existing schemes and new proposals for urban open space. This paper will help a range of stakeholders better understand the settings of these spaces through scientific evidence.
20. Landscape index for indicating water quality and application to master plan of regional lake cluster restoration
Understanding the relation between landscape pattern and water quality is essential to making a master plan for restoration of regional lake and wetland clusters, which has not yet been well resolved. Here, we studied the impacts of landscape pattern changes on water quality over lake clusters, taking the aquaculture area in the Lixia River hinterland of China as a case. Multi-temporal Landsat series of remote sensing data from 1985 to 2018 was used and space-for-time substitution (SFTS) method was applied to explore the relationship between landscape pattern and water quality. Results showed that wetland and free water surface were the dominant classes of the lake cluster in 1985 and 1990, but they began to rapidly decrease from 1995 to 2000. The enclosure aquaculture increased rapidly since 1995 and became the dominant class between 1995 and 2018. The patch density of aquaculture water (PD_A) increased from 0.09n/km2 in 1985 to 0.34n/km2 in 2018, with the largest degree of fragmentation in 2000. However, the growth rate of PD_A declined significantly after the enactment of the lake ecological protection policies. The SFTS results showed that PD_A had positive correlation with total nitrogen (TN) (r = 0.26), ammonia nitrogen (NH3-N) (r = 0.21), and Chlorophyta (r = 0.33), and the water quality degraded with increasing PD_A. Hence, PD_A could be a water quality indicator of lakes in the Lixia River hinterland. The study is expected to provide a viable method to design regional restoration plan for degraded and over-developed wetland areas.
21. Green urban garden landscape design and user experience based on virtual reality technology and embedded network
Available online 29 June 2021, 101738
With the development of electronic science and technology, green landscape planning and design in urban landscape design has become a new trend and direction. The emergence of virtual reality assisted design technology and platforms has brought more innovation space for landscape designers and greatly reduced Time and workload. The mature application of virtualization technology and embedded network technology in various fields provides technical support for perfecting the concept of virtual reality. Based on virtual reality technology and embedded network, this thesis discusses green urban garden landscape design, and constantly strengthens user experience, expands the extension of garden landscape design. On the one hand, the development of virtual reality technology and embedded network makes garden landscape design the imagination of the teacher can be brought into play and realized. On the other hand, in the virtual scene, the landscape architect integrates the characteristics of different types of elements to design creative and innovative, open and shared garden landscapes. Using the Internet platform as a medium, refer to and learn from more representative works, and stimulate more creative landscape design concepts.
KHOA HỌC VÀ CÔNG NGHỆ TRONG LĨNH VỰC KIẾN TRÚC, XÂY DỰNG
1. Improving the energy flexibility of single-family homes through adjustments to envelope and heat pump parameters
With the increase of fluctuating renewable resources both on the grid and locally on buildings, a need arises for buildings to be flexible such that their energy demand can be modified to match energy generation. This study aims to characterize key approaches to increase the flexibility of a single-family home subject to a number of climate conditions. The home is modeled in TRNSYS in 5 climates, and building thermal mass, heat pump characteristics, and water heating setpoints are adjusted to assess the impact of each on the building’s flexibility. The key metric used to assess flexibility is the cumulative absolute residual load over a year, where the residual load is defined as the difference between the average hourly demand of electricity and the average hourly available electricity. A control scheme is employed to implement demand response, but overall energy demand and thermal comfort are also considered throughout the year to assess effectiveness of the demand response approach. Results presented on 21 variations to the base house show the benefit of thermal mass in maintaining thermal comfort while changing thermostat setpoints and demonstrate the benefit of variable speed heat pumps for meeting available electricity supply. In the best case, a 36% decrease in residual load over the year is found for a simulation in Gaithersburg, MD compared to the base case. Results from this work suggest best approaches to take when developing new housing stock if consideration is needed for how well the buildings can respond to fluctuations in energy generation from intermittent sources such as wind and solar.
2. A performance data integrated BIM framework for building life-cycle energy efficiency and environmental optimization design
Data-driven green building design in BIM is challenged by the lack of a comprehensive data integration framework with the capabilities of building life-cycle performance data management and application. This paper proposes a performance integrated BIM (P-BIM) framework for building life cycle energy efficiency and environment optimization. A school building is presented as a case study to verify the P-BIM framework and the design optimization workflow established. The results show that the optimization can improve IEQ by 11.5% and reduce LCC by 36.8%. The influences of different envelope constructions on indoor environment, energy consumptions, and costs are also studied. The P-BIM framework and the optimization methodology built on it demonstrate that the methodology developed can expand the application scope of BIM and contribute to data-driven green building design. More application scenarios focusing on the stage of facility management and different sustainability performance will be conducted in P-BIM framework in future works.
3. Simulation method for indoor airflow based on the Industry Foundation Classes model
Indoor airflow is an important factor affecting indoor thermal comfort and human health; it is also an important consideration for architectural design, ideal living environments, and green building fields. Currently, most building models required for indoor airflow simulation have been manually created by researchers, which is inefficient and error-prone in modeling. To overcome this problem, this study examines the similarities and differences between the general standard data model Industry Foundation Class (IFC) in the BIM (Building Information Model) and the spatial grid required for indoor airflow simulation and proposes a conversion method from an IFC model to spatial grid. This method uses the rich semantic, geometric, and relational information in the IFC model to automatically extract building interior space, divide numerical calculation grid, and map semantic attribute information to the spatial grid. On this basis, an integrated simulation framework is constructed with OpenFOAM to simulate the airflow movement of the indoor space of the building. The simulation results show that the method used in this study can automatically construct the spatial grid using existing IFC models without re-modeling, which provides important support for indoor airflow modeling. In addition, the integrated simulation framework connects model construction, simulation analysis, and other steps through tool chain. This process simplifies the simulation operation, provides convenience for indoor airflow simulation, is conducive to the wide use of indoor airflow simulation in architectural design and architectural design optimization, and also provides reference for related numerical simulation research and digital city modeling.
4. Production of lightweight mortar using recycled waste papers and pulverized ceramics: Mechanical and microscale properties
The development of new composites using eco-friendly materials is the new trend of ensuring sustainability of construction materials. This study aimed at the development of lightweight mortar using recycled waste papers and pulverized ceramics, which is a foreseen energy-efficient and eco-friendly constructions process. Standard mortar samples of 40 × 40 × 160 mm were fabricated by varying aggregates contents (waste papers, pulverized ceramics and river sand) at 0, 25, 75 and 100%. The study determined the suitability of the samples produced by examining the physical properties (water absorption and densities), mechanical properties (compressive strength and flexural strength), and microscale/mineralogy tests (Scanning Electron Microscopy, X-ray diffraction, and X-ray fluorescence). A 26% increase in flexural strength was observed with 100% ceramics as aggregate in concrete, and the same mix possessed lesser water absorption properties. Overall, the study established that pulverized ceramics and moderate paper aggregates are suitable for sustainable mortar production. Results of this study will serve as a guide for the developer of cementitious composites.
