Công bố quốc tế trong lĩnh vực kiến trúc, xây dựng (Tuần 4 tháng 6-2021)
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:
– Xác định các thông số thiết kế hệ thống năng lượng mặt trời thụ động trong các lớp vỏ tòa nhà văn phòng ở vùng khí hậu nóng ẩm bằng kỹ thuật khai phá dữ liệu
– Phương pháp tiếp cận đa lớp định hướng hiệu suất năng lượng trong thiết kế tòa nhà: nghiên cứu điển hình ở Trung Quốc
– Thay đổi mô hình không gian xanh đô thị và nguy cơ nắng nóng ở thành phố Hà Nội trong quá trình thực hiện Quy hoạch tổng thể 2030
– Tối ưu hóa đồng bộ cơ sở hạ tầng xanh và xám để đối phó với những yếu tố không chắc chắn bên ngoài
– Đánh giá sự cân bằng sinh thái giữa cung và cầu của cơ sở hạ tầng xanh lam và xanh lục
Khoa học và công nghệ trong lĩnh vực xây dựng:
– Tác động của quá trình phát triển đô thị đến môi trường nhiệt bề mặt nội đô: bằng chứng từ 323 thành phố của Trung Quốc
– Nghiên cứu về cường độ, độ bền và khả năng chống ăn mòn của bê tông trong môi trường biển.
– Đánh giá các đặc tính cơ học và độ bền của bê tông hiệu quả về mặt sinh thái được sản xuất bằng chất đánh bóng sứ và chất thải scheelite
– Tái chế bê tông thải làm cốt liệu mịn và tro bay làm chất kết dính trong sản xuất bê tông bọt cách nhiệt
Vật liệu xây dựng:
– Mô phỏng bê tông nhựa chính xác và hiệu quả dựa trên các đặc tính tôpô của cốt liệu
– Điều chế và tính chất cơ học của hỗn hợp nhựa đường được gia cố bằng sợi tre biến tính
– Vật liệu sinh học dịch chuyển không đồng nhất, biến dạng và trương nở khi hấp thụ/giải hấp thụ hydric: Tương quan hình ảnh 2D trên gỗ vân sam
– Cải thiện hiệu suất nhiệt độ cao của bê tông geopolymer sử dụng nano-silica, micro-silica và styrene-butadiene latex
– Đặc điểm cấu tạo của tường rơm chịu lực
Xin trân trọng giới thiệu!
QUY HOẠCH ĐÔ THỊ
1. Identification of passive solar design determinants in office building envelopes in hot and humid climates using data mining techniques
Passive solar design is an effective strategy to alleviate the energy-intensive status of the building sector. Identifying passive solar design parameters that significantly impact office buildings’ energy performance can further understand sustainable design principles and prioritize energy efficiency measures. This study proposes a holistic methodology integrating data mining techniques and parametric energy simulation to explore the critical design parameters in passive solar office building envelopes in hot and humid climates. The data mining module incorporates Extreme Gradient Boosting Decision Tree (XGBoost) and association rule mining to measure feature importance and extract strong correlations, respectively. A case study, using a typical office building in Guangzhou, China as a reference building, is conducted to demonstrate the implementation procedure and feasibility of the proposed approach. In total, 115,200 design scenarios are created and simulated in EnergyPlus software. The results of XGBoost show that the glazing system, window-to-wall ratio, and roof coating are the most critical design factors, with importance scores of 0.4858, 0.3197, and 0.1297, respectively. Similarly, based on a confidence threshold of 30% and a lift threshold of 3.0, the extracted association rules indicate that the above three factors have the strongest correlations with the energy consumption level. Findings of this study will provide practical passive solar design guidance for office buildings in hot and humid climates to achieve energy-saving targets. Also, the developed simulation-based data mining method can be applied to other building types in different climates.
2. A target-driven decision-making multi-layered approach for optimal building retrofits via agglomerative hierarchical clustering: A case study in China
The optimization of energy, environmental and economic (3E) outcomes is the principal approach to identifying retrofit solutions for a sustainable built environment. By applying this approach and defining a set energy performance target, this study proposes a makeshift decision framework that integrates a data mining procedure (agglomerative hierarchical clustering (AHC)) into the decision-making process to provide a simplified 3E assessment of building retrofits on a macro-scale. The framework comprises of three model layers: (1) a building stock aggregation model, (2) an individualistic 3E model that provides the sensitivity analysis for (3) a life cycle cost-environmental assessment model. The framework is demonstrated and validated with a case study aimed at achieving the set energy targets for low-rise office buildings (LOB) in Shanghai. The model defines 4 prototypical buildings for the existing LOB blocks, which are used for the individual evaluation of 12 commonly applied retrofit measures. Subsequently, a simplified LCC-environmental assessment was performed to evaluate the 3E prospects of 2048 possible retrofit combinations. The results uniquely identify retrofit solutions to attain the set energy performance targets and optimal building performance. Furthermore, the decision criteria for different investment scenarios are discussed. Overall, this study provides building investors an innovative framework for a facile and holistic assessment of a broader range of retrofit alternatives based on set performance targets.
3. Standardizing thermal contrast among local climate zones at a continental scale: Implications for cool neighborhoods
The Local Climate Zone (LCZ) classification system provides a standardized framework to differentiate neighborhoods for intra-city heat island studies. Yet the thermal contrast of air temperatures over different LCZs has not been examined at a continental scale. Using ground-based meteorological observations in 2016, here we investigated the seasonal thermal behaviors of various LCZs over China. Measured air temperatures over studied LCZs are found to have strong relations with latitude, altitude, and the distance to coastline. Thermal contrasts reduce to less than 1 °C in all seasons after removing the signal of background mean air temperature determined by geographical conditions. Despite the air temperature variation within individual LCZs, results reveal consistent characteristic air temperature regimes of LCZs exist at a continental scale. The warmth of built type LCZs is more evident at night, with an annual mean air temperature difference of 0.51 °C compared to the low plant LCZ. Among the studied LCZs, compact mid-rise neighborhoods have consistently high air temperatures throughout the year. Comparative analysis suggests that open high-rise neighborhoods are preferred over compact mid-rise and low-rise neighborhoods for sustainable city development. Our results provide useful guidance for landscape design and planning to create cool cities and neighborhoods.
4. Multi-performance based computational model for the cuboid open traveling salesman problem in a smart floating city
The term “smart city” has been emerged as a novel solution to uphold the useless urban areas and the term has taken the advantage of sustainable and environmental resources. On the other hand, the term “floating city” has been studied for just only a few years as alternative living spaces for humanity across the world since land scarcity has already begun. Therefore, in this research, we propose multi-objective optimization algorithms to obtain the Pareto front solutions for the cuboid open traveling salesman problem (COTSP) in a “smart floating city” context. Given n nodes and the distances between each pair of nodes, the COTSP in this paper aims to find the shortest possible tour with a traveling distance that starts from the depot (i.e., node 1) and visits each node exactly once without needing to return to the depot. As known, a cuboid has height, length, and depth and the COTSP defines its x, y, z coordinates as a cuboid corresponding to height, length, and depth. In addition to the traveling distance, the platform (building breakwaters) cost is measured by the z coordinates (depths) of the nodes/platforms that represent both the platforms below the sea level. Note that unlike the traditional TSP, it has a variable seed number and a variable number of nodes/platforms in each solution. The paper aims to find the Pareto front solutions by minimizing the traveling distance and platform cost of the infrastructures below the sea level simultaneously. We develop a multi-objective self-adaptive differential evolution (MOJDE) algorithm, a nondominated sorting genetic algorithm (NSGAII), and a harmony search (MOHS) algorithm to solve the problem in such a way that we minimize the traveling distance while minimizing the platform cost simultaneously. All algorithms are compared to each other. The computational results show that the MOJDE and NSGAII algorithms outperform the MOHS algorithm in terms of commonly used performance measures from the literature.
5. Understanding land surface temperature impact factors based on local climate zones
The local climate zone (LCZ) and land surface temperature (LST) have gained considerable attention as urbanization continues to increase. However, the study of LSTs lacks a regional complexity perspective. In order to explore the law of urban thermal environment, impact factors of LSTs are identified using GIS spatial analysis and statistical analysis methods in conjunction with parameter models that reflect urban spatial morphologies on the LCZ scale. The research results show that the LST ranges from 24.90 °C (LCZA) to 33.26 °C (LCZ2) in the summer of 2017 and from 2.53 °C (LCZ7) to 2.89 °C (LCZ3) in winter; LST ranged from 22.00 °C (LCZ2) to 28.19 °C (LCZE) in summer 2019, and from -4.79 °C (LCZ10) to -2.12 °C (LCZ3) in winter. Different LCZs had different impacts on LSTs. LST is always positively correlated with the floor area ratio, with a maximum correlation coefficient of 0.682 in LCZ2. It exhibits the highest positive correlation (correlation coefficient = 0.421) with average building height in LCZ3 and the highest negative correlation (correlation coefficient = -0.706) in LCZ7; vegetation and water bodies have a cooling effect. These results can serve as a valuable reference for building cool communities and improving the living environment of residents.
6. Cities are going uphill: Slope gradient analysis of urban expansion and its driving factors in China
Rapid urbanisation causes large urban conversions of natural and agricultural land to non-agricultural use. Research on urban expansion has typically disregarded gradient characteristics. The current study uses slope data calculated based on the Shuttle Radar Topography Mission Digital Elevation Model data set and multi-period land cover data derived from China’s Multi-Period Land Use Land Cover Remote Sensing Monitoring data set to reveal the evolution of spatiotemporal patterns of vertical urban expansion in China from 1990 to 2015. A built-up land climbing index is specifically defined to measure the increasing use of land with slopes. A slope-climbing phenomenon has become increasingly apparent over time. Although built-up land with slopes below 5° accounts for over 85% of the total, this proportion has declined steadily from 89.53% in 1990 to 86.61% in 2015. The number of cities where built-up land was developed on high slopes (over 5°) increased from 150 to 238. Slope-climbing intensity spatially increased from north to south, and showed a “low–high–low” pattern from west to east. In addition, built-up land showed evident slope-climbing trend in areas with high variation in slope. Slope-climbing intensity was high for cities located in mountains and ethnic autonomous prefectures. Lastly, cities going uphill are subjected to the combined effects of natural environmental conditions and social factors. The average slope and population growth have significantly positive impact on slope-climbing intensity.
7. Altering urban greenspace patterns and heat stress risk in Hanoi city during Master Plan 2030 implementation
Hanoi City has been greatly reshaped owing to its “Master Plan by 2030 and a vision to 2050 by Decision 1259/QD-TTg of Vietnam” (called Hanoi Master Plan thereafter). This Hanoi Master Plan results in multi-challenges for the Hanoi City in terms of conserving urban greenspace (UGS). This study pursues to (1) investigate the changing environmental spatial patterns of UGS, (2) identity the areas at high risk due to heat stress based on abnormal land surface temperature (LST) distribution and demographic vulnerability, and (3) suggest mitigation strategies to the authorities by using the proposed UGS management platform. Sentinel-2 multispectral instrument (MSI) data was used to examine the evolution of UGS in relation to LST derived from Landsat 8 OLI thermal band that was subsequently utilized to create heat stress risk patterns. The study region is the inner Hanoi City. The UGS was investigated during the timeframe from Oct. 2016 to Oct. 2018. Accuracy assessment was performed by using Google Earth and field survey data. Results showed that UGS in inner Hanoi City is much declined by 1.3% for woodland and by 4.4% for shrub land, while grass-cover is increased by 2.4% in recent 2 years. Overall accuracies are of 96% and 88% with Kappa coefficients of 0.92 and 0.78 for land cover classification in 2018 and 2016, respectively. Urban heat stress index patterns showed a higher risk in the central inner-city areas of dense residential regions characterized by dense built-up. The identification of environmental heat stress risk patterns provides useful information for calling more attention of urban planners, authorities and health organizations.
8. Multi-objective optimization for green-grey infrastructures in response to external uncertainties
The optimized green-grey infrastructures are promising solutions to combat the urban flood and water quality problems which have been severe owe to the increasing urbanization and climate change. However, the focusses in existing researches have been either on finding the best strategy by scenario analysis method or optimal design of LID practices under the hypothesis of unchanged grey infrastructures. Little is known regarding the synergistic effect of synchronous optimization design of both green and grey infrastructures. In the study, we conduct green-grey infrastructures synchronous optimization by modifying the decision variables of traditional simulation-optimization frameworks and investigate how external uncertainties will affect their performance. The methodology was applied to a case study in Suzhou, China. The results showed that although the cost of green-grey synchronous optimized scenarios is lower than that of green optimized only scenarios by 1.69–4.19 thousand USD per km2, the runoff/pollutants reductions of green-grey synchronous optimized scenarios are 0.11%–5.24% higher than that of green optimized only scenarios. In the green-grey synchronous optimized scenarios, green infrastructures can contribute to runoff/pollutants control by 50%–63%/62%–70%, while grey infrastructures can contribute to the remaining part by 37%–50%/30%–38%.