5. Impact of water repellent agent concentration on the effect of hydrophobization on building materials
It is desirable to avoid or lessen moisture-related problems in building components exposed to wind-driven rain via correct material design and/or choice. In some cases however – e.g. for historic building facades – the only possibility is to modify the hygric properties of existing materials. Hydrophobization treatment is suggested as a possible protocol, but the proper concentration of the water repellent agent to achieve the expected effect is still open to discussion. This study proposes the novel concept of a material-dependent critical agent concentration: the lowest concentration that ensures hydrophobic effectiveness on a specific material. For validation, the hygric impact of hydrophobization treatment at different agent concentrations is studied. Specifically, a balanced mixture of silanes and siloxanes is used as the agent, and eight experiments are performed on ceramic brick, lime mortar and sintered glass. Results demonstrate the existence of a material-dependent agent concentration. Only when treated above it will the hygric properties be significantly modified. Moreover, hydrophobization impacts the capillarity of a material much more than its hygroscopicity, due to the difficulty for the large molecules of water repellent agents to penetrate into fine pores. The bulk density, open porosity and pore size distribution are typically only minimally influenced.
6. Experimental research of a membrane roof with the membrane eccentrically fixed on a thin-walled open-profile supporting contour
This paper presents experimental research about operation of a square-shaped membrane-type sag roof on a flat supporting contour. Membrane roofs include a thin metal shell (membrane) attached to the supporting contour. The membrane has the functions of structural support and protection, mainly resisting the stretching force. The supporting contour resists the compression force by bending in two planes. Eccentric fixing of the membrane in the contour gives rise to a torque. With torsion, the thin-walled open-profile contour develops additional normal tensions. Experiments were conducted on a test bench consisting of a base, a model and instrumentation. The membrane model is convertible: the same model can be used to represent four structural setups. The test have examined the effects of a load uniformly distributed over the surface of the roof, and of focused loads: vertical loads applied to the membrane (to emulate the effect of a suspension crane), and horizontal loads applied to the supporting contour (to emulate wind loads and loads created by support bridge cranes). Parameters of the test structure are such that they enable emulation of roofs spanning over 24 × 24 m and 36 × 36 m. The model’s dimensions in plane are 3 × 3 m, with the supporting contour shaped as a channel bar welded of L-bar. The membrane roof model is manufactured of aluminum alloys. The paper places the main focus on the operation of a model with a membrane fixed eccentrically (to lower ledge of the channel bar) to the supporting contour. Performance of such roofs has been experimentally confirmed; the test revealed significant reserves of structural bearing capacity, small horizontal and vertical displacements of the supporting contour, and admissibility of plastic deformations in small sections of the contour. Experimental data are compared with calculated results from the computing system model. The calculations are carried out taking into account the constrained torsion of thin-walled open-profile rods.
7. Effect of vapor diffusion port on the hygrothermal performance of wood-frame walls
Vapor diffusion ports (VDPs) that are drilled in the exterior sheathing of wood-frame walls are commonly used in wood-frame buildings in the coastal region of British Columbia with the intention to improve the drying capacity of wood-frame exterior walls. This practice originated following the systematic building envelope failures due to rain penetration that occurred in this region around 1985–1995. A previous laboratory study found that VDPs provided substantial improvement in the drying rates of OSB sheathed walls, but not for plywood sheathed walls. A more recent laboratory test using wood-frame walls with higher insulation levels in compliance with the current energy code found that VDPs did not significantly improve the drying rates. To provide a more comprehensive evaluation of the effect of VDPs, hygrothermal simulations using WUFI 2D are carried out based on the recent tests. The WUFI 2D model is firstly validated with measurements from the recent tests and the validated model is then used for a parametric study to evaluate the effect of VDPs under three wetting scenarios using yearly weather data for Vancouver. It is found that VDPs have the ability to improve the rate of drying, which is directly related to the moisture content level of the wall assemblies, although the improvement is moderate even for high moisture levels. The contribution of VDPs to reducing mold growth risk is insignificant under a moderate moisture load and becomes considerable only under a sustained high level of moisture load, i.e., east orientation with an ongoing rain infiltration. Therefore, efforts should be made towards properly designing and constructing building envelope details instead of relying on VDPs as a mitigation measure to improve durability performance.
8. Time-dependent reliability analysis of recycled aggregate concrete cover cracking induced by reinforcement corrosion
A time-dependent reliability analysis of the cover cracking of recycled aggregate concrete (RAC) induced by reinforcement corrosion was conducted in this investigation. The existing models were summarized, and then the model of Zhang et al. was validated to determine the time corresponding to the cover cracking of concrete. Then, a corrosion current density of 0.068 μA/cm2 for the reinforcement in the concrete was specified when the concrete components were exposed to outdoor conditions without an accelerated corrosion process. Parametric studies were undertaken, and the results indicated that the considered factors, i.e., RAC compressive strength, ratio of concrete cover depth to rebar diameter, corrosion rate, rust expansion ratio and porous zone thickness, have significant effects on the probability of failure. Finally, the results show that the probabilities of failure of cover cracking and reaching the limit crack width are 3.34 × 10−2 and 6.64 × 10−2, respectively.
9. Optimizing the modularization of floor plans in modular construction projects
This paper presents an optimization model that enables construction planners to generate and analyze optimal tradeoffs between minimizing the total cost of modular construction projects and maximizing the functional performance of the floor plan. The model is developed in three main stages that are designed to formulate the model decision variables, objective function, and relevant constraints; implement the optimization computations using linear programming; and evaluate the model performance using a case study of a modular construction project of an office building. The results of the case study highlight the original contributions of the model to theory and its impact on practice. First, the model contributions to theory include its novel capabilities of quantifying the impact of room widths and lengths on the total modular construction cost and floor plan functional performance, identifying an optimal width and length for each room in modular construction projects from a range of feasible alternatives, and generating optimal tradeoffs between the two conflicting objectives of minimizing modular construction cost and maximizing floor plan performance. Second, the results of the case study highlight the impact of the model on practice and its ability to provide planners with much-needed support in optimizing the layout of modular construction projects in order to maximize floor plan functional performance while minimizing the total modular construction cost including its fabrication, transportation, assembly, and structural frame costs.
10. Analytical and numerical study of double-panel confined masonry walls
Masonry is a traditional construction method in Algeria. It is commonly used in the construction of walls, such as bearing walls or infill panels between columns and beams. Several factors make it difficult to take the material into account in structural analysis, especially in seismic cases. Therefore, engineers usually consider the masonry panel as a nonstructural element. However, the contribution of the masonry panel on the behavior of a building cannot be ignored, particularly, when talking about confined masonry walls. For this reason, a great deal of research has been conducted to generate a database that allows for masonry walls to be considered in the structural analysis. The present paper aims to contribute numerically and analytically to the study of the behavior of double-panel confined masonry walls. Thus, some of the most used analytical models are used to predict the strength and the stiffness of those structures. Moreover, a numerical micro model has been selected from the literature and validated using original experimental tests. Furthermore, one of the most used simplification strategies was adopted. The paper concluded with suggesting some analytical models and with proving the effectiveness of the numerical adopted model to simulate the behavior of confined masonry walls under Pushover tests and finally, the paper recommends future seismic study.
11. Evaluating the vertical cooling performances of urban vegetation scenarios in a residential environment
Vegetation is one of the effective measures to mitigate urban heat island (UHI) and improve thermal comfort. Many existing studies have investigated the cooling performance of vegetation on the pedestrian level. However, no study explores the cooling effect of vegetation on other heights. In this research, we evaluate the vertical cooling performance of different vegetation species (grass, shrubs, trees) in the residential quarter using the ENVI-met model. The results show that different vegetation types have important effects on the thermal environment based on the same green coverage rate, and different vertical cooling performance of different vegetation types are also different. The study found that among the three common vegetation types (trees, shrubs, and grass), the cooling effect of trees is the most significant, and the vertical cooling performance is the best, followed by shrubs. The maximum cooling value of the tree to Ta and MRT is 0.49 °C and 17.7 °C respectively. The presence and increase of shade have a direct effect on improving the local and even the overall thermal environment. Therefore, when designing residential green space, this study suggests that designers should not only focus on the green coverage rate but also pay attention to controlling the shaded area. This research provides a new perspective for investigating the cooling effect of vegetation and provides scientific guidance for the design of residential quarters.
12. Synergistic effects of ettringite-based expansive agent and polypropylene fiber on early-age anti-shrinkage and anti-cracking properties of mortars
Effects of the ettringite-based expansive agent (EA) and polypropylene (PP) fiber on early-age anti-shrinkage and anti-cracking behaviors of mortar are comprehensively investigated in this paper. Combined with mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) analyses, its mechanism of the combination of EA and PP fiber on shrinkage and cracking restriction behavior of mortars is also proposed. The results indicate that the drying shrinkage resistance and cracking resistance behavior of the specimens with the combination of EA and PP fiber, are better than those of the specimens with single EA and PP fiber, while their residual expansion strain in autogenous shrinkage is lower than that of the specimens with single EA. The results of MIP and SEM analyses confirm that the formation of self-compressive stress generated by reinforcing effects of PP fiber and well three-dimensional network structure of ettringite distribution during expansion stage will partly offset the shrinkage force during shrinkage stage. Therefore, the combination of EA and PP fiber is prone to create a non-cracking shrinkage-compensating concrete in real construction.
13. Cost-optimal energy performance calculations of a new nZEB hotel building using dynamic simulations and optimization algorithms
This paper presents the procedure for conducting cost-optimal energy performance calculations for a new nearly zero energy hotel building in Croatia in the context of Energy Performance of Buildings Directive 2010/31/EU. For this purpose, dynamic simulation models of building and its technical systems were developed in IDA ICE simulating tool and coupled with GenOpt optimization software.
Annual energy performance of the building is assessed by running hourly simulations. Energy, equipment and installation works costs were obtained by the open market analysis. After that, the global cost function was derived, and optimization performed to minimize the costs. The results show that the preferred heat source at the cost-optimal level of the building energy performance is air-to-water heat pump coupled with gas condensing boiler. Furthermore, an analysis of thermal comfort is provided to demonstrate the use of the proposed approach in preventing system oversizing, efficiency decrease and thermal comfort deterioration. At the end, energy performance calculations obtained by IDA ICE were compared to those obtained by the widely used EN 13790 and EN 15316 series of standards used for determining energy performance of buildings for legal purposes. Based on this, the recorded discrepancies in results are analysed and applicability of mentioned standards calculations on low-energy buildings is discussed.
14. Rice husk cement-based composites for acoustic barriers and thermal insulating layers
This work evaluates the performance of cement-based composites made with rice husk and intended to be used in acoustic barriers and as thermal insulating material in a multilayer system. Because acoustic barriers are exposed to external conditions and mechanical loads, a wide range of laboratory tests were performed to evaluate the mechanical, durability and acoustic characteristics of the composites. Their specific heat capacity and thermal conductivity were evaluated when used as an insulation layer. Other cement-based composites that incorporate treated wood and rubber granules were studied for comparison purposes. The environmental performance of these new cement-based composites was evaluated by means of a life cycle assessment (LCA). It was found that those that contain rice husk are suitable for coating acoustic barriers, since it offers a good mechanical, durability, and acoustic performance. It was also found that rice husk cement-based composites can be used as thermal insulation layer. The LCA further demonstrated the good performance of the rice husk composites compared with those containing treated wood and rubber granules.
15. Climate change and the energy performance of buildings in the future – A case study for prefabricated buildings in the UK
Climate change – partly driven by the increasing level of anthropogenic greenhouse gases – is affecting the energy consumption of buildings. This study assesses the impact of climate change on the energy performance of buildings. It focuses on the energy consumption associated with heating in a case study of prefabricated building in the UK.
The energy consumption associated with space heating is evaluated using the degree-days theory, and the actual energy consumption of the buildings is used to verify the outcome of the analytical degree-days approach for the estimated energy consumption. The verified degree-days model is then used to predict future energy demand of the case study building in 2030, 2050, and 2080 using two climate change scenarios with medium (A1B) and high (A1F1) emissions. In addition, the energy-related CO2 emissions associated with the space heating are evaluated using carbon intensity projections. This study identified the true heating base temperature for the case study building and this allows for the estimation of the future energy consumption of the building with an average 6% margin of error. For the prefabricated case study building, the energy consumption associated with heating in 2030 and 2080 is expected to be up to 12% and 34% lower than in 2017 respectively. Moreover, the outcomes of this study showed that the standard base temperature of 15.5 °C for the degree-days method is significantly higher than the actual heating base temperature of the prefabricated building by 2.5 °C.
16. Exploring the user performance of Korean women in smart homes with a focus on user adoption
The penetration of smart homes into households in South Korea is fast growing and is predicted to reach a domestic market value of up to seven billion US dollars by 2026. However, the factors affecting user adoption and influencing successful performance are not adequately considered in the current delivery of smart housing. This research aims to explore user adoption by women in South Korea based on their current experience of the smart features delivered in their smart home units. An intensive interview targeting female residents in their thirties and forties who were the dominant occupiers and users of smart homes was conducted. The results from the intensive interviews provided three principle findings. First, the three steps of user adoption (awareness, opportunity and experience) were not adequately achieved by users, which led to unsatisfactory approaches to living in the smart home. Second, a lack of pre-instruction and guidance led to poor knowledgeability in the application, which negatively affected the opportunity and experience of smart features. Third, many smart features in the contemporary smart home are not users’ preferred brand or product type. User preferences and needs are neglected in current top-down delivery systems, which negatively affect the satisfaction levels of users. This study reveals the significance of the three steps of user adoption to achieve optimal user performance through an alternative delivery strategy. The provision of a new approach to smart housing delivery that adequately considers users’ preferences and needs is required to achieve the successful user performance proposed in this study.