9. Assessing the ecological balance between supply and demand of blue-green infrastructure
Given that improving urban ecological environment requires a clear recognition of the urban ecological elements, investigating the ecosystem service capabilities of urban green-blue infrastructures (UGBIs) becomes ever important. This study aims to reveal and compare the synergistic ecosystem service ability of UGBIs with different characteristics and the relationship with human demand in Wuhan city. It was found that the climate regulation service and water regulation service value of lake-type parks both reached the highest over the other UGBIs. Nature-type parks revealed the most capable cultural service, and green-type parks demonstrated the greatest exercise cultural service value. The analysis showed that the ecosystem services delivered by the UGBIs were influenced by the park area, the total value of the normalized difference vegetation index and normalized water body index, and the distance from the city centre. Furthermore, a significant spatial phenomenon was found that the ecological capacity of lake-type parks in the city centre was higher than that of the other UGBIs at the same location. Regarding the relationship with the human activity intensity, the high-demand and high-supply regions were mainly concentrated in highly developed areas in terms of regulating services. Nevertheless, a severe environmental inequality occurred in small urban centres, which requires urgent attention from the government. This work answered the question of where and how to optimize the green-blue infrastructures in Wuhan, and it contributes to the construction of the existing blue-green space.
10. The influence of companion factors on soundscape evaluations in urban public spaces
‘Soundscape’ refers to how individuals or groups of people perceive sounds. This study focuses on whether and to what extent companion factors, compared with other demographic factors, influence the various aspects of soundscape evaluation. Two kinds of companion factors are studied here: one is companion status, the other is the social relationship intensity between companions. Based on a questionnaire and statistical analysis, both companion factors are found to influence evaluations of socially interactive sounds- sound made by human activity. People accompanied are more likely to notice speaking and children sound and prefer safe and social sounds. People involved in closer social relationships tend to notice children’s sounds more and prefer human sound types and social sound. Other factors may offset the influence of companion factors, however. Site factors interfere with accompanied people’s tendencies to prefer safe sounds and notice children’s sounds, and participants’ ages interfere with their tendencies to notice speaking sound. The results of this study suggest that human activity sounds can contribute to social sound among companions, whereas solo people may prefer more privacy and quietness. This study emphasizes companion factors in soundscape evaluations and suggests future soundscape design to satisfy people with different companions.
11. Critical challenges in implementing sustainable transport policy in Stockholm and Gothenburg
This paper explores the mental-models of Swedish planners in order to understand the extent to which they support the ideals of sustainable transport. Focussing on three critical challenges: forecast-led versus vision-led planning; tackling congestion; and, public acceptability; the findings, drawn from in-depth interviews, demonstrate mostly advanced thinking. However, implementation can be at odds with these mental models, highlighting important lessons for other cities. There is a disconnect between the objectives of reducing car use and the continuation of investments in increasing road capacity, and a difficulty in transitioning from forecast-led planning to back-casting. Political controversies and public acceptability for measures to decrease car use are an added challenge.
12. Indoor water end-use pattern and its prospective determinants in the twin cities of Gujarat, India: Enabling targeted urban water management strategies
Water end-use studies disaggregate the quantity and frequency of water uses for various household purposes. Water end-use studies are available but none for India, which is gradually approaching a water-scarce condition from being a water-stressed country at present. This implies a need for incorporating water end-use understanding for augmenting urban recycling plans and strategies. To identify socio-demographic determinants of water end-use consumption for use in targeted urban water management, we focused on the indoor micro-components of bathing, dish-washing, laundering, and cleaning at households across the twin cities of Gujarat, a water-scarce province of India. A mixed-method approach was used for data collection in which questionnaire surveys (estimated or indirect measurements) were coupled with water meters (direct measurements) at households. The twin cities of Gujrat represent a spatial variation in greywater production at homes even at a distance of 30–40 km. Direct measurement showed less total average water consumption in Ahmedabad (83 L/HH/d) than Gandhinagar (105 L/HH/d), while indirect measurement showed indoor average consumption of 427 and 497 L/HH/d in the respective cities. Statistical significance of income, family size, and education was noticed on the water consumption pattern of a household. Besides, the study provides the attitude and practice of users towards water conservation behavior. We present new insights and recommendations for future urban water sustainability that are specific to India and applicable to several south-Asian countries.
13. Roads, railways, and power lines: Are they crucial for bees in urban woodlands?
The loss and transformation of habitats due to human impact are commonly regarded as major factors decreasing the diversity of pollinators. However, there is also some evidence that industrial infrastructure can play a positive role in shaping the composition of many animal communities. Still, little is known about how artificial linear structures, such as roads, railways, and electric power lines, affect the abundance and diversity of wild bees in urban ecosystems. Thus, we attempted to verify which of the habitats mentioned above is crucial for the occurrence of bee species of various functional groups. We conducted field research in woodlands of the city of Bydgoszcz (northern Poland). Site conditions were evaluated on the basis of phytoindicators (plant indicator species). In the study area, we recorded 32 % of all bee species reported from Poland. In respect of species richness and abundance, the habitats along railway lines were the most attractive to bees. Besides, in respect to bee species richness, these sites were the most similar to roadsides. The habitats located under power lines were the poorest in species. About 20 % of bee species were recorded only along railways and 3 % only along roads, while no bee species was recorded exclusively under power lines. Bee species richness and abundance increased with growing cover of the sites by bee food plants and an increasing proportion of bare soil. Moreover, bee abundance increased with an increasing share of plant indicator species of very dry or dry soils and of alkaline soils. Bee abundance declined with an increasing share of plant indicator species of sandy soils. The presented results indicate that roads, railway lines, and power lines, in structurally simplified and floristically poor pine forests, are important for wild bees in urban ecosystems.
14. Predicting citizens’ participatory behavior in urban green space governance: Application of the extended theory of planned behavior
The governance of urban green spaces (UGS) often involves a wide range of stakeholders, each with their own views, preferences, and needs. However, the traditional top-down governance of UGS has struggled to meet the needs of today’s public. By reflecting the different needs of different social groups, public participation has become one of the innovative solutions used to solve the problems of public governance, which has been a widespread concern. Based on the theory of planned behavior (TPB), this study complements environmental responsibility (ER), environmental concern (EC), subjective environmental knowledge (SEK) and media influence (MI) as the factors influencing the formation of citizens’ participatory attitude, and provides multiple influencing paths for increasing citizens’ participatory intention and behavior. A structural equation model (SEM) was used to test the hypotheses of the newly constructed theoretical model based on 1191 questionnaires administered face-to-face in Beijing. The results demonstrate that perceived behavioral control has the greatest positive influence on citizens’ intentions and behaviors; that is, their intention and behavior to participate is strongly restricted by the objective conditions of the citizens themselves. Among the additional impact factors, expected personal gratification (EPG) also has a positive effect on intention. Local governments can increase citizens’ intentions and behaviors to participate in UGS governance through two measures: one is to optimize the process of citizens’ participation in UGS governance to reduce the threshold of participation; the other is to enhance the city’s infrastructure and cultural and entertainment activities to enhance citizens’ environmental responsibility.
15. A parametric model of residential built form for forecasting the viability of sustainable technologies
Renewable supply systems, such as rainwater harvesting and ground source heat pumps, have the potential to improve the sustainability and resilience of residential areas. However, their feasibility partly depends on the dimensions and plot areas of the dwellings, and there has been a lack of a suitable method of modelling these for future urban development. This paper therefore calibrates and validates a method of modelling how the plot areas and footprints of dwellings would vary in size. Its inputs are the total dwellings and their average density for each area type within a district. It could thereby complete a chain of urban modelling from regional to local scale for testing spatial planning scenarios. The results show that the calibration of the model is transferable between spatial scales and UK regions, and the results are validated against detailed GIS data. It is then developed into a novel parametric model to estimate how built form will affect the future potential of renewable supply systems, and this is demonstrated using rainwater harvesting as an example. It provides estimates of water-savings at district scale that are more reliable than the usual method of using discrete average dimensions per dwelling type.
16. Traits of a bloom: a nationwide survey of U.S. urban tree planting initiatives (TPIs)
Municipal leaders worldwide are showing substantial interest in urban greening. This encompasses incentives, policies, and programs to vegetate urban landscapes, and it often includes urban tree planting initiatives (TPIs). Over the past decade there has been a seven-fold increase in scholarly use of terms denoting TPIs, and roughly two-thirds of associated studies address TPIs in the United States (U.S.). This reflects a bloom of scholarly interest in TPIs. Yet, there has been limited research on contemporary TPIs as historically situated cultural phenomena, and there has to the best of our knowledge been no nationwide survey of TPIs across municipal scales. Addressing these gaps, this article presents findings from a survey of 41 TPIs in the United States. We report on typical traits of U.S. TPIs across six themes: background, dates and goals, public awareness, funding and governance, planting, and stewardship. Respondents identified over 115 traits that distinguish TPIs from typical urban tree planting activity, suggesting that TPIs are a discrete form of urban forestry. Over two-thirds of TPIs are funded separate from traditional urban forestry, and lack of institutionalization raises questions about long-term viability. TPIs mobilize political and financial resources for program launch, tree purchasing, and planting, but there may be a need for greater investment in stewardship activities and the social infrastructure that undergirds green infrastructure. Large shade trees for ecosystem services and native trees are the principal factors informing TPI species lists. Beautification and regulating ecosystem functions are, in turn, the principal potential benefits animating tree planting goals, yet few TPIs have conducted research to assess the fulfillment of associated outcomes. This study provides a foundation for future interdisciplinary scholarship on TPIs across the humanities, natural sciences, and social sciences.
17. Geospatial simulation of urban neighbourhood densification potentials
Sustainable Cities and Society, Available online 2 June 2021, 103068
Although densification of urban areas is being proposed as a sustainable urbanisation strategy, frameworks for detailed large-scale analysis of densification potentials and their evaluation are lacking. A geospatial simulation framework is presented to assess and evaluate densification potentials at the neighbourhood level of already built-up residential areas. The focus is on post-war neighbourhoods, which are particularly promising for sustainable densification. Neighbourhoods are localised using geospatial analysis and based on literature and architectural designs, potentials are estimated for different neighbourhood archetypes and densification strategies. Potentials are simulated at a national scale using supervised archetype classification. The embeddedness into current mobility infrastructure is used as a proxy for evaluating the sustainability of neighbourhood densification. The developed framework is tested for Switzerland. Depending on the densification strategy, the simulated additional inhabitants for populating post-war urban neighbourhoods range between 4–14% of the current population. More than half of this potential is located in central areas and is well connected by public transportation. The presented approach is suitable for assessing spatially explicit densification potential and for prioritising densification locations. We show that in countries with a high number of post-war neighbourhoods in well-connected locations, considerable densification opportunities could be realised in already built-up residential areas.
18. Life cycle assessment and life cycle costing of multistorey building: Attributional and consequential perspectives
Buildings are accountable for much of the resource consumption and CO2 emissions generated from human activities. Nonetheless, the focus of building life cycle assessment (LCA) studies to evaluate the environmental footprint are more commonly adopted in an attributional approach. Nevertheless, understanding a direct and indirect consequences in larger system using consequential approach is also needed for policy-making. Rather small body of existing literature has been found on the implementation of consequential LCA and life cycle costing (LCC) in the building sector. In this study, attributional and consequential approach are performed for hybrid wood multistorey building. The results showed that with attributional approach, the phase that contributed the environmental impacts the most in climate change category is the production phase yet it became the use phase if consequential approach is used. By performing consequential LCA-LCC the possible hidden impacts can be uncovered and sufficient insights into the indirect impacts can be seen, thereby offering stakeholders the opportunity to avoid such future consequences.