17. Microencapsulated bio-based phase change material-micro concrete composite for thermal energy storage
The quest and interest shown towards developing organic phase change materials (PCMs) for thermal energy storage (TES) applications in buildings are gaining momentum in recent years. From this perspective, the present study aims at developing a novel microencapsulated bio-based phase change material (MbP) integrated in to a micro concrete composite (MbPMC) for thermal energy storage in buildings. The MbP and MbPMC were experimentally characterized in terms of their morphological, thermal and structural properties. The surface morphology results signified that, the as-prepared MbP particles being formed were near-spherical in shape with sizes ranging between 2 μm and 10 μm. The highly crystalline nature of the bio-based PCM chains and the amorphous structure of the shell material were confirmed through the X-ray diffraction analysis. The Fourier transform infrared (FTIR) spectra has further confirmed the chemical stability between the core (PCM) and the shell material. The MbP has exhibited congruent phase change behavior with a good latent heat potential of 47.31 J/g. Besides, the MbP was found to be thermally stable, commencing from the operating temperature of 35 °C up to 150 °C, as confirmed through the leakage and thermogravimetric tests. A unique and optimized sequential operation of mixing the ingredients for preparing MbPMC matrix was established with a view to obtain the best end product. The as-prepared MbPMC has exhibited adequate structural integrity with a compressive strength of 38.78 MPa at a MbP dosage of 0.075% by the weight of cementitious materials added in the mix. Ultrasonic pulse velocities (UPV), along the directions orthogonal to the direction of pour of the concrete specimens, were observed to be very close, thus proving that the densities, across the cross section of the specimen are more or less uniform. For incremental dosages of MbP, the trend observed in the indicative compressive strengths of MbPMC specimens from rebound hammer tests was observed to be similar to the trend observed in the compressive strength values obtained from the compressive testing machine (CTM). In total, these test results have revealed the ability and stability of the MbP incorporated micro concrete composite (MbPMC) for achieving thermal energy storage and passive cooling in buildings without sacrificing its structural integrity.
18. Modern heavyweight concrete shielding: Principles, industrial applications and future challenges; review
Heavy weight concrete (HWC) is one of the most used artificial materials for the embodiment of special infrastructures such as nuclear power, medical, nuclear science and industrial facilities. The review highlights the main aspects of HWC covering the general concept of radiation physics, fundamental of geometrical design for radiation attenuation and recent advances of HWC technology. An overview of recent research and development of HWC for various applications in engineering and radiation attenuation is elaborated. Besides, the primary industrial applications, future challenges and current limitations of research and development of HWC are also deliberated. Recent works had established that the degree of attenuation of biologically harmful forms of radiation, such as gamma-rays and X-rays, is proportional to the atomic mass (Z) of the shielding material. The high penetration power enables the radiations to penetrates the living bodies and causes harmful ionization of the biological cells. Therefore, the concrete material capable of effective attenuation of these rays plays a critical role in ensuring the safety and health of personnel in nuclear facilities. A comprehensive analysis of the literature shows the limitations in the present body of knowledge associated with the use of more than one type of nano-materials to achieve a virtually impervious HWCs. Besides, a significant gap was identified on the method of improving the cost efficiency of HWC by the use of byproduct heavyweight aggregates or by adding more than one type of aggregate and inclusion of heavyweight fiber. The review had established several critical areas for future works covering cost optimization in the formulation of high-quality HWC, reactive powder and geopolymer HWC, combinations of nano-materials, crack control and elevating Z-value of HWC to improve harmful radiation attenuation performance.
19. Life cycle assessment of a south European house addressing building design options for orientation, window sizing and building shape
The life cycle assessment (LCA) methodology has been extensively used to assess the environmental influence of alternative building construction; however, the influence of building design has seldom been assessed for Mediterranean climate. This article aims to evaluate the influence of three, often neglected, design options on the life cycle (LC) energy and environmental impacts of a south European single-family house: solar orientation, window sizing, and building shape. Using a parametric attributional LCA, the house’s materials, construction, maintenance, and operation (heating and cooling) are analysed for different design scenarios. Annual operational energy, LC non-renewable primary energy (NRPE) and environmental LC impact assessment (LCIA) results are presented and discussed. Results show that embodied energy generally surpasses operational energy. Building orientation has less influence on LCIA results than on operational energy, particularly for compact shapes. Scenarios with bigger Window-to-Wall Ratio (WWR) have higher embodied impacts, being more sensitive to orientation due to solar gains. Lower WWR (5%) can be used to reduce the overall LC impacts, especially in houses with lower operational patterns. A compact shape building was shown to reduce heating impact, while a terraced and less compact shape reduces cooling impact. Compared with literature, this study reveals that, from a LC perspective, design options are as significant as construction options. Finally, design recommendations should be based on LCA and not only on operational results; nevertheless, a LCA single indicator (NRPE or Global Warming Potential) can be used to support decisions for alternative house designs with similar construction.
20. An empirical study of green retrofit technologies and policies for aged residential buildings in Hong Kong
Given the ever-increasing number of aged residential buildings in Hong Kong, green retrofit provides a sustainable solution for improving existing aged residential buildings’ performance instead of constructing new buildings. Studies on green retrofit technologies (GRTs) and green retrofit policies (GRPs) have received great attention globally. However, few studies have been done to understand the applicability and importance of GRTs and GRPs, and the impacts of GRPs on the application of GRTs in a particular region, such as Hong Kong. Therefore, based on a questionnaire survey conducted in Hong Kong, this study aims to further examine the GRTs and GRPs that have been identified in a previous study. The applicability of the GRTs and the importance of the GRPs for green retrofit of aged residential buildings in Hong Kong were studies, the correlations between the GRTs and GRPs were analyzed, and a priority guide was developed for promoting green retrofit of aged residential buildings in Hong Kong. The findings can help various stakeholders to have a better understanding of the GRTs and provide valuable references for the local government to develop future GRPs. Furthermore, this study also provides a fundamental guide for future green retrofit research and development in the local and global contexts.
21. Evolutionary artificial intelligence approach for performance prediction of bio-composites
Construction and Building Materials, Volume 290, 2021, 123254
Abstract: Giving the high amount of carbon and energy emission from the use of traditional building materials, the use of bio-composites made from industrial crops especially hemp has caught attention from researchers in recent years. These bio-composites not only enhance the thermal performance of buildings but also promote sustainable development due to their eco-friendly nature. Due to their highly heterogeneous nature, however, most of the existing studies on the bio-composites have only focused on experimental investigations, while mathematical modeling of physical, thermal and mechanical properties of bio-composite remains a challenge for the researchers. In this paper, an artificial intelligence (AI) based gene expression programming (GEP) technique is used to develop the mathematical models for predicting the dry density, compressive strength and thermal conductivity of hemp-based bio-composites. A large amount of database was established based on past studies and the most influential parameters were identified by several trial analyses. The proposed mathematical models showed a high correlation with the experimental results. All the models passed the statistical and performance index checks showing strong predictability, generalization capability and high accuracy of GEP-AI models. Comparison of results with the regression analysis techniques further proved the superiority of GEP-AI models over the traditional methods.
VẬT LIỆU XÂY DỰNG
1. Accelerated weathering resistance of high-density polyethylene composites reinforced with microcrystalline cellulose and fire retardants
In this study, high-density polyethylene (HDPE) composites reinforced with microcrystalline cellulose (MCC) and fire retardants, ammonium zeolite (AZ) and mono ammonium phosphate (MAP) were exposed to ultraviolet (UV) radiation using an accelerated weathering test chamber for total of 672 h. The weathering effects on the surface characterization and morphology of the composites were examined with Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), color, gloss and surface roughness measurements. Furthermore, tensile and flexural tests were determined after the weathering exposure. The results showed that the weathering of composites led to changes on the investigated properties. As a result of surface roughness measurement, the highest Rz (mean peak-to-valley height) values were obtained from the composite surfaces of the HDPE/AZ10 (86/10, w/w) and the HDPE/MCC/MAP10 (71/15/10, w/w). The SEM studies confirmed that AZ addition resulted in some protrusion at the composite surfaces while MAP addition caused some coarsening on the composite surfaces. After the weathering, the decrease in mechanical strengths of the samples was found as 32%. The overall mechanical properties were not considerably affected with 672 h of the weathering exposure.
2. Ground granulated blast-furnace slag/fly ash blends activated by sodium carbonate at ambient temperature
Construction and Building Materials, Volume 291, July 2021, 123378
Alkali-activated materials (AAMs) with low carbon emission acted as a potential alternative for Portland cement. To further reduce the CO2 emission, FA and weak base were proposed. However, the strength development of slag/FA blends activated by sodium carbonate (NC) seemed unacceptable for actual engineering application. In this study, the strength of slag-FA blends activated by NC at ambient temperature was systematically studied, and the various fineness slag and activators dosage were used; hydration flow and chemical shrinkage was used to analyze the hydration process; the hydrates were characterized by XRD, TGA, SEM and 29Si NMR; the pore structure was characterized by MIP; the pH value and sodium ions were tested. Results showed that lower slag fineness and higher dosage of NC significantly shortened the induction period of slag hydration and promoted the formation of C-(N)-S-A-H and calcite. Moreover, due to the higher hydration degree of slag, FA was continuously activated over time. It seemed that NC-activated slag/FA activated blends showed an excellent mechanical property, and the compressive strength was up to 55.5 MPa and 63.8 MPa at 28 d and 90 d. The research suggested the experience for the design of weak base-activated slag/FA.
3. Development of high performance carbonatable concrete for steel slag valorization
Construction and Building Materials, Volume 39, July 2021, 123317
This study presents a high performance carbonatable concrete (HPCC) for the valorization of large volume steel slag. HPCC mix is designed to possess closely-packed particle size distribution, in which steel slag accounts for 90% of the binder. HPCC mix exhibits high flowability with ease of workability. The compressive strength of HPCC mix after appropriate predrying treatment reaches 104.9 MPa and 173.7 MPa, respectively, after 12-hour and 7-day carbonation curing. This can be attributed to the additional densification from the precipitation of carbonation products to the already densified matrix, which can be visually and quantitatively illustrated from the examination of microstructure and pore characteristics, respectively. HPCC mix exhibits negligible moisture absorption which is comparable to ultra high performance concrete (UHPC) mix, indicating high resistance to the ingress of foreign deleterious agents. Moisture absorption of Carbonation-induced deformation of HPCC mix is much smaller in comparison to UHPC mix, and the volume stability of HPCC mix is improved as a result of the consumption of f-CaO and periclase during carbonating. Therefore, HPCC mix is a promising candidate for effective utilization of steel slag while maintaining a high performance.
4. Importance and potential of cellulosic materials and derivatives in extrusion-based 3D concrete printing (3DCP): Prospects and challenges
Construction and Building Materials, Volume 39, July 2021, 123281
Three-dimensional concrete printing (3DCP) is an emerging digital construction technique, thwarted by critical issues related to its material design and preparation. These problems demand innovative and sustainable solutions. Cellulosic materials (CMs) are the most bountiful natural polymers and are superb starting materials for the large-scale manufacturing of sustainable chemicals and derivatives. This article presents innovative ideas for the viable use of CMs and derivatives in extrusion-based 3DCP (E-3DCP). In the light of a detailed literature review, the CMs and derivatives were critically analyzed based on their attributes, and potential combinations along with their limitations, possible side effects, and incompatibilities with other raw materials and admixtures currently used in E-3DCP. The potential efficacy of CMs and derivatives in E-3DCP may have been overlooked. Accordingly, a structured classification of CMs and derivatives is proposed for E-3DCP. CMs and derivatives offer sustainable ways to be used as fine aggregates, reinforcements, and cement replacements. Besides, these also offer practicable internal curing and alternative shrinkage mitigation applications. Furthermore, these could be used in numerous multiple combinations with other materials to derive complementary benefits. Importantly, CMs and derivatives could significantly improve cost-effectiveness through mix design optimization choices, and their use in lightweight E-3DCP structures. Finally, recommendations are drawn as benchmarks for future research and development. Therefore, an increased yet optimized use of CMs and derivatives could lead to revolutionary applications of E-3DCP.
5. Utilization of non-metalized plastic bag fibers along with fly ash in concrete
Construction and Building Materials, Volume 39, July 2021, 123329
The continuous production and dumping of plastic waste cause a serious impact on environmental pollution. Deploying of plastic waste in construction products reduces environmental pollution and also minimizes construction and dumping cost. This paper examines the mechanical, durability and impact attributes of concrete prepared with non-metalized waste plastic bag fibers (NMWPF) and fly ash (FA). Ten mixtures were designed in which five mixtures were Ordinary Portland cement (OPC) based including NMWPF content of 0, 0.50, 0.75, 1.00, and 1.25%. Remaining mixtures were FA blended mixes having same percentage of NMWPF content as that of OPC based mixtures, wherein 20% of cement was swapped with FA. The addition of NMWPF together with FA in concrete reduced the requirement of superplasticizer dosage. The compressive strength of both OPC and FA-based concrete reduced by the addition of NMWPF at all curing ages. However, FA-based concrete (prepared with and without NMWPF) exhibited better compressive strength than OPC based concrete at 90 days curing. The addition of NMWPF together with FA in concrete significantly augmented flexural strength, split tensile strength and resistance to abrasion, impact and drying shrinkage. Though resistance to water penetration decreased on the addition of NMWPF in both OPC and FA-based concrete, the FA-based concrete (prepared with and without NMWPF) performed better than OPC based concrete. Moreover, statistical analysis showed that most of concrete characteristics were predominantly affected by NMWPF. Overall, this research revealed positive results on using NMWPF along with FA in concrete and paved the way for further researches in same field.