19. Policy analysis for high-speed rail in China: Evolution, evaluation, and expectation
The success of HSR development can be attributed to strong policy support from the Chinese government, whose policies have various effects on HSR development due to several complex factors. This paper investigates HSR policies launched by the Chinese government based on policy text analysis. To put forward proposals for the development of HSR in China, we trace the evolution of HSR policies, compare the policy tools, and identify the prospects for HSR policy. The main results are as follows: (1) The progress of HSR development in China can be grouped into five major phases: preliminary planning, technology improvement, large-scale construction, stagnation, and going global; (2) based on our policy keywords analysis, we identify the core policy themes of HSR, which include technology development, financial support, engineering projects, and safety system; (3) regulatory policy tools are most often used, followed by information tools and economic tools. Furthermore, we investigate different types of policy tools that can be used in the four HSR policy themes; and (4) this paper proposes that future HSR policy should coordinate with other policies to construct a modern transport system, use integrated policy tools, stimulate demand-side policy, and build a policy system supporting global development.
20. Comparative assessments and insights of data openness of 50 smart cities in air quality aspects
Data Openness is considered as an indispensable component for scientific innovation, community engagement and smart city development. In this study, a Data Openness in Air Quality (DOAQ) framework that consists of 3 tiers with a total of 23 open data principles was established to assess and monitor the status and development of data sharing, release and centralization of air quality information in the top 50 smart cities (Top50SC) around the world. The DOAQ utilizes additive formulas with predefined coefficients to obtain scores in each tier, thus reflecting the relative importance on data availability and visibility of different air quality data. The scores of DOAQ were compared with the smart cities scorings from Eden Strategy Institute and ONG&ONG Pte Ltd. (2018), and other socioeconomic attributes (i.e., social, political and humane) within the current study. Strong correlations (i.e., 0.4−0.6) among these indices implicate that the status of air quality reporting could be a good proxy to gauge the environmental data openness in a city. Lastly, good practices (e.g., apps and air quality forecasts), essential criteria and directions for future smart city development on air quality reporting were summarized, with the aim of laying down practical and efficient guidelines for individual smart city that desires to seek for improvements in air quality data openness.
21. Co-designing vacant lots using interactive 3D visualizations – Development and application of the Land.Info DSS
Collaborative processes of co-production between end-users and designers can be an effective means to produce shared understanding about a system and has been shown to improve the quality of, and support for, design outcomes. In spatial design and planning, co-production usually involves engaging community members in the design and planning of their local environment (co-design). However, to support co-design of landscapes it has been recommended that decision support systems (DSS) be developed for both the specific decision setting, and in conjunction with meaningful public guidance and input, to transition professional practice to working with rather than for the public. The research presented here responds to these recommendations by developing and evaluating a process for involving end user residents in the co-production and application of the Land.Info DSS in the design of multifunctional landscapes within their communities. The research used participatory workshops incorporating a structured elicitation process, agile software development, and user evaluation to design and test a video game-based DSS in context of two real-world design settings in Detroit, MI, USA. In this paper, we describe and evaluate the process and outcomes, with the results showing improved evaluation over the course of development and overall positive outcomes from this type of collaboration. We also found that residents required additional information to orient themselves in the DSS. In addition, visualization realism and ease of use of the DSS contributing to dialogue during co-design sessions. The paper ends with recommendations for future development and research.
KHOA HỌC VÀ CÔNG NGHỆ TRONG LĨNH VỰC XÂY DỰNG
1. Impacts of the evolving urban development on intra-urban surface thermal environment: Evidence from 323 Chinese cities
Urban development has significantly modified the surface thermal environment in urban areas. This study provides the first attempt to characterize the urban development imprint on surface thermal environment for 323 cities across the entire country of China, using an intra-urban perspective. Specifically, it investigates the variation of surface thermal environment in terms of land surface temperature (LST) difference triggered by significant urban evolution of intra-urban division containing two primary classes: old urban areas developed by 1992 and new ones expanded in the 1992–2015 period. Under this “old-new” dichotomy, the relationship between urban development and the LST difference is explored through Multi-scale Geographically Weighted Regression (MGWR). Results reveal that urban development is closely related to the difference in LST between old and new urban areas in 2015, which varies from −2.66 °C to 2.46 °C, up to -6.27 °C in western China. 264 cities manifest relatively “cooler” urban environments in the generally larger-sized new urban areas. The seven selected urban development indicators can explain 75% of the variance in the LST difference through MGWR. Among them, the old-new elevation difference, the normalized difference vegetation index (NDVI) difference, and Gini coefficient are found to influence the LST difference in various spatially varying manners. The elevation difference, a generally underestimated nature-driven indicator, is found dominant in explaining the LST difference for 252 cities, among which 216 cities demonstrate higher LSTs in the urban areas with lower elevations. Overall, this study provides valuable information of human-environment interaction across many cities in a generalized way, which complements similar studies at local level, and helps to depict a complete picture of environmental impacts of urban development. The integrated workflow can also be promoted to other periods or other countries to examine the corresponding urbanization imprint on intra-urban surface warming.
2. A step-by-step numerical method for optimization of mechanical ventilation in deep underground enclosed parking lots: A case-design study
Journal of Building Engineering, Available online 4 June 2021, 102799
To reduce polluted air, mechanical ventilation (MV) is essential for enclosed parking spaces. The traditional prescriptive design method, the index-based design, cannot guarantee ventilation performance of each fan in the enclosed parking lot. To solve this, the performance-based design approach is the best alternative that specifically addresses performance-related criteria of MV system. In this study of practice-based learning in a real construction project, we proposed a unique design optimization methodology for improving the performance of MV systems using iterative, step-by-step computational fluid dynamics (CFD) simulation. Five numerical simulation levels on seven engineering steps and a techno-economic analysis were utilized. Ultimately, fan selection was based on calculating the airflow and pressure requirements of a MV system and finding a fan of the right design to hedge against the risk of system effect and surging phenomenon. Results showed that a stable fan selection with an error of 5% of the design air flow rate could be implemented by repeating numerical analysis for the performance optimization of the MV system. When the MV design optimization was applied to the reference parking lot, the number of fans could be reduced by 30%, and energy demand of the MV system by at least 16%. Consequently, the annual energy savings was projected to recover the increase in initial investment cost in about 5.8 years. The key contribution of this research is that it overcame the limitations of the traditional index-based design for selecting the optimal fans of MV systems.
3. Experimental Characterization of Quaternary Blended Mortar Exposed to Marine Environment using Mechanical Strength, Corrosion Resistance and Chemical Composition
Journal of Building Engineering, Available online 4 June 2021, 102822
The durability of concrete is significantly influenced by its binder composition, especially in the presence of aggressive chemical environment. This paper represents a study on the strength, durability, and corrosion resistance of quaternary blended mortar made with Portland pozzolana cement (PPC), ground granulated blast furnace slag (GGBS) and rice husk ash (RHA) exposed to marine environment. Binary blended concrete mix using GGBS and RHA as partial replacement for cement is already well established. Previous research reports several shortcomings in using binary blended and ternary mix including low initial strength and increasing shrinkage strains with increasing percentages of GGBS, silica fume and RHA as partial substitutes for cement. Hence, this study is focused on overcoming the limitations of binary and ternary blended mixes by implementing a quaternary blended mix using GGBS and RHA to partially replace cement. This quaternary blended cementitious system is optimized based on its mortar compressive strength, determined by varying the percentages of GGBS and RHA as substitute for cement. These optimized quaternary mortar specimens are moist-cured for 28 days and then exposed to an artificially prepared marine environment for 180 days. The optimized quaternary blended mortar specimens show improved mechanical strengths, both compressive and flexural. These specimens also exhibit enhanced resistance to chloride penetration, corrosion, and water absorption compared to the control mix after 28 days of water curing. A quaternary blended mortar mix prepared with 70% PPC, 20% GGBS, and 10% RHA exhibits the maximum mechanical strength, resistance to chloride penetration, and corrosion, mass loss and water absorption upon exposure to marine environment up to a period of 180 days. Mineralogical analyses using X-ray diffraction (XRD), chemical bond analyses using Fourier Transform Infra-Red (FTIR) spectroscopy, and microanalyses using scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray spectroscopy (EDS) are implemented to determine the effects of marine environment exposure on the different mixes. The findings are then used to corroborate the observations from the specimen scale mechanical and chemical characterizations.
4. Evaluation of the mechanical and durability properties of eco-efficient concretes produced with porcelain polishing and scheelite wastes
The construction industry uses large-scale natural resources to production of concrete among which cement and aggregates are fundamental components. This process causes environmental impacts that are not aligned with sustainable propositions and perspectives. Likewise ceramic and mining industries generate various wastes disposed of inappropriately which can be harmful to environmental systems. Given these facts the present study aims to understand better the physical mechanical and durability of eco-efficient concrete produced with partial and hybrid substitutions of cement and sand by porcelain polishing residue (PPW) and scheelite residue (SW) respectively. For this an experimental campaign was developed divided into two stages. The first phase consisted of performing tests (consistency water absorption and porosity by immersion and compressive strength) in concretes with fixed fine aggregate contents (mixture of 81% and 19% of SW and sand respectively) and with partial replacement of Portland cement by 0 5 10 15 20 25 and 30% of PPW aiming to select the mixture with better physical and mechanical performance. Finally the second experimental phase consisted of evaluating the evolution of compressive strength and durability (capillary water absorption and chloride penetration) properties of the selected eco-efficient concrete. A microstructural analysis using XRD was also conducted to identify the main phases present in the concretes with wastes. The results showed that 15% is the optimum content to replace cement with PPW. A decrease in the consistency compressive strength water absorption and porosity of the concretes with this waste compared to the reference mixture was also observed 28 days. However at 90 days the mechanical behavior of the concretes was improved due to the filling effect and the pozzolanic activity of PPW. The durability properties indicated less pore connectivity and resistance to chloride migration equivalent or slightly higher than the reference concrete.
5. Green city and regional environmental economic evaluation based on entropy method and GIS
Environmental Technology & Innovation, Available online 2 June 2021, 101667
In today’s society, the environment is a frontier topic, and the topic of environmental sustainability has attracted attention. There are also many sustainable development ideas in the economic field. The main topic is circular economy, which is mainly to cultivate a harmonious coexistence environment for the development of man and nature by strengthening the construction of the ecological environment and ecological industries. Therefore, when solving environmental problems, we must adapt measures to local conditions and develop a circular economy to fundamentally solve the problems that have always existed between resources, environment and development. For regional economies, we must create new ideas on the road to industrialization and make full use of Resources provide a foundation for the realization of the overall construction goals of a well-off society in the near future, and contribute to the realization of grand goals. In this study, we will take the environmental problems in a certain area as an example, aiming at the environmental problems in the area and the goals of national policies for ecological environment construction, summarizing the content of existing research, and conducting a preliminary analysis of this content. A framework of thinking based on ecological environment quality evaluation is proposed. Technically, remote sensing and geographic information systems are used, and the survey results and research results summarized with sufficient reasons are used to conduct a single-factor analysis of the ecological environment in the area, and establish a relevant database of the ecological environment in the area. The focus of this article is to establish a complete set of evaluation system compared with the current situation and development of circular economy, and compared with foreign circular economy development models. The main contents include the evaluation of the reduction of resource input, the evaluation of the effect of resource recovery and reuse, the evaluation of the reduction of pollution emissions, the evaluation of the improvement of ecological environment quality, and the evaluation of the comprehensive development level of the socio-economic development of the area. On the basis of some evaluations, it is necessary to use the entropy method to make a comprehensive analysis and evaluation of regional economic development. The evaluation system of this article is relatively complete and comprehensive, integrating resources, environment and economic benefits.
6. Wood I-joists with web holes and flange notches: A literature review
Wood I-joists are increasing being used as floor and roof joists in the construction of commercial and residential buildings, due to their light weight, high strength, easy handing, and good durability. Web holes and flanges notch are often made in the joists to allow passage of ventilation systems, electrical wiring, and service pipes, but it is strictly restricted by joist manufactures. If not handled improperly, it is very easy to produce the crack growth and eventually result in catastrophic damage. This paper presents a comprehensive review on experimental studies investigating the mechanical performance of wood I-joists web holes and flange notches. The effect of flange-notches and web-holes on the structural performance (e.g., ultimate load carrying capacity, shear strength and stiffness) of unreinforced I-joists are discussed and typical failure modes are described. Reinforcement techniques may be required to improve the mechanical behavior of deficient joists, and the existing design approaches are presented. Based on the findings from this review, recommendations are proposed for future works, which can provide a reference for further research on wood I-joists.