6. Development and characterization of a new multi-strength level binder system using soda residue-carbide slag as composite activator
Construction and Building Materials, Volume 39, July 2021, 123367
A new multi-strength level binder system was developed as a potential replacement of cement. It utilized alkaline solid wastes soda residue (SR) and calcium carbide slag (CS), to synergistically activate ground granulated blast-furnace slag (GGBS) and fly ash (FA). A comprehensive combination of experimental studies on compressive strength, setting time, fluidity, chloride-ion consolidation, and drying shrinkage with XRD, TG-DTG, FTIR and SEM-EDS examinations ensured a systematic evaluation of properties and evolution mechanism of the proposed binder. The results show that mixing CS can increase the early hydration rate and generate more C-S-H gel and Friedel’s salt, Hydrotalcite crystal products. As a result, the early and late strengths were significantly improved. The chloride-ion consolidation rate was increased, and the drying shrinkage was reduced. On the other hand, FA’s low activity was used to adjust the strength level. Also the FA can reduce shrinkage, but it hindered the consolidation of chloride ions. The new binder system had a 28d strength of 17.5–43.2 MPa, with the initial and final setting times of 3.8–6.1 h and 6.4–10.2 h, respectively. At the water-to-binder ratio of 0.5, the mortar’s fluidity was 146–181 mm, the drying shrinkage was 0.11%–0.29%, and the chloride ion consolidation rate exceeded 70%. This new binder system can be applied to concrete blocks, pavement bricks, slope protection concrete, and other unreinforced products. The results obtained are instrumental in mitigating the environmental pollution caused by industrial solid wastes and reducing binders’ cost.
7. Effect of waste marble powder and rice husk ash on the microstructural, physico-mechanical and transport properties of foam concretes exposed to high temperatures and freeze–thaw cycles
Construction and Building Materials, Volume 39, July 2021, 123374
An experimental program was performed to evaluate the impact of rice husk ash (RHA) as cement replacement and waste marble powder (WMP) as sand replacement on the microstructural, mechanical and transport properties of foamed concrete exposed to high temperature and freeze–thaw cycles. For this, Portland Cement (PC) was replaced by RHA at 10% and 20%wt of binder and silica sand was replaced by WMP at 25% and 50%wt of fine aggregates to cast foamed concrete mixtures. Two different foam contents of 40 kg/m3 and 80 kg/m3 were used in the production of foamed concretes with water/binder (w/b) ratio of 0.70. Two reference mixtures were produced from silica sand and without RHA at each foam content. Other foam concretes were fabricated from 25% and 50% WMP instead of silica sand and 10% and 20% RHA instead of cement. Fresh properties of mixtures were evaluated by performing slump test. Transport properties of foam concretes were investigated, including porosity, sorptivity and water absorption after 90 days curing. Mechanical properties of foam concretes were investigated, including compressive and flexural strength ultrasonic pulse velocity (UPV) after 7, 28 and 90 days. Drying shrinkage and thermal conductivity of concretes were also studied after 90 days. Durability of concretes were also investigated after exposure to the temperature of 200, 400, 600 and 800 °C and freeze–thaw (F-T) cycles of 100 and 200 in addition to microstructure investigations. Results show that 10% RHA as cement substitute and 50% WMP as sand substitute give optimum percentage especially at late-age of 90 days at foam content of 40 kg/m3. The lowest drying shrinkage and sorptivity were obtained by using 10%RHA and 25%WMP. The results also indicate that water cooled specimens showed more strength loss than air cooled specimens after 200 °C. The worst F-T performance was obtained for the mixture containing 10% RHA and without WMP by 43.8 and 59.8% strength reductions.
8. The impact of carboxylic acid type hydrophobic agent on compressive strength of cementitious materials
Construction and Building Materials, Volume 39, July 2021, 123315
Abstract:: One of the most effective methods to improve durability of cementious materials is resist the intrusion of water born aggressives by mixing with hydrophobic agent, limiting the development of compressive strength. In this study, effect of carboxylic acid ammonium salt hydrophobic agent on compressive strength of cementitious materials is examined and its mechanism is analyzed. It is investigated that the impact of hydrophobic agent on hydration degree, amount and structure of hydration products shows that hydrophobic agent has little influence on hydration and products. In contrast, the generation of calcium carboxylate and increase of air content will cause loose of the microstructure of cement pastes confirmed by electrical conductivity and zeta potential. The secondary stress is proposed to analyze the effect of microstructure change on the compressive strength. The result of this study shows that hydrophobic agent might have great sense to improve durability of concrete and the compressive strength reduction should be considered.
9. Fabrication of superhydrophobic bilayer composite coating for roof cooling and cleaning
Construction and Building Materials, Volume 291, July 2021, 123283
Building energy consumption is an important part of energy consumption. Cooling materials can be applied to reduce building energy consumption. In this study, chromium trioxide (Cr2O3) and titanium dioxide (TiO2) were introduced into low-density polyethylene (LDPE) matrix to prepare the solar-infrared reflective layers, then styrene–butadiene-styrene triblock copolymer (SBS) and surface functionalized nano-silicon dioxide (SiO2) superhydrophobic coating was constructed on the surface forming bilayer composites applying for building roof. It was found that SBS/SiO2 coating had higher roughness, which provoked a soaring contact angle of about 160° realizing superhydrophobic surfaces. Withal, the contact angle was invariant nearly 160° after dropping the solution of calcium chloride (pH = 6), acid (pH = 2), and alkali (pH = 13) on the surface, which engendered chemical stability and anti-pollution property. Subsequently, the emissivity of LDPE and 10 wt% Cr2O3 composites coated with SBS/SiO2 coating (LDPE/Cr-10/S) as well LDPE and 10 wt% TiO2 composites coated with SBS/SiO2 coating (LDPE/Ti-10/S) were increased to 83% and 83.9% along with high near-infrared reflectance was 47% and 63.1% separately. Simultaneously, when the initial temperature was 24 °C for 1 h under strong light irradiation in indoors, the final temperature of glass was 69 °C while the finished temperature of LDPE/Cr-10/S and LDPE/Ti-10/S were reduced to 30.5 °C and 25.8 °C respectively, showing the excellent cooling property.