7. Principal component analysis approach to dispersed graphene oxide decorated with sodium dodecyl sulfate cement pastes
Although researchers have investigated the properties of nanomaterials in cement paste, the relationship between cement paste properties and dispersion properties is not yet understood. Understanding dispersion properties may reveal how nanomaterials changes cement paste properties. In this study, Taguchi-based principal component analysis (PCA) was used to uncover the mechanism of interaction between dispersion and cement paste properties. Using graphene oxide (GO) with smaller particles, higher zeta potential of dispersion, and higher sodium dodecyl sulfate levels led to greater splitting tensile strength, ultrasonic pulse velocity, and hydration rate and lower thermal conductivity, electrical resistance, porosity, and percentage of water absorption. Optimum sodium dodecyl sulfate usage significantly improves the mechanical properties and degree of hydration due to hydrophobic association. A significant improvement in thermal conductivity, calcium hydroxide content, and porosities of 21.33%, 13.88%, and 10.21% was achieved in the cement pastes using a 0.1% GO and a 0.1% sodium dodecyl sulfate by weight instead of cement. The dispersion properties significantly affect the properties of cement pastes, which accounts for 97% of product variability.
8. Impact resistance of steel fiber-reinforced self-compacting concrete (SCC) at high strain rates
The frequent or occasional impact loads pose serious threats to the service safety of conventional concrete structures. In this study, the impact-related properties of self-compacting concrete (SCC) with 0.5%, 0.75% and 1.0% steel fibers are systematically investigated with a Split Hopkinson Pressure bar (SHPB). Results show that the steel fibers with content no more than 1.0% can be successfully used to prepare SCC with good workability and greatly improved impact resistance. The impact properties including failure modes, peak stress, peak strain and elastic modulus are all significantly influenced by strain rate and steel fibers content. There exists a linear relationship between the dynamic increase factor (DIF) of steel fiber-reinforced SCC and the decimal logarithm of strain rate. Steel fiber-reinforced SCC generally presents higher DIF than that of steel fiber-reinforced normal concrete, showing a more remarkable strain rate effect. The impact toughness index (ITi) is defined to assess the impact resistance of steel fiber-reinforced SCC. The addition of steel fibers considerably increases the ITi of SCC, implying highly improved impact resistance. When 1.0% steel fibers are included, the average ITi of SCC is increased by 18.8%.
9. Behaviour of rectangular RACFST slender columns under eccentric compression
Experimental and numerical studies on the static behaviour of eccentrically compressed recycled aggregate concrete filled steel tube (RACFST) slender columns with rectangular cross-section are reported in this paper. Fifteen specimens were tested under eccentric compression. The factors considered in the experimental investigation included: 1) depth-to-width ratio (β), from 1.0 to 2.0; 2) load eccentricity ratio (m), from 0 to 0.6; 3) slenderness ratio (λ), from 20 to 40; and 4) recycled coarse aggregate (RCA) replacement ratio (r), from 0 to 100%. The experimental results show that failure of the eccentrically compressed specimens is manifested with major local buckling of the steel tube coving compression flange and part of side walls near the mid-height section and the crushing of the concrete core at the same location. The eccentrically compressed specimens generally possess stable load versus deformation curves including the initial linear and the subsequent nonlinear stages before reaching the peak load and the post-peak descending stage. In addition, when other parameters keep constant, the specimens with larger m, λ and r possess smaller bearing capacity (Nue), and m has more significant effect on Nue than λ and r. Numerical simulation of the eccentrically compressed rectangular RACFST slender columns is also carried out by a finite element analysis (FEA) model built in ABAQUS, and the model is verified by experimental results. The typical mechanism of rectangular RACFST slender columns under eccentric compression is further revealed by the FEA model. Finally, simplified formulae for the bearing capacity are developed, and the comparison between simplified and experimental results indicates that the simplified model is accurate in predicting the bearing capacity of rectangular RACFST slender columns.
10. Review of dynamic behaviour of rubberised concrete at material and member levels
The reuse of waste tyres satisfies the requirements of sustainable development. Many researchers mix concrete with recycled rubber particles obtained from waste tyres to produce rubberised concrete, which exhibits improved mechanical properties. Although numerous studies have been performed on the mechanical behaviour of rubberised concrete, most of these were focused on its static behaviour, which is the shortage for rubberised concrete research. The achievement of dynamic behaviour of rubberised concrete is limited. It has been demonstrated that the addition of rubber particles can improve the fatigue performance, seismic performance, impact resistance, and explosion resistance of concrete. Therefore, it is necessary to summarise the dynamic behaviour of rubberised concrete materials and members to further civil engineering practitioners’ understanding of rubberised concrete and thereby, promote its application and development. This paper systematically summarises the mechanical properties of rubberised concrete under fatigue loads, earthquake loads, impact loads, and explosion loads from the material level to the member level. It also proposes a feasible direction for future research on rubberised concrete under dynamic loads.
11. Applicability of random decrement technique in extracting aerodynamic damping of crosswind-excited tall buildings
At the vicinity of vortex lock-in wind speed, the nonlinear aerodynamic damping effect is significant. It can greatly promote the surge of crosswind response, even threaten structural safety and serviceability of tall buildings. Techniques dependent on experimental measurement to identify aerodynamic damping have been developed for estimating crosswind response from wind loading spectrum. Random decrement technique (RDT) as one frequently mentioned technique of system identification has been used in literature to extract aerodynamic damping from stochastic crosswind response, although it was originally suitable for linear single degree of freedom system with a constant damping ratio. This study investigates the applicability of RDT in extracting aerodynamic damping of tall buildings. The models of linear and nonlinear aerodynamic damping are applied to simulate crosswind response of a square section tall building. Accordingly, the wind loading spectra based on high-frequency-force-balance (HFFB) testing and the model recommended by AIJ are utilized respectively to consider the effect of random wind load on the characteristics of crosswind response. To examine the accuracy and efficiency of RDT, aerodynamic damping is extracted through two approaches and compared with target value. Moreover, the influence of varying wind loading spectra on amplitude-dependent aerodynamic damping is demonstrated.
12. Recycling waste concretes as fine aggregate and fly ash as binder in production of thermal insulating foam concretes
This paper presents the first investigation on foam concretes with fly ash and fine recycled concrete aggregate (RFA). Foam concretes were produced considering 0, 25, 50, 75 and 100% RFA ratio instead of virgin sand. Tests were conducted to assess their porosity, density, compressive strength, dynamic elastic modulus, absorption, ultrasound and thermal characteristics. Scanning electron microscopy analyzes were performed for investigating the microstructure of concretes. Findings show that incorporating RFA results in slight rise in porosity and absorption while decrease in dynamic elastic modulus, ultrasound and thermal conductivity. Observations present an expectancy toward production of light-weight construction material contributing to significant environmental benefits.
13. Single-shot multibox detector- and building information modeling-based quality inspection model for construction projects
Identifying, locating, and evaluating concrete construction defects in the construction sector consumes time and is overlaid by subjectivity. This study proposes a single-shot multibox detector (SSD)-based and building information modeling (BIM)-based quality inspection framework to improve work efficiency and decrease unnecessary deviations resulting from human judgment. The SSD-based defect recognition model, which can identify surface defects with 86.56% average recall and 75.34% average precision, is trained using 1387 defect images of crack, honeycombing, water infiltration, rebar exposure, and edge or corner damage. Furthermore, a division algorithm is created to divide the BIM model surfaces into pieces, in which each piece is assigned with a unique location code number. After photographing a construction project according to the coding sequence, the defects in the images are identified and located on the BIM model. Then, the frequency of the quality defects, defect aggregation zones, and quality status in the BIM model are provided to the managers for fast-paced analysis. The case study results indicate that our inspection framework has the shortest inspection time and the highest kappa coefficients (0.816, 0.901, and 0.799) for crack, honeycombing, and reinforcement exposure prediction. The inspection accuracy of our model exceeds 98.5% for each defect. Our novel quality inspection framework can remarkably improve the efficiency and effectiveness of quality management and lead to a higher level of project management.
14. Unfired bricks prepared with red mud and calcium sulfoaluminate cement: Properties and environmental impact
To reduce the pollution brought by mud (RM), it is recycled for the preparation of unfired bricks by incorporating calcium sulfoaluminate (CSA) cement. The properties and the environmental impact were studied. The results demonstrate that, with the rise of RM content in the binary blends, the fluidity of the paste decreases, the water demand for normal consistency increases, and the setting time are shortened. The soluble Na in RM could promote the hydration of C4A3$ and C2S. Besides, RM could decrease the porosity of the hydration product of the binary blends. Therefore, RM could improve the compressive strength of the bricks. For the unfired bricks with 70% RM, the compressive strength satisfies the requirement in GB 5101-2017. The soluble Na and F could be immobilized by the precipitation of U phase, AlF3 and CaF2, respectively. The dissolution of the heavy metals and the radioactivity satisfy the requirements detailed in GB 5749-2006 and GB 6566-2010, respectively. Therefore, it is available to utilize CSA cement and RM to prepare an unfired bricks without bringing adverse environmental impacts.
15. Progressive collapse resistance of framed buildings with partially encased composite beams
Several research contributions stemmed from the increasing interest in progressive collapse-resistant design and assessment of structures, which was driven by extreme events all around the world. Most of studies focused on the robustness of steel and reinforced concrete (RC) structures, highlighting a knowledge gap on the progressive collapse resistance of framed buildings with partially encased (PE) continuous composite beams, which are an attractive solution compared to, for instance, their cast-in-place RC counterparts.
This paper presents the main outcomes of a numerical investigation that was aimed at evaluating/exploring the vertical load-carrying capacity of framed buildings with PE beams after column loss. A numerical fibre-based model was developed and successfully validated against experimental data on two full-scale composite beam specimens, indicating a high accuracy level of the models with displacement-based fibre elements. Then, a wide set of framed building structures with PE beams was generated according to Eurocodes, evaluating their progressive collapse resistance through the alternate load path method. Pushdown analysis was carried out to investigate the gravity load capacity under increasing downward displacement at the location of the removed column. Analysis results outline a huge sensitivity of progressive collapse resistance to the beam type (i.e. PE versus RC), beam depth and span length, with minor influence of longitudinal reinforcement in the case of PE beams. The peak load capacity under column loss was characterised at several limit states corresponding to increasing levels of damage, allowing the proposal of multiple regression models for progressive collapse design and assessment.
16. GraphCrypto: Next generation data security approach towards sustainable smart city building
Data confidentiality and integrity are essential security goals in the data communication in the smart city or similar applications. Despite significant changes in modern data communication systems and devices, the cryptosystems are still the primary option to achieve data security. Several cryptosystems have been developed, implemented and standardized to date. However, there is always a continuous demand for a new cryptosystem for providing security during data communication. In this paper, a novel symmetric cryptosystem is presented for achieving data confidentiality. The proposed cryptosystem is a graph-based system, where an algebraic structure of directed graphs along with a novel operation is defined to provide the base of the cryptosystem. Here, a directed graph represents a plaintext, a ciphertext, and a secret key as well. The defined operation is used for encrypting and decrypting plaintext and ciphertext graphs. The proposed cryptosystem provides a simplified transformation process and representation of plaintext to plaintext graph. The correctness of the proposed cryptosystem is validated, and also shown that the conventional brute-force approach to obtain the key from either plaintext or ciphertext is exponential and this computational time is significantly higher than AES. This implies that the proposed cryptosystem is highly secured against this attack. The proposed cryptosystem is implemented and compared with AES and the results infer that it incurs a marginally higher execution time than the AES for larger plaintext due to the involvement of matrix operations.
17. Influence of steel fiber size, shape, and strength on the quasi-static properties of ultra-high performance concrete: Experimental investigation and numerical modeling
This investigation focused on identifying the impact of various types of steel fibers on the quasi-static mechanical behavior of ultra-high performance concrete (UHPC) through different laboratory experiments as well as their numerical modeling. UHPC specimens were fabricated with four steel fiber types: ZP305, Nycon type V, OL 10mm, and OL 6mm. Fiber shape and size had little impact on quasi-static properties of UHPC in compression, while they showed significant impact on flexural and tensile properties. The main benefits offered by the smaller fibers occurred prior to reaching the ultimate load carrying capacity. Once the ultimate strength was reached, larger fibers were more effective in bridging larger cracks. Numerical modeling of the presented experiments were performed using the Lattice Discrete Particle Model (LDPM) enriched with fibers effect. LDPM is a meso-scale model simulating concrete at the scale of coarse aggregate pieces, and it has been extensively used for the simulation of concrete mechanical behavior under various loading and environmental conditions. The extension of this model, the so-called LDPM-F, developed for the simulation of fiber-reinforced concrete, is employed in this research to verify and better understand the experimental observations.
18. Strength characteristics and microstructure evolution of cemented tailings backfill with rice straw ash as an alternative binder
Cement is the most commonly used binder in mine filling materials, and it is a key to obtaining the desired mechanical properties of the backfill. However, cement costs often account for 75% of the total operational costs. The objective of this study was to use agricultural waste rice straw ash (RSA) to partially replace cement with a view to reducing the filling cost and yet improving the strength performance of cemented tailings backfill (CTB). The fluidity, strength characteristics, and microstructure evolution of CTB with different RSA replacement levels were measured through experiments. The results indicate the following: (1) The fluidity of the fresh CTB was reduced by the addition of RSA, but it could still ensure pipeline transportation. (2) The uniaxial compressive strength (UCS) of the CTB was positively correlated with the RSA replacement level. As the replacement level of RSA increased, compared to CTB without the RSA, the maximum increase of UCS of CTB with RSA was 46.2, 40.4, and 37.6% at 7, 14 and 28 d curing ages, respectively. (3) As the RSA replacement level increased, the strain in the compaction stage of stress–strain curve was decreased, and the elastic modulus of CTB with ARS was significantly improved. (4) The RSA consumed CH to generate additional C-S-H gel. The bonding strength within the tailings particles was enhanced, more compact microstructure was formed. Simultaneously, the micro aggregate filling effect of the RSA was conducive to further refinement of micro structure of CTB, thereby resulting in improvement of CTB strength. The research results have provided a theoretical and technical basis for the application of RSA in mine filling.
19. Influence of chloride contamination on carbonation of cement-based materials
An experimental investigation was conducted to understand the effect of the presence of chloride on the carbonation front. Microstructural analysis was conducted to verify the carbonation development in material previously contaminated by chlorides. Accelerated tests were combined to understand how the presence of chlorides influences carbonation front and how chloride test method influences in these results. The results indicate that the presence of chloride decreases the carbonation front in cement-based materials. This behaviour is related to the pore refinement and humidity retention caused by chloride. The impact on carbonation reduction occurs at different levels, according to the testing method used.
20. Three-dimensional evaluation method for asphalt pavement texture characteristics
To supplement the research on the evaluation method of asphalt pavement texture, novel three-dimensional (3D) methods are proposed. First, 18 different pavement textures were measured in laboratory from asphalt mixture specimens using laser texture scanner (LTS), and the macro-texture and micro-texture were extracted based on spectrum analysis techniques. Then, macro-texture level evaluation indices f8mac and f9mac together with micro-texture level evaluation indices f8mic and f9mic were proposed based on the gray level co-occurrence matrix (GLCM) method, and the determination of hyperparameters angle θ, pixel distance d and vertical resolution v were discussed. Through the correlation analysis and compared with existing conventional evaluation indices, the optimum pavement texture level evaluation index was selected and verified. Additionally, the evaluation index σ of distribution uniformity of pavement texture (DUPT) was proposed based on the uniformity of deviations between sub-surfaces and the average surface of pavement texture. Finally, the correlations of σ with texture profiles were studied. The results show that f8mac and f8mic are determined as the optimum indices for pavement texture level. Mean texture depth has significant correlation with f8mac, and the correlation coefficient R is 0.9611; friction coefficient μ has significant correlation with f8mic, and the R is 0.9422. θ is recommended to be 90°; d and v are set to 52 pixels (0.4953 mm) and 0.01 mm respectively for macro-texture level evaluation; d and v are set to 1 pixel (0.0095 mm) and 0.003 mm respectively for micro-texture level evaluation. Moreover, the effectiveness of σ is also validated by calibrating with standard grooved surface. It can be concluded that the proposed indices in this study are suitable to the evaluation of pavement texture level and pavement texture distribution.
21. Machine learning prediction of carbonation depth in recycled aggregate concrete incorporating SCMs
While recycled aggregates and supplementary cementitious materials have often been hailed for enhancing concrete sustainability, their effects on the resistance of concrete to carbonation has been controversial. Thus, deploying robust machine learning tools to overcome the lack of understanding of the implications of incorporating such sustainable materials is of paramount importance. Accordingly, this study proposes a gradient boosting regression tree (GBRT) model to determine the carbonation depth of recycled aggregate concrete incorporating different mineral additions, including metakaolin, blast furnace slag, silica fume, and fly ash. For this purpose, a database comprising 713 pertinent experimental data records was retrieved from peer-reviewed publications and used for model development and testing. Furthermore, predictions of the GBRT model were compared with calculations of available mathematical formulations to determine the carbonation depth in concrete. The results demonstrate that the machine learning methodology outperformed all the mathematical models considered in this study. The GBRT proved to be a robust tool that could be used to provide an insight into the resistance of concrete to carbonation and could be extended to predicting other features of concrete incorporating diverse recycled materials.
22. Effect of different aqueous solutions on physicochemical properties of asphalt binder
Aqueous solution is one of the main factors of asphalt pavement disease. However, the physicochemical changes of asphalt are ambiguous during immersion in different aqueous solutions. This study evaluated the physicochemical properties of asphalt under the action of different aqueous solutions to further understand the mechanism of moisture erosion. The morphology, chemical structure and four components of asphalt were observed after immersion, while the pH value, total organic carbon (TOC) and characteristic functional groups of residual solutions were monitored. The test results showed that aqueous solution could change the bee structure on the asphalt surface and increased the mean roughness. The carbonyl index (IC=O) and sulfoxide index (IS=O) of asphalt increased with immersion time. And the asphaltenes of asphalt fluctuated and eventually increased during immersion. Solute could accelerate the erosion on asphalt through interaction, the degree of which increased in the order, Na2SO4 saline < NaCl saline < pH 3 acid < pH 11 alkali.
23. Effect of rebar embedment length on the bond behavior of commercially produced recycled concrete using beam-end specimens
In a reinforced concrete element, the bonding of steel rebar in concrete is an important parameter as it affects its structural behavior. While using recycled aggregate to produce structural concrete, the attached mortar in the aggregate may affect the bond with deformed rebar. This study aims to investigate the bond behavior of deformed rebar in 100% recycled structural concrete produced from quality recycled coarse and fine aggregates while varying the embedment length from 200 mm to 300 mm. In this experiment, 20 beam-end specimens were tested to determine the bond efficiency of commercially produced recycled structural concrete and the results were compared with major design and descriptive equations found in ACI 408R03. It can be concluded that the average bond strength was conservative when compared with the design and descriptive equations. Moreover, three simplified descriptive bond strength equations using the ½, ¼, and ¾ root function formula of the compressive strength were proposed to complement the designing and detailing of reinforced recycled concrete structures.
24. Building condition assessment supported by Building Information Modelling
The buildings natural ageing along with the absence of planned maintenance actions and the effects of climate changes accelerate the building materials degradation. So, to extend the materials’ service life, the application of appropriate maintenance actions is imperative. This work aims to assess the building performance and to prioritize the maintenance actions employing Key Performance Indicators using Building Information Modelling-(BIM) as a supporting tool for Building Condition Assessment-(BCA) and maintenance management. To achieve these goals a methodology was proposed and applied to a case study involving 1) Building data collection; 2) Building Life Cycle Cost estimation, and 3) Automated calculation of Building Performance Indicator. This research application highlights the importance of BIM role in buildings’ Facility Management, allowing the model’s permanent update of information, in this case for BCA purposes. It also has high potential to prioritize the building maintenance actions, extending its materials service life, which contribute to attain a sustainable built environment.
25. Embodied emissions of buildings – A forgotten factor in green building certificates
The construction and use of buildings consume a significant proportion of global energy and natural resources. Leadership in Energy and Environmental Design (LEED) is arguably the most international green building certification system and attempts to take actions to limit energy use of buildings and construct them sustainably. While there has been a wide range of research mainly focused on energy use and emission production during the operation phase of LEED-certified buildings, research on embodied emissions is rare. The aim of this study is to evaluate the efficiency of LEED regarding initial (pre-use) embodied emissions using life cycle assessment (LCA). The study comprised several steps using a designed model. In the first step, three optional building material scenarios were defined (optimized concrete, hybrid concrete-wood, and wooden buildings) in addition to the base case concrete building located in Iceland. Second, an LCA was conducted for each scenario. Finally, the number of LEED points and the level of LEED certification was assessed for all studied scenarios. In addition, a comparison regarding embodied emissions consideration between LEED and Building Research Establishment Environmental Assessment Method (BREEAM) as mostly used green certificate was conducted in the discussion section. The LCA showed the lowest environmental impact for the wooden building followed by the hybrid concrete-wood building. In the LEED framework, wooden and hybrid scenarios obtained 14 and 8 points that were related to material selection. Among these points, only 3 (out of a total of 110 available points) were directly accredited to embodied emissions. The study recommends that the green building certificates increase the weight of sustainable construction materials since the significance of embodied emissions is substantially growing along with the current carbon neutrality goals. As most of the materials for building construction are imported into Iceland, this study is useful for locations similar to Iceland, while overall it is beneficial for the whole world regarding climate change mitigation.
VẬT LIỆU XÂY DỰNG
1. Flexural behavior of sandwich panels combining curauá fiber-reinforced composite layers and autoclaved aerated concrete core
The mechanical response of sandwich panels with two layers of curauá fiber cement composites and a core layer of autoclaved aerated concrete (AAC) was investigated. Each layer consisted of long unidirectional curauá fibers and a cementitious matrix. For durability purposes, 50% of the Portland cement was replaced with pozzolanic materials to reduce the content of calcium hydroxide in the matrix. The performance of sandwich panels with 350 mm × 60 mm × 90 mm (length × width × thickness) was evaluated through monotonic and cyclic four-point bending tests to obtain the load–deflection response, flexural strength, and toughness. Monotonic bending tests were performed on each component of the panels – i.e., composites and AAC blocks. Pull-off tests were performed to evaluate the adhesion between the skin layers and the core, while optical and scanning electron microscopes were used to observe the interface’s topography. The results revealed the externally bonded layers’ efficiency, which provided a higher deflection capacity to the material and increased its flexural strength. The AAC blocks revealed a more ductile response when assisted by the composite layers in the sandwich structure. Under cyclic bending test conditions, the sandwich panels exhibited a satisfactory post-peak ductility so that the energy was not abruptly lost but gradually released throughout its deflection-softening behavior.
2. Corrosion-induced cracking propagation of RC beams subjected to different corrosion methods and load levels
Corrosion-induced concrete cracking is a major phenomenon of structural deterioration, useful to appraise durability of structures in service. In this work, beam specimens subjected to loads were corroded by drying-wetting cycles and the impressed-current accelerated method. Three types of corrosion-induced cracks and the strong constraint effect of stirrups were found. The cracking process was divided into two stages by the appearance of a penetrating crack; the crack length ratio had a leap at the critical time. Accelerated corrosion test results underestimated the cracking damage of natural conditions. Furthermore, the larger load accelerated the formation and propagation of penetrating crack.
3. Synergetic effect of two inhibitors for enhanced corrosion protection on the reinforcing steel in the chloride-contaminated carbonated solutions
The synergetic inhibiting effect of benzotriazole (BTA) and Na2HPO4 for the corrosion of reinforcing steel in the chloride-contaminated carbonated solutions was preliminarily investigated by electrochemical measurements, as well as X-ray photoelectron spectroscopy and scanning electron microscopy/energy dispersive X-ray techniques. Results show that a mixture of BTA and Na2HPO4 acts as an anodic inhibitor. An optimum enhanced inhibition efficiency was obtained for a mixture of 0.05 M BTA and 0.05 M Na2HPO4. The synergistic inhibiting mechanism for steel was proposed, which was by forming a protective film consisting of Fen(BTA)m complex and iron phosphates, as well as hydrogen bonding between them on the steel surface. On the contrary, a mixture of unequal amount of BTA and Na2HPO4 showed an antagonistic effect on corrosion inhibition resulting from the competition between the phosphate ions and BTA– on the steel surface.
4. Generation of virtual asphalt concrete in a physics engine
The precise, quick and efficient simulation of asphalt concrete is an important step to select asphalt mixtures for a range of applications. A method to create virtual aggregates based on aggregates’ topological properties and aggregate skeletons like those of asphalt concrete using a physics engine is proposed. It can produce hundreds of virtual aggregates with shape properties equivalent to these of real ones in a matter of seconds, pack them to a level of compaction like that of the Marshall compactor, and measure properties such as the expected air voids content and number of contacts between the aggregates. In the paper, only aggregates bigger than 2 mm have been considered due to computing efficiency. Besides, it was found that the main factors influencing asphalt compaction are the number of aggregates in the mixture and the amount of dust, or aggregates smaller than 2 mm, which correspond to the parts of the solid skeleton that have not been simulated.