10. Developing cold-mixed epoxy resin-based ultra-thin antiskid surface layer for steel bridge deck pavement
Construction and Building Materials, Volume 39, July 2021, 123366
To improve the skid resistance of epoxy asphalt-based concrete (EAC) pavement, a cold-mixed ultra-thin antiskid surface layer (UTASS) was developed and incorporated into the EAC pavement in this study. The performances of four types of epoxy resin-based binders were assessed. The best binder type was selected and UTASS preparation procedures were determined. Subsequently, the skid resistance, high-temperature rutting resistance, low temperature cracking resistance, and interlayer bonding properties of the EAC-UTASS composite structure (with the UTASS on the top of the EAC) were evaluated using a series of tests, and the performances of EAC-UTASS were compared with several other composite structures that are commonly used in the steel bridge deck pavement (SBDP) in China. The results showed that the texture depth of EAC-UTASS is almost 10 times of that of the pavement composite structures with an EAC surfacing structure. In addition, EAC-UTASS has excellent high-temperature rutting resistance, low-temperature cracking resistance and interlayer bonding stability. Finally, a stripping resistance test was utilized to evaluate the UTASS based on a third-scale Model Mobile Loading Simulator (MMLS3). The service life of UTASS was determined based on the anti-stripping coefficient threshold value of 80%. Based on the results in this study, the use of the UTASS was found to be a feasible strategy for enhancing the skid resistance of EAC pavement.
11. Advanced lightweight periclase-magnesium aluminate spinel refractories with high mechanical properties and high corrosion resistance
Construction and Building Materials, Volume 39, July 2021, 123388
A new strategy to improve the mechanical strength and the cement clinker corrosion resistance of refractories for cement kiln was proposed in this work. For this purpose, advanced lightweight periclase-magnesium aluminate spinel refractories (LPSR) with high mechanical properties and excellent cement clinker resistance were fabricated using microporous magnesia aggregates. Their microstructures and properties were then compared to conventional dense periclase-magnesium aluminate spinel refractories (DPSR) containing sintered magnesia aggregates. The apparent porosities of the microporous and dense magnesia aggregates were 43.1% and 5%, respectively. Scanning electron microscopy observation results showed that the interface between the microporous aggregates and the matrix was better, which significantly improved the strength and thermal shock resistance of the LPSR. Additionally, the microporous magnesia aggregates absorbed some of the penetrating slag from the matrix, which prevented further infiltration. Thus, after substituting the microporous magnesia aggregates for dense magnesia aggregates to fabricate LPSR, the practically same cement clinker resistance was obtained for the LPSR compared to DPSR. Meanwhile, the bulk density was decreased from 2.87 g/cm3 to 2.61 g/cm3, while the compressive strength and flexural strength increased from 48.7 MPa to 73.1 MPa and 6.0 MPa to 10.1 MPa, respectively. Meanwhile, practically the same cement clinker resistance was obtained for the LPSR compared to DPSR.
12. A state-of-the-art review on the durability of geopolymer concrete for sustainable structures and infrastructure
Construction and Building Materials, Volume 39, July 2021, 123381
The need for sustainable and environmentally friendly concrete for construction has resulted in the development of low carbon concretes such as geopolymer concrete. Geopolymer concrete replaces cement with industrial waste materials i.e., utilizes fly ash and slag for its mixture along with the addition of a small quantity of alkali activator required for the geopolymerization process. There is a large number of articles published on the mix proportion, workability, strength and material properties of geopolymer concrete (GPC) in the last 15–20 years. However, research on the durability of the reinforcing steel in various types of geopolymer concrete is limited and found to be contradictory with ordinary portland cement concrete (OPC) in literature. This paper presents a critical and updated review of the literature on the durability of GPC published between 1990 and 2020. A simple and systematic methodology including Preferred Reporting Items for Systematic Reviews (PRISMA) and Meta-Analyses procedures were adopted with modifications for this review. The review is divided into six key sections after the introductory section to have a holistic understanding of the durability of GPC and to highlight gaps for future research. The first section presents the review of recent articles that purely investigate the development of microstructure of various types of GPC. The second section reviews studies on the repairs of reinforced concrete by GPC. The third section covers articles on the durability of GPC against acids, chlorides, freeze and thaw, and temperature effects. The fourth section reviews studies on the structural performance of GPC specimens when subjected to corrosive environments. The penultimate section reports gaps, opportunities and potential areas of future research on the durability of GPC. Finally, the conclusions summarise the findings of the review.
13. Using MgO activated slag and calcium bentonite slurry to produce a novel vertical barrier material: Performances and mechanisms
Construction and Building Materials, Volume 39, July 2021, 123365
Slag-cement–bentonite (SCB) slurry has been widely used for the construction of vertical cutoff walls to restrain the movement of groundwater at contaminated sites. However, the conventional cement-based slurry needs a long time to evolve satisfactory performance along with a relatively high environmental load. This paper proposes an innovative material for the self-hardening slurry system, consisting of reactive MgO, slag, bentonite and lots of water. The properties of fresh slurry, unconfined compressive strength (UCS) and permeability of the MgO activated slag and bentonite (MASB) slurry are investigated in comparison with SCB slurry. The results indicate that compared with SCB slurry, MASB slurry with appropriate proportions has comparative fresh properties, but possesses higher UCS and much lower hydraulic conductivity (close to 1.0 × 10−10 m/s) at a later age. A massive formation of expansive hydration products (hydrotalcite phases) could satisfactorily fill in the voids of matrix, leading to a dense microstructure which is responsible for the excellent mechanical and penetrative performance of MASB slurry. The overall findings from this study well demonstrate that the developed MASB slurry holds great potential as a novel, eco-friendly and cost-effective material in the construction of vertical cutoff walls.
14. Geopolymer as underwater concreting material: A review
Construction and Building Materials, Volume 39, July 2021, 123276
Underwater concrete is one of the special types of high-performance concrete in the current industry which is commonly used to construct bridges, dams and structures whose foundation is built underwater. In contrast with typical concrete, the implementation of concrete underwater requires different techniques due to the different concrete properties in order to ensure successful implementation. A new material called geopolymer is now widely promoted for its ability to replace ordinary Portland cement (OPC) as a binder due to its green technology. Numerous researches have established that the geopolymer has comparable strength and chemical resistivity compared to OPC. However, to date, only limited researches had been conducted to examine the use of geopolymer as an underwater concreting material. From the review that has been done, it can be concluded that the requirements for underwater concreting material should include washout resistivity, workability and durability in addition to high strength. This review highlights that the geopolymers are proven to provide excellent strength, durability and workability in accordance with the EFNARC standard. Finally, future research opportunities are also presented in this review with regards to the potential of geopolymer in replacing OPC as underwater concreting material.