5. Behaviour of screw connections in timber-concrete composites using low strength lightweight concrete
In this paper, the use of low strength lightweight concrete in combination with glue-laminated timber (TLCC) is studied. Six series of push-out tests were conducted to assess the mechanical performance of the screw shear connection between these materials with a perpendicular and inclined (shear-compression) configuration with various screw diameters and lengths. The tests show that though low strength lightweight concrete is used, composite action can still be obtained. Given the equivalent Young’s modulus between the concrete and the timber, a proposal is made consisting in the use of the design approach for timber-to-timber connections in order to determine the load capacity of the tested connections, contrary of what is commonly used in the literature. The comparison with experimental tests confirm the proposed approach.
6. Impact of calcium leaching on mechanical and physical behaviors of high belite cement pastes
Water conservancy engineering such as dams and canals built with high belite cement (HBC) concrete for reducing temperature cracks have been running for many years and are still constantly under construction. However, little research has been conducted on the calcium leaching behaviors of HBC. In this paper, mechanical and physical properties such as mass loss, porosity, leaching depth, compressive strength and hardness of HBC-based pastes (with three w/b ratios and contents of fly ash) exposed to ammonium chloride aqueous solution were measured. In addition, slice specimens of HBC and ordinary Portland cement (OPC) were designed to study their Ca/Si ratio changes in leaching process, XRD, SEM and EDS mapping scanning were also carried out to investigate the variations of composition and microstructures between degraded and intact cement hydrates. Results show that the macro-properties of leached HBC pastes are similar to but slightly worse than those of OPC, while there is a lower calcium leaching rate of HBC in both stages of CH dissolution and C-S-H decomposition. Furthermore, the w/b ratio has an appreciable effect on the physical and mechanical performance of HBC pastes subjected to leaching, and the corrosion damage could be alleviated by adding fly ash. Eventually, a distribution model of Vickers hardness based on Logistic function is proposed to evaluate the degradation of leached pastes with high accuracy, and the axial compressive strength could be quantified by equivalent Vickers hardness with a well linear relationship.
7. Preparation and mechanical properties of asphalt mixtures reinforced by modified bamboo fibers
Cracking resistance and durability are the main concerns in asphalt mixture for pavement. The addition of fibers is an effective way for reinforcing asphalt mixture. Bamboo fibers (BFs) show unique characteristics such as high specific strength and modulus, renewability and low cost. Thus, BFs mechanically extracted from green bamboos were used to improve the mechanical properties of asphalt mixture and thus increase the service life of asphalt pavement. For improving the poor interfacial adhesion resulted from the hydrophobicity of asphalt and the hydrophilicity of BFs, a melamine–formaldehyde (MF) copolymer was synthesized and used to modify the BFs. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectronic spectroscopy (XPS), and nuclear magnetic resonance (NMR) analyses were conducted to reveal the surface chemistry of BFs. The results proved that the MF copolymer was grafted onto the surface of BFs via the formation of covalent bonding between hydroxyl groups of BFs and amino group of melamine. The mechanical properties of the asphalt mixture were evaluated by Marshall stability, direct tensile, and indirect tensile tests. Results showed that the addition of modified BFs increased the stability and the tensile strength of the asphalt mixture. SEM images of the fractured surface of asphalt mixture indicated that strong adhesion was formed between the modified BFs and asphalt matrices.
8. Performance of geopolymer tiles in high temperature and saturation conditions
High temperature and saturation situations are conditions that a building material can experience due to fire, heavy rains and floods, for example. For this reason, the application of geopolymer tiles in conditions of high temperature and saturation was evaluated in this work, to understand how fires and rains modify the performance of these materials. Samples were produced varying the molar ratio of SiO2/Al2O3 between 2.25 and 4.00, curing at an ambient temperature of 25 °C at 7 and 28 days. Metakaolin, sodium hydroxide, sodium silicate and water were used as raw materials in this study. Initially, the samples were evaluated in normal condition performing tests of flexural tensile strength, linear shrinkage, density, optical microscopy (OM) and mineralogical analysis. It was found that formulations 2.25, 2.50 and 3.00 had compatible properties, while formulations 3.50 and 4.00 did not show efficiency in the geopolymerization reaction due to the excess of sodium in the material. Formulations 2.25, 2.50 and 3.00 formed larger amounts of zeolite A (sodalite cage) and zeolite X (faujasite), which are minerals formed after the geopolymerization reaction. This did not happen with formulations 3.50 and 4.00. In the sequence, the high temperature condition was carried out until the temperature of 1050 °C, being carried out tests of burning linear shrinkage, mass loss, flexural tensile strength and thermal analysis. The results showed that due to the non-formation of polysialate networks in an effective way, formulations 3.50 and 4.00 showed a high drop in properties, differently from formulations 2.25, 2.50 and 3.00, that present efficient polysialate networks, due to the formation of zeolites X and zeolites A. Finally, the saturation condition was performed, where open porosity, water absorption, OM and flexural tensile strength were evaluated. It was observed that the formulations 3.50 and 4.00 showed elimination of sodium gels during saturation, which caused a decrease in the mechanical performance of the material. In all conditions, formulations 2.25, 2.50 and mainly 3.00 showed better results. Finally, geopolymers tiles with SiO2/Al2O3 = 3.00 was evaluated in a complementary manner by scanning electron microscopy (SEM), where it proved its compatibility with the application proposed in this work.
9. Biomaterials heterogeneous displacement, strain and swelling under hydric sorption/desorption: 2D image correlation on spruce wood
Spruce wood, as all biosourced materials, is very sensitive to relative humidity changes, which can cause dimensional variations. In some cases, it leads to eccentricity, degradation and deterioration of the wooden structures. The 3D methods of evaluation of the spruce wood hydric behavior needs important financial resources and investigation. That’s why, the main objective of this study is to develop the technics of 2D digital image correlation to estimate the local displacements and strains values under hydric solicitations and to follow the hysteresis phenomenon, anisotropy and swelling coefficient. In this context, cycles of sorption – desorption for relative humidity that vary from 0 to 100% were applied. Results represent swelling coefficients for early- and latewood as a function of wood directions. A particular attention was devoted to the uncertainty of the 2D digital image correlation technics for both earlywood and latewood. This study provides the literature and future research with promising results especially concerning the evolution of the microscopic morphology of biosourced materials when exposed to relative humidity variations, which can significantly affect their macroscopic behavior.
10. Improving elevated temperature performance of geopolymer concrete utilizing nano-silica, micro-silica and styrene-butadiene latex
Geopolymer binders (GPBs) have gained an increasing research potential in recent years due to their environmental, economic and durability advantages. This paper aims to improve elevated temperature performances of volcanic tuff (VT) based geopolymer concrete (GPC) by utilizing nano-silica (NS), micro-silica (MS) and styrene-butadiene latex (SBL). To this end, NS, MS and SBL additives were added to GPC samples at 2%, 2% and 5% ratios by weight of binder, respectively. GPB was obtained by activating ground VT with 12 M NaOH solution. Produced GPC samples were exposed to elevated temperatures (100, 300, 500 and 700 °C) for 1 h after reaching the target temperature. Changes in compressive strength, water absorption, visual appearance, weight and microstructure of GPC samples were investigated after the influence of elevated temperatures. The experimental findings displayed that compressive strength of GPCs increased up to 300 °C independently of the type of additive used, but higher temperatures than 300 °C caused decrease in compressive strength values. As a result of mechanical tests and microstructure investigations, it was determined that MS additive significantly increased the elevated temperature performance of GPCs. Additionally, color of GPC samples turned gray after elevated temperatures due to dehydration of GPB and microstructural transformations occurring in aggregates.
11. Sequestration of carbon in pedogenic carbonates and silicates from construction and demolition wastes
Progressive diffusion of CO2 into cement-based construction products and consequent carbon uptake has received considerable attention in recent years. Studies have promoted the capacity of soils mixed with construction cement wastes to function as a carbon sink, which has largely been overshadowed in emissions inventories. There is however little consensus on reversal of carbonation in urban soil systems – that is rooted in uncertainties as to the geo-chemo-mechanical properties of recent carbonates in relation with environmental factors and carbon sequestration. Here, we present preliminary findings from a study of pedogenic and anthropogenic calcium carbonates. In phase 1, we simulate precipitation and weathering of pedogenic and man-made (Ánthropōcalc) carbonate artefacts. We show that carbon cycles through pedogenic carbonates to reprecipitate snowflake shaped, marginally more soluble, secondary carbonates that occupy the macro-pore spaces. Greater carbon is stored in larger Ca2+ sinks. We show that precipitation of carbonates in basic environments containing abundant Na+ yields aragonites like carbonates and Ánthropōcalc artefacts. These are nanometric needle-fibre units that agglomerate into microrods and drape the pore network, lending a high potential of collapsibility. Precipitation of carbonates in acidic environments yield snowflake shaped secondary carbonates of substantially lower collapsibility. These suggest the dominant impacting of pH on shape, form and stability of secondary carbonates, thus opposing the common perception of Ánthropōcalc’s outright stability. In phase 2, we refer to data compiled from block specimens collected from a demolishment site. Long-term exposure to rubble, where sequestration has taken its toll, yields a rise in soil solution pH. Collapsibility increases despite a clear reduction in calcite content and porosity – this is attributed to the meshwork of rodshape elements, dominantly phyllosilicate with needle-shaped Ánthropōcalcs within the inter-particle space as registered by peaking calcium and oxygen in the EDS data. Data from samples from vegetated sites and in vicinity of rubble highlights a mechanism whereby, Ánthropōcalcs from carbon sequestration in silicates gradually evolve and change in shape and solubility in response to reduced pH.
12. Reconstruction of fracture geometry in material medium by elastic wave
Over the past few years, intelligent detection and fast and precise positioning for fracture have been hotspots in the field of geological engineering. The propagation of elastic wave in fracture inclusive one-dimensional line segment was obtained through simulation, and then Densely Connected Convolutional Networks (DenseNets) were used to learn waveform. Moreover, the key features of the fracture were obtained automatically from elastic wave to achieve fast, precise, and intelligent detection for fractures in line segment. Furthermore, the Schoenberg linear slippage model was used to describe the contact behavior of closed fractures on two-dimensional plane. The propagation of elastic wave on fracture inclusive plane was obtained by simulation, and the plane is divided into several horizontal and vertical straight lines in which elastic wave was collected. The sampled data were analyzed by the trained neural network model, and geometrical reconstruction was implemented for fractures on the plane based on the detection results of each line and row. Finally, three-dimentional scanning laser Doppler vibrometry was used to experimentally obtain propagation of elastic wave on granite plane under incentive effect, and then experimental data were input into the neural network. This has accurately recovered the geometrical shape of fracture in granite and further verified the precision of the neural network.
13. Recycling of industrial and agricultural wastes as alternative coarse aggregates: A step towards cleaner production of concrete
Aggregates are mined on a larger scale leading to the depletion of mountains and ecosystem. Cleaner production of artificial stone aggregates from industrial waste is an alternative to natural stone aggregates. Although earlier studies have reported the use of artificial aggregates, a comprehensive review of the performance of alternative aggregates in concrete is highly limited. Therefore, the present review focuses on reusing waste materials from the agricultural and industrial sectors to produce alternative coarse aggregates. The effect of coarse aggregate replacement with agricultural and industrial wastes like furnace slag, oil palm shell, coconut shell, waste ceramic tiles, glass, expanded polystyrene, lightweight expanded clay aggregate, and recycled concrete aggregate on fresh, hardened and durability properties of concrete is reported. Moreover, a critical evaluation of sintered and cold bonded artificial aggregate production processes and their influence on concrete properties is also presented. Recycled concrete aggregates, oil palm shell, and expanded polystyrene resulted in the increased workability whereas, the addition of ceramic waste and steel slag as coarse aggregates reduced the workability of concrete. The workability of concrete depends mainly on the water absorption of alternative aggregates used. Characteristics of artificial coarse aggregates depend on binder type and binder dosage adopted in the production process. The properties of sintered aggregates are governed by sintering temperature. Lower crushing strength of alternative coarse aggregates resulted in a subsequent reduction in the compressive strength with an increase in the replacement level. Reduction in the density of concrete is witnessed in sintered and cold bonded aggregates used concrete.
14. Experimental verification of 2- and 3-D numerical models for bond-slip behavior of CFRP-concrete
This paper studies the bond performance between fiber-reinforced polymer (FRP) and concrete using two variations of the double shear lap test setups. Experimental tests were conducted followed by a series of finite element simulations using cohesive zone model. The experiment utilized an improved double-pull shear setup with the tests conducted on specimens of varying FRP-concrete bond lengths. The numerical simulations were carried out for the improved as well as the traditional setups using two converged meshes with both 2- and 3-D spatial idealizations to study their relative performance. The results are discussed in light of the damage mechanism, load–displacement, strain and stress distribution, bond-slip behavior, and fracture energy. The tested specimens show no effect of bond length variation on the FRP-concrete interfacial strength so long as the bond length exceeds the effective bond length – Only the case of bond length lower than the effective bond length shows otherwise. The study also succeeds in validating the 2- and 3-D numerical simulations using the experiments in both the two cases of spatial idealizations and the two types of test setups in terms of strain and stress distributions, bond-slip curve, and fracture energy. However, while the 3-D models succeed in capturing the failure load accurately, the 2-D models fail to do so. Evidence of similar performance between the improved double shear test and traditional double shear test setups reaffirms the fact that the former could be used to replace the latter.
15. Preparation and properties of ready-to-use low-density foamed concrete derived from industrial solid wastes
Foamed concrete is widely used as a highly energy-efficient building material. However, low-density foamed concrete requires increased amounts of Portland cement or steam curing to meet engineering requirements. This is due to inadequate compressive strength and long setting time of Portland cement. In this study, we investigate a method for preparing green, high strength, low-density foamed concrete, which is ready to use without the application of heat or pressure. First, a sulfoaluminate high-activity material (SHAM) was prepared using red mud, aluminum dust, flue gas desulfurization-gypsum, and carbide slag. The SHAM was used to produce ready-to-use low-density foamed concrete (RLFC). RLFC with a dry density of 615 kg/m3 had a compressive strength of 4.11 MPa and a thermal conductivity of 0.1638 W/m·K. Addition of 0.2 wt% hydroxypropyl methylcellulose (HPMC) as foam stabilizer, increased the compressive strength by 27.22% to 5.22 MPa, which was 3.48 times the compressive strength specified by the relevant Chinese standard (1.5 MPa). To further enhance the practicality, other solid wastes (limestone tailings and gold tailings) were blended with SHAM to prepare the RLFC. RLFC prepared from SHAM, limestone tailings, gold tailings, and HPMC in the match ratio of 54:6:40:0.11 (wt%) delivered dry density, compressive strength and thermal conductivity values of 612 kg/m3, 2.37 MPa and 0.1556 W/m·K, respectively. This study provides a low-cost and highly promising method for preparing low-density foamed concrete, which not only consumes a large amount of industrial solid waste but also avoids depletion of resources and generates profits.
16. Structural characteristics of load bearing straw bale walls
Straw bales offer a renewable and affordable construction material suitable for a range of uses as both thermal insulation in walls and roofs, and for low rise loadbearing structural walls. As a co-product of food production, it places no further pressure on land use, and in common with other crop-based materials, straw captures and stores carbon dioxide through photosynthesis, offering the means to construct buildings with a net negative carbon emissions footprint. Straw also further reduces operational carbon emissions by virtue of its excellent thermal resistance. However, despite these benefits, and a successful construction history extending over 100 years in many countries worldwide, straw bale construction has still to make a major commercial impact in the wider construction market. Limited technical understanding of some fundamental performance characteristics (including structural capacity, hygrothermal behaviour, and durability), absence of technical standards, and a lack of certification and product warranty for straw bale, still remain barriers to wider acceptance. In this paper results are presented from a study on full-scale straw bale walls to evaluate the structural performance under vertical loading and lateral loading. The performance of identical straw bale walls, with and without plaster coats, is presented. The study is also unique in presenting on out-of-plane lateral loading and wall performance under eccentric vertical load cases. The research will support structural designers and enable wider uptake of this sustainable form of construction.
17. Influence of quasi-static strain rate on the stress-strain characteristics of modern reinforcing bars
While it has been known for decades that even for quasi-static loading, increments in strain rate lead to increased stresses in the inelastic range, this effect is often ignored. However, accurate knowledge of the stress-strain characteristics of reinforcing bars is an indispensable prerequisite for the safe design of new structures and the realistic assessment of the structural safety of existing ones, and the strain rate dependency of the reinforcing steel characteristics should thus be accounted for in many situations. An exemplary case is quality control: Reinforcing bars produced today are periodically tested to check their conformity with specifications, determining their stress-strain characteristics in standard tensile tests. However, the applied quasi-static strain rates may vary considerably, but are not commonly reported. Hence, the results are subject to considerable uncertainty. Another relevant case is the structural safety assessment of existing structures affected by local corrosion of the reinforcement: Their cross section (and hence, stiffness) varies considerably along the bar axis and consequently, the strain rate in corroded sections is significantly higher than in non-corroded sections, leading to higher yield stress and tensile strength.
This study investigates the effect of quasi-static strain rates on the stress–strain characteristics of modern reinforcing bars based on a comprehensive experimental campaign. In four series of experiments, 41 tensile tests on three different types of reinforcing bars were conducted, applying strain rates between 0.004 ‰/s and 1.0 ‰/s. Compared to the static stress, an increase of up to 8% in the dynamic stress was observed, depending on the type of reinforcing bar. Based on these observations, a simplified model for the strain rate dependency was developed and validated against experimental data, showing excellent agreement.
18. Experimental study on mechanical properties of corroded stainless-clad bimetallic steel bars
The mechanical properties of stainless-clad bimetallic steel bars (SCBSBs), which consist of S30408 stainless steel as the cladding metal and HRB400 carbon steel bars as the substrate, were experimentally investigated. The results of a tensile coupon test indicated a clear yield plateau in the stress–strain curve of the SCBSBs. The metallurgical bonding ensured stable composite working performance between the cladding layer and the substrate. Accelerated electrochemical corrosion was performed to obtain different corrosion degrees in the SCBSB specimens, and their mechanical properties were investigated. The corrosion performance of SCBSB specimens with different corrosion degrees was introduced. The experimental results indicated that an increase in the degree of corrosion resulted in a decrease in yield strength (fy), ultimate strength (fu), ultimate strain (εu) and elongation percentage (δ). The adverse effects of corrosion on the fy, fu and εu were quantified through the proposed linear formulae. A nonlinear formula was proposed to predict the relationship between the degree of corrosion and δ for the SCBSBs. Furthermore, a comparison between the SCBSBs, homogeneous carbon steel bars, and stainless steel bars with different corrosion degrees was conducted. Based on the minimum required values of fy, fu, and δ as per the GB/T 1499.2–2018 standard, the corrosion degrees of the SCBSB should be restricted to 13.9%, 14.6%, and 27.7%, respectively.
19. The effect of pre-treatment and curing temperature on the strength development of alkali-activated clay
This paper reports the strength development in alkali-activated clay (AAC) synthesised from untreated and calcined low grade clays. The effects of clay calcination and the temperature adopted in different curing regimes on the mechanical properties of AAC were studied from a microstructural viewpoint. Solid-state MAS NMR, FTIR, EDS, and TEM imaging were used for the microstructural studies. Calcination of the clay resulted in an increase in the 7-day compressive strength of AAC from 31.7 MPa to 47.8 MPa. 29Si MAS NMR results indicated that ratio of Q4(2Al) percentage to Q4(4Al) percentage correlates positively with the compressive strength. Curing the AAC at higher temperatures resulted in higher strength, but there was a conflict between strength development due to ongoing polymerisation and strength deterioration due to post-curing crack propagation. FTIR results indicated the formation of a more polymerized structure and stronger bonds in the AAC as a result of calcination. In addition, FTIR showed a higher Si–O bond strength in AAC cured at a higher temperature, which positively correlated with the compressive strength of the specimens. EDS and TEM results revealed the presence of a silicon-rich phase in AAC synthesised from the untreated clay. This sodium silicate gel exhibited poor hydrolytic stability which could result in long term durability issues.
20. Production of lightweight aggregate ceramsite from red mud and municipal solid waste incineration bottom ash: Mechanism and optimization
Red mud (RM) and municipal solid waste incineration bottom ash (MSWIBA) are continually generated in large amounts all over the world. In this study, RM and MSWIBA were made into pellets by a disc pelletizer and then transformed to lightweight aggregate ceramsites by high-temperature sintering. The sintering mechanism and optimal production process were revealed from evaluation of the performance of ceramsites produced under different production processes. The results showed that as the proportion of RM increased, the required sintering temperature increased at least by 7.34%, while the apparent density, bulk density, strength, porosity, proportion of macropores and pH of ceramsites reduced up to 9.46%, 9.45%, 68.56%, 77.36%, 93.75% and 3.43%, respectively. On the other hand, with the increase in sintering temperature, the apparent density and bulk density of ceramsites made from calcium-rich red mud (CRM) generally increased while the water absorption and pH generally decreased. The strength, however, first increased up to 27.11 MPa and then decreased to 17.48 MPa. When the ratio of MSWIBA and CRM was 1:1 and the sintering temperature was 1070 °C, the ceramsites produced could achieve the best performance with a bulk density of 1046.73 Kg/m3, an apparent density of 1783.44 Kg/m3, a particle strength of 27.11 MPa, a 1-hour water absorption rate of 0.8%, and a pH of 8.9. The ceramsites, for use as lightweight aggregates, can be a promising construction material in particular counting the benefits of waste recycling.
21. Effects of composite geometric characteristics of coarse particles on interface interactions of aggregate-asphalt system
The complex geometric morphologies and contact status of aggregate particles and the interface interactions between aggregate and asphalt significantly affect the compaction properties and mechanical response of asphalt mixtures. The spreading-combination method was proposed to build the calculation model of composite geometric indexes to quantitatively characterize the composite geometric characteristics of the particle system. The effects of composite geometric characteristics on the interface interactions of the aggregate-asphalt system were analyzed adopting the contact-slip tester. The results indicate that the measures of shape, texture, and angularity respectively denote perimeter, surface area, and volume. The composite shape index is primarily affected by the number of particles. Smaller-sized coarse aggregates and fine aggregates exercise a greater impact on the composite texture index, while the composite angularity index is more sensitive to large-sized coarse aggregates. The fine particles attach to the surface of coarse aggregates, diminishing the contributions of the composite texture characteristics of coarse aggregates to the particle contact strength of the particle system. The larger the composite angularity index, the more significant the lubricating effect of asphalt on particle contact. However, asphalt can transform a part of the interference effect of the fine aggregates into the bonding effect of the skeleton. The composite angularity index is positively correlated with the skeleton bonding index, which can be used to evaluate and predict the interface interactions of the aggregate-asphalt system.
22. Residual mechanical strength of concrete exposed to high temperatures – international standardization and influence of coarse aggregates
The exposure of concrete to high temperatures affects its mechanical properties, reducing its compressive strength, tensile strength and modulus of elasticity. The reduction factors of these properties have been the target of several studies over the years, producing conflicting results. This article addresses the key factors related to such disparity, highlighting the influence of standardization and types of coarse aggregates, as well as an overview of the study of the mechanical properties of concrete exposed to high temperatures in the last years, foregrounding research in several countries and Latin American experience. This article also shows results from a Brazilian experimental study concerning the residual mechanical strength of concrete (NSC and HSC) exposed to temperatures from 100 to 900 °C at 1 °C/min, with or without preheating, in which three types of coarse aggregates—basaltic, granitic and limestone—were used, as well as RILEM recommendations. There is no precedent in Latin America for a study conducted for this purpose and which has applied such international recommendations. Through comparison with bibliographic references and statistical analysis, the effects of the type of coarse aggregate, preheating of samples and types of addition being used were evaluated, contributing to the structural analyses of burning structures.
23. Multi-scale study of bio-binder mixtures as surface layer: Laboratory evaluation and field application and monitoring
The potential use of bio-binders as full or partial substitutes of petroleum-based binders have gained interest from the paving researches in recent years. Although there are many studies about rheological characterization of alternative binders, there is still lack of knowledge about mixtures and field performance of this type of materials. In this sense, this paper presents an evaluation of bio-binder produced from vegetal biomass, by-product of the treatment of pine wood resin, as the total substitute of the asphalt binder for surface pavement layer, comparing its performance with a neat asphalt binder, used as reference, at three study levels: binder evaluation, mixture evaluation and field performance monitoring. Linear viscoelastic characterization, permanent deformation and fatigue responses were studied for the binders. The mixtures designed with both binders were tested in terms of stiffness, moisture sensitivity and permanent deformation. The performance in the field test sections was monitored during three years by structural evaluation (FWD) and roughness test (IRI). Results showed that the bio-binder studied presented acceptable behavior, with similar responses of that exhibited by the petroleum-based asphalt binder. The bio-binder studied could be used as binder in mixtures for surface layers of road pavements, however, the durability of that type of mixtures and the environmental impact of the production process need to be further studied in order to complement the feasibility of this alternative as a sustainable solution.