15. Chemo-mechanical properties of alkali-activated slag/fly ash paste incorporating white mud
Construction and Building Materials, Volume 39, July 2021, 123312
Abstract:: White mud (WM) is a waste solid from paper industry. It mainly contains calcium carbonate and residual alkali metal ions (e.g., K+, Na+ and Mg2+). The aim of the study was to test the feasibility of incorporation white mud into a blended slag/fly ash alkali activated binder system. Blends of slag and fly ash was used as the precursor and WM was used as the filling material. Pastes with 0%, 10%, 20%, 30%, 40% and 50% WM were prepared for the investigation. It was found that the compressive strength decreases with the WM content increasing. Nevertheless, the paste containing 50% percent of WM is still comparable with Portland cement 42.5. Besides, XRD, TGA, FTIR, SEM/EDX tests were performed. The results indicated that the main reaction product of AASFW is a C-(N)-A-S-H type gel, and the formation of hydrotalcite is promoted as the increment of white mud replacement. In the end, nanoindentation reveals that the addition of WM leads to the histogram of both elastic modulus and hardness shifts towards lowers values. This supports the observation at meso-scale. It is expected that the current study provides an insight into the alkali activated slag/fly ash/white mud binder material and offers a sustainable solution for effective utilization of WM.
16. Design of polymeric binders to improve the properties of magnesium phosphate cement
Construction and Building Materials, Volume 291, July 2021, 123202
In the context of reducing the environmental impact of cement manufacturing, magnesium phosphate cements raise interest as alternative binders in construction, for immobilization of wastes, and recycling purposes. Their use in applications is somehow limited by short setting time, brittleness and low water resistance; this calls for the use of additives. Two polymer additives were designed adopting emulsion polymerization, an environmentally friendly solution to make available polymers as water-based latex dispersions. The composites containing 5 wt% of polymer, exhibited better elastic behaviour, with up to twice the toughness of the reference sample and of a sample produced with commercial styrene-butadiene rubber latex. Moreover, the additives reduced the apparent porosity, promoted phosphate crystallization, modified the size and shape of crystals, and effectively retarded the reaction, extending working time. The acrylic emulsion developing keto-hydrazide self-crosslinking reaction imparted better properties to the composite, thanks to the synergistic effect with the MPC setting reaction.
17. Foam and rheological behavior of polydentate phosphonate-modified polymers under cement system
Construction and Building Materials,Volume 291, July 2021, 123205
Polymer superplasticizer and residual polyether have a key effect on the quantity and size distribution of air-voids in hardened concrete. In this study, the surface activity and foam properties of polydentate phosphonate-modified polymers RM-1 and RM-2 in aqueous solution were studied. Results revealed that the propylene oxide (PO) units in the polymer structure affected the foaming properties of polymers. The compounding performance of polymers RM-1 and RM-2 with ester-type polycarboxylate superplasticizer (PCE-1) in aqueous solution and cement mortar was also studied. This kind of phosphonate-modified polymers can be used as excellent concrete rheological modifier agents because they generate many small bubbles when compounded with PCE-1. Analysis of the foam properties of polymer RM-1 in aqueous solution and cement pore solution revealed that the calcium ions in cement pore solution are beneficial to stabilize the bubbles produced by the polymer. This study provides a new way to study the properties of phosphonate admixture and its combination with PCE from the perspective of bubble and rheology in aqueous solution and cement mortar.
18. Application of microbial self-healing concrete: Case study
Construction and Building Materials, Volume 291, July 2021, 123226
It has become a green and environmentally friendly method to repair concrete cracks by microbial induced calcium carbonate precipitation (MICP). However, most studies were concentrated in the laboratory, and practical engineering applications are rarely conducted. Hence, in order to promote the application of microbial self-healing concrete, the researches of microbial healing agents and self-healing concrete were carried out. Then, the construction technologies of microbial self-healing concrete were explored through engineering practice. Results showed that the spray-dried fermented bacteria method has great potential for the production of powder-based and capsule-based microbial healing agents of concrete. Compared with the liquid-based healing agents, it was more convenient in terms of production, transportation, storage, and use. For the existing concrete production line, the feeding of microbial healing agents draws on the production experience of fiber concrete. To guarantee the self-healing effects, necessary curing measures should be taken to keep the cracks wet and supply nutrients for bacteria. The degree of self-healing can be evaluated by observing the changes in ultrasonic wave speed and waveform, which is an effective non-destructive method to quantitatively characterize the self-healing efficiency in construction sites. The production and construction experience provided a good reference for the commercialization of microbial self-healing concrete.
19. Coupling effect of steel slag in preparation of calcium-containing geopolymers with spent fluid catalytic cracking (FCC) catalyst
Construction and Building Materials, Volume 291, July 2021, 123194
Spent FCC catalyst coupling with steel slag has been used to synthesize a new calcium-containing geopolymer binding material with excellent performance. The effect of the composition of the raw materials on the performance of the obtained samples has been investigated systematically. The results indicate that the compressive strength of the prepared geopolymers was increased with the addition of steel slag. This is due to the calcium-containing components in the steel slag, which possess higher reactivity compared to the pure chemical reagent in the alkaline activation environment, which is beneficial for the generation of N(C)-A-S-H amorphous gel (where N = Na2O, A = Al2O3, C = CaO, S = SiO2, and H = H2O) in the obtained samples. Meanwhile, the other components of steel slag would embed in the cementitious material as skeleton materials, which are conducive for the improvement of the compressive strength performance. In addition, the role steel slag plays in the geopolymerization reaction has been studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectrometry (FT-IR). Results indicated that the catalyst-derived geopolymer gel (N-A-S-H) coexisted with slag activated gel (C-S-H/C-A-S-H) in the binding matrix, which are the main phases in the geopolymer, and the development of better compressive strength is attributed to the formation of Ca-rich gel phases. These results highlight the feasibility of using spent FCC catalyst and steel slag as raw materials for the production of geopolymer binding material with enhanced compressive strength.
20. Experimental behaviour and numerical modelling of timber-timber composite (TTC) joints
Construction and Building Materials, Volume 291, July 2021, 123273
Push-out tests were conducted on 15 groups of symmetric timber-timber composite (TTC) joints with coach screw shear connectors. The push-out test results were used to characterise load-slip, peak load carrying capacity and failure mode of the composite shear connection between timber slab made of cross laminated timber (CLT) and timber beams/joists made of laminated veneer lumber (LVL) and/or glued laminated timber (GLT). Effect of coach screw size, type of engineered wood product (i.e. LVL-to-CLT and/or GLT-to-CLT), GLT grade, thickness of the CLT slab and orientation of load with respect to the outermost layer of CLT on the structural behaviour of the TTC joints were studied. In addition to the TTC connection tests, embedment strength of the LVL, CLT and GLT and bending yield strength of the screws were experimentally determined and the results were incorporated into a versatile nonlinear beam on inelastic foundation finite element (FE) model to capture the full range load-slip response of the TTC connection. The nonlinear FE models (including material and geometrical nonlinearities) were validated against the test data produced in this study and available in the literature and it was shown that the proposed nonlinear FE model can accurately predict the load-slip, stiffness and peak load carrying capacity of the TTC joints with screw shear connectors. The ultimate strength of the TTC joints were also estimated by modified European yield model (EYM) and comparison of the experimental peak load with EYM and FE predictions demonstrated the significant influence of the rope effect on the full range load-slip response and ultimate load carrying capacity of the TTC joints with dowel shear connectors.