24. Long-term loading and recovery of a laminated glass slab with three different interlayers
The mechanical behaviour of laminated glass plates and beams is affected in different ways by the shear stiffness of interlayer materials. Polymeric interlayers are viscoelastic materials, and therefore experience creep when subjected to long-term loading. In this paper, three laminated glass panels, each with a different interlayer material (PVB Clear, PVB ES, and SentryGlas), were placed between two laminated glass beams. A uniformly distributed load was applied during four months to study the effect of creep, and then was removed to see the deflection recovery during one month. The midspan vertical displacement of the two laminated glass beams remained almost constant over time, with a small variation that was attributed to the rubber sheets placed in the supports. The plate with SentryGlas had the lowest elastic deformation, creep, and residual deformation. The plate with PVB Clear had the highest elastic and total deformation. The plate with PVB ES had a similar initial deflection as SentryGlas, but was the one that experienced the highest creep. At the end of the test the plates still had a small residual deflection, which could be due to an incomplete deflection recovery. The flexural behaviour of the three laminated glass plates was simulated using a Finite Element Model, representing the loading, the creep, the unloading, and the deflection recovery stages.
25. Influence of effective texture depth on pavement friction based on 3D texture area
Pavement texture significantly affects the anti-skid performance. This study applied 3D laser technology to measure the texture of asphalt pavement surfaces with an objective to explain the variation in the friction measured using a portable pendulum tester. Pavement slab samples were prepared for six different types of asphalt mixtures (SMA-Top5, AC-10, AC-13, AC-16, SMA-13, and OGFC-13). High-precision surface texture data of the samples were then collected using a portable laser scanner (LS-40), and the friction values (BPN) were measured. The 3D image reconstruction and segmentation of the pavement texture were realized through a digital image processing technology, and the texture surface area at different depths was calculated. Finally, we performed a correlation analysis between the texture surface area at different depths and the pavement friction values. The results showed that the pavement anti-skid value and the texture surface area have a significant positive correlation in the texture depth range of 0.5–2 mm, with the lowest determination coefficient value of 0.6836. Our research confirms that the effective texture depth influencing pavement friction is 2 mm and that the texture surface area can be used as an indicator of pavement friction during its service life.
26. Development of a coherent framework for balanced mix design and production quality control and quality acceptance
Asphalt mixtures are becoming increasingly complex, and given ever-changing components of asphalt mixtures, both balanced mix design (BMD) and production quality control and quality acceptance (QC/QA) are critical to have a mixture performing well in the field. This paper established a coherent BMD/QC/QA framework that has four inter-connected components: (1) volumetric mix design and selection of multiple asphalt contents for mixture performance evaluation, (2) mixture performance evaluation at multiple asphalt contents and selection of the balanced asphalt content, (3) mixture performance verification at the balanced asphalt content, and (4) production QC/QA testing. One set of laboratory tests and associated acceptance criteria are recommended for the mixture performance evaluation and the production QC/QA testing and the other set for the mixture performance verification where DOTs can choose their preferred performance verification tests. Furthermore, two practical loose mixture aging protocols are developed, one for short-term aging used in the process of the volumetric mix design, the mixture performance evaluation, and the production QC/QA testing and the other for mid-term aging employed in the mixture performance verification. The recommended short-term aging protocol is to age the loose mixture in a force draft oven for 2 hrs at the mixture compaction temperature, while the mid-term aging protocol consists of three steps: (1) short-term aging, (2) 20 hrs loose mixture aging at 100 °C, and (3) reheating to for compaction. A case study is presented at the end of this paper to demonstrate the whole process of the framework including the actual plant production QC testing.
27. Improvement on rheological property of asphalt binder using synthesized micro-encapsulation phase change material
Temperature is a governing parameter that affects the rheological property of asphalt binder. Upon cooling, bitumen becomes stiffer and prone to thermal cracking. To reduce the negative impact of temperature, utilizing the thermal energy storage of phase change material is a promising solution. This study provides an approach to synthesize micro-encapsulation phase change material (μPCM) and its application to enhance the binder’s rheological property and mitigate black ice. Two μPCMs were prepared with n-Tetradecane as a core, while Calcium carbonate (CaCO3) and Silicate (SiO2) as a shell. SEM test exhibited that μPCM had a spherical shape with a diameter ranging from 1 to 7 μm. Meanwhile, thermogravimetric analysis proved that the encapsulation method could protect and prevent leakage of n-Tetradecane under high temperature. The residual weight of CaCO3-μPCM was 95% and 84% at 160 °C and 350 °C, respectively. The differential scanning calorimeter results showed that the encapsulation ratio was approximately 52.9% (ΔH = 99.94 W/g). Moreover, different μPCM modified asphalt binders were examined to evaluate the rheological property. Results from rotational viscosity test at 135 °C pointed out that adding μPCM did not affect binder viscosity. DSR test showed that the incorporation of μPCM could reduce binder stiffness at low temperatures. The thermal effect of μPCM was analyzed by low-temperature sweep test. With simultaneous cooling, μPCM released latent heat, thus increasing the binder’s temperature by 1.5 °C. The low values of G*sinδ indicated the outperformance of μPCM-binder compared to conventional binder in terms of thermal cracking resistance.
28. Physical and mechanical properties of sustainable vegetal concrete exposed to extreme weather conditions
This paper studies the durability properties of vegetal concrete exposed to extreme environmental conditions including immersion weathering, outdoor weathering, salt attack, and freeze-thaw attack. Magnesium phosphate cement (MPC) binder containing high percentage of red mud and fly ash was mixed with the corn stalk based vegetal aggregates. It was found that all samples exposed to immersion weathering, outdoor weathering, and freeze-thaw attack showed a loss in mass, reduction in sample area, and decrease in compressive strength, which was associated with the dissolution and leaching out of the binder. Increase in the mass and swelling was observed for the vegetal concrete mixtures immersed into salt solution due to formation of salt layer on the surface of binder and vegetal aggregate. It was concluded that incorporation of fly ash, high compaction of samples, and pretreated aggregates improved the durability performance of vegetal concrete against extreme weather conditions.
29. Mechanical properties of low-carbon ultrahigh-performance concrete with ceramic tile waste powder
In this paper, ceramic tile waste powder (CTWP) was used to replace cement in to prepare whole-life low-carbon ultrahigh-performance concrete (UHPC). The mechanical properties, modification mechanism, environmental impact and cost of UHPC with 15–55% CTWP were investigated. The results indicated that the compressive and flexural strength of the UHPC with CTWP are all higher than 120 MPa and 14 MPa at 28 d within the error range, respectively. The mechanical properties of UHPC with 35% CTWP maximally improved at 28 d, while the mechanical properties of UHPC with 55% CTWP all decreased by less than 10% at 28 d. The modification mechanism of CTWP on UHPC mainly included the pozzolanic effect, nucleation effect and filling effect, which were proven by pozzolanic activity analysis, TG-DTA, SEM and MIP. CTWP possesses pozzolanic activity and can improve the hydration degree of cement by as much as 51.4%. Furthermore, the addition of 35% CTWP decreased the ITZ, total porosity, and number of mesopores of UHPC by 15.70%, 4.38%, and 42.04%, respectively. Moreover, environmental impacts and cost analysis were also performed, and the energy intensity, CO2 emissions, and material cost of UHPC are reduced by 41.0%, 33.1%, and 25.9%, respectively, with the addition of 55% CTWP. UHPC with 55% CTWP is a promising whole-life low-carbon concrete.
30. Influence of agricultural fibers size on mechanical and insulating properties of innovative chitosan-based insulators
This work is dealing with the use of miscanthus, recycled textile and rice husks as reinforcement for chitosan matrix to elaborate new insulating composites for building application. Insulating composites having thermal conductivity of 0.07–0.09 W.m−1.K−1 and density of 350–400 Kg.m−3 were manufactured by thermocompression. Different granulometry of miscanthus (0.2–0.5 cm and 1–2 cm) and rice husks (1–2 cm) have been used with and without textile to evaluate the effect of reinforcements particle size and nature on composites thermal and mechanical properties. Thermal conductivity and effusivity shows a linear behavior related to their increasing by raising up the reinforcement’s particle size. The highest mechanical properties in bending (modulus: 69–65 MPa; stress: 0.48–0.45 MPa) and compression (modulus: 36–26 MPa; stress: 0.65–0.56 MPa) were found for the formulations with small size miscanthus. Thus, the incorporation of small miscanthus particle size <1 mm leads to satisfying and promising results in terms of composites competing with the conventional insulating materials used nowadays.
31. Production of autoclaved aerated concrete with silica raw materials of a higher solubility than quartz Part II: Influence of autoclaving temperature
This study examines the effects of autoclaving temperature on the mechanical and microstructural properties of autoclaved aerated concrete (AAC) containing calcined diatomaceous earth (C-DE) as the main silica source. The autoclaving process was conducted using an autoclave at various temperatures of T = 134–192 °C and a corresponding steam pressure of P = 2–12 bar for 6 hours. The resultant phases were characterized using quantitative and qualitative X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The compressive strength of samples containing C-DE as the main silica source increased by 30% when the autoclaving temperature decreased by around 60 °C. This is in complete opposition to samples containing quartz as the only SiO2 source. The compressive strength of the latter decreased by 85% when the autoclaving temperature decreased by approximately 60 °C. For all samples, changes in compressive strength corresponded with changes in tobermorite formation.
32. Structural reinforcement of bi-directional oak-wood lamination by carbon fibre implants
A study of the effect of implants made of carbon fibre reinforced polymer (CFRP) on improving the flexural stiffness of oak-wood model beams laminated in two directions was performed with the goal of improving stiffness in the elastic region, bending strength and overall ductility. Six compositions of implants (resin only, CFRP in various numbers of layers) were introduced in both the tensile and compression zone of the model beams, and some CFRP implants were introduced as pre-tensioned elements. This should enable the modelling of structural elements according to their mechanical requirements depending on the required properties of the final product (construction element, grid member, window, or curtain wall framing, etc.). Displacement and deformations were recorded during four-point bending tests using a 3D video extensometer and were analysed by digital image correlation (DIC). An analysis of the different systems of reinforcements shows that the effective stiffness (EI) and the ultimate load to failure (ULF) can be significantly improved by different types of implants, resulting in an improvement of between 4 and 94% for EI and of 2 and 106% for ULF. Generally, increasing the number of CFRP layers led to an increase in strength and stiffness and a change of ductility of up to 14% which is a sound improvement for the serviceability limit state. A significant reduction in the bending deformation may be obtained by introducing implants, but the effect is not proportional to the number of layers and associated costs. The smallest deformation was obtained on the beam reinforced with 21 layers of CFRP. However, even one or two layers of pre-stressed fibres led to significantly reduced deformations comparable to beams reinforced with multiple carbon layers.
33. Sulfate resistance of self compacting concrete incorporating copper slag as fine aggregates with mineral admixtures
Assessment of copper slag (CS) as fine aggregates on the sulfate resistance of self compacting concrete (SCC) was examined. Three series were prepared and each series contains six mixes. Series 1, series 2 and series 3 were designated as CS mixes, CS mixes blended with silica fume and CS mixes blended with metakaolin respectively. Each series were tested for compressive strength, microstructural analysis and sulfate attack. Mass variation and loss in compressive strength after sulfate exposure were the parameters to assess the sulfate attack. The results reveal that maximum compressive strength exhibited for CS mixes blended with metakaolin followed by CS mixes blended with silica fume. The dense microstructure was observed for series 3 and 2. Among three series, highest change in mass was noticed for CS mixes and lowest for CS mixes blended with metakaolin. Beside rise in the percentage of CS substitution, endurance against sulfate attack enhanced in terms of loss in compressive strength except 100% CS substitution for series 3 and 2 whereas for series 1, resistance to sulfate attack declined beyond 40% CS substitution with reference to control concrete. This study encourages to utilize CS as an alternative to fine aggregates with mineral admixtures for better resistance against concrete structures susceptible to sulfate attack.