《1 Engineering research fronts》

1 Engineering research fronts

《1.1 Development trends in the top 10 engineering research fronts》

1.1 Development trends in the top 10 engineering research fronts

The top 10 engineering research fronts related to the field of civil, hydraulic & architecture engineering are summarized in Table 1.1.1. These fronts cover a variety of disciplines, including structural engineering; construction materials; roads and railway engineering; architecture; heating, ventilation, air conditioning, and gas supplying; municipal engineering; surveying and mapping engineering; and hydraulic engineering. Among these research fronts, “intelligent control systems for building environment,” “migration and transformation mechanisms of microplastics in wastewater treatment,” and “dynamic fusion of geographical spatiotemporal big data for smart cities” are the emerging fronts, while the others are extended from conventional disciplines.

Table 1.1.2 presents the annual statistical data of the core papers published between 2012 and 2017 relevant to the top 10 research fronts. The increasing rate of core papers on intelligent control systems for building environment is the highest among the top 10 research fronts.

(1)   Lifecycle reliability of civil engineering structures and systems

This research front refers to the time-dependent reliability of civil-engineering structures and resulting systems considering the random distribution of loads and the degrading performances of materials, components, and structures during their service life. Under long-term environmental and mechanical loads, structural properties experience stochastic and time-dependent degradation. Based on the theory of stochastic processes, time-dependent structural reliability can be determined through use of probabilistic models of load effects and structural properties. Major issues concerning

《Table 1.1.1》

Table 1.1.1 Top 10 engineering research fronts in civil, hydraulic & architecture engineering

《Table 1.1.2》

Table 1.1.2 Annual number of core papers published for the top 10 engineering research fronts in civil, hydraulic & architecture engineering

this research front include the evolution of structural performance under environmental actions, quantification of the time-dependent reliability index, and reliability of structural systems. Evolution of structural performance has a direct impact on quantification of the reliability index, and introduction of related random variables into the deterministic models of resistance degradation has been widely accepted. The time-dependent reliability index at a component level can be calculated through use of such approaches as the first-passage method, time-independent reliability index for an equivalent series system, Monte Carlo simulation method, and probability-density-evolution method. That said, reliability analysis of systems remains a challenging task. Between 2012 and 2017, 215 core papers have been published relevant to this research front, and these papers have received 4440 citations with an average of 20.65 citations per paper published.

(2)    Ultrahigh-performance and smart cement-based composite materials

Ultrahigh-performance materials refer to composites with superior mechanical properties and durability. Accordingly, smart cement-based composite materials refer to composites with smart functions, such as self-sensing, self-thermal insulation, self-cleaning, and self-damping. With the development of civil engineering structures, the complexity of upgrading structures raises an increasing demand for novel construction materials. Compared with conventional concrete, the ultrahigh-performance concrete (UHPC) demonstrates high compressive strength, excellent toughness, super-high abrasive resistance, antiknock property, and significantly increased durability. The workability and mechanical properties of UHPC have attracted increased research attention in recent years. Owing to the development of carbon-based materials and phase change materials, it is possible to produce smart cement-based composite materials capable of performing intelligent functions, such as self- sensing, self-thermal insulation, and self-cleaning. The use of carbon-based materials, such as carbon nanotubes, graphene, and nano-carbon fiber, improves the mechanical as well as electrical performance of such materials. Upgraded materials can, therefore, ensure safety and reliability of structures and functionalize resulting structures with smart monitoring properties. Between 2012 and 2017, 64 core papers have been published relevant to this research front, and these papers have received 2594 citations in total with an average of 40.53 citations per paper published.

(3)  Highway pavement renewable materials and pavement materials rejuvenation

Concepts of circular economy and sustainable development have drawn increased attention in the field of highway paving, and the use of renewable materials in highway- paving applications and their rejuvenation have become hot topics of research in recent years. Renewable materials are those that follow the principle of bionics and perform dual functions of perception and excitation. Active self- sensing, automatic healing, and self-healing are basic features of such materials. Developing innovative renewable materials, revealing appropriate regeneration mechanisms, and establishing design theories for renewable composite materials are important issues concerning the realization of sustainable development of highway-pavement materials. Material rejuvenation refers to the recycling of industrial and civil wastes, such as steel slags, plastic granules, construction wastes, reclaimed pavement materials, and other materials. Relevant research topics include development of new material recycling technologies, physical and chemical properties of rejuvenated materials, and mechanisms for blending of new and old materials. Between 2012 and 2017, 27 core papers have been published relevant to this research front and have received 601 citations in total with an average of 22.26 citations per paper.

(4)   Green vernacular architecture

Contemporary green vernacular architecture is based on modern building technologies and materials whilst still featuring regional environmental adaptability and cultural continuity. Over the course of its long-term development, vernacular architecture has developed a clear adaptive relationship with its environment. On one hand, such architecture needs to critically absorb the characteristics of climatic adaptation within conventional construction systems while on the other hand, it must respond to requirements of contemporary life and form a sustainable development system that is benign to circumstances and the social environment. Green vernacular architecture not only focuses on the application of technologies concerning modern environmental control, structural safety, culinary and sanitary facilities, and intelligent communication systems to the existing conventional architectural heritage but also devotes itself to discovering the wisdom and experience of vernacular architecture with respect to environmental coordination, climatic adaptation, cultural heritage, and functional organization. Research endeavors in this field pay special attention to the contribution of local architectural forms, construction of national cultural landscapes within environmental adaption, self-adjustment, and self-improvement. Between 2012 and 2017, 317 core papers have been published relevant to this research front and have received 9213 citations with an average of 29.06 citations per paper published.

(5)   AI-based architectural design methodology

The AI-based architectural design methodology considers the architectural design process as its object, artificial intelligence (AI) as its engine, and various virtual reality (VR) technologies as its interface. It brings into full play a combination of the human ability of creating and dealing with uncertainty issues, accurate perception of machines, and high-speed computing ability via intelligent machine systems via real-time interaction. This new concept is superior to conventional ones in three aspects. First, conventional architectural design methodologies are based on monism that sees the architect as the sole subject, whereas the modern approach emphasizes on interaction between human beings and intelligent machines to complete a design, thereby breaking through the monistic mindset of the theoretical framework. Second, the field of AI—with breakthroughs based on the deep neural network technology as its highlight— can recognize and analyze images with accuracies that far exceed human perception and has already outplayed human beings in various game problems through application of enhanced learning algorithms. All these factors enable machines to possess a certain degree of intelligence. Lastly, the light weight and popularization of VR technology in hardware greatly broadens its applications. Compared with the conventional two-dimensional graphical user interface of the screen, its immersive real-time three-dimensional environment greatly enhances the efficiency of information interaction. Simultaneously, with the development of various real-time scanning and projection technologies, the tangible user interface has become popular, got rid of the perception agent mode of both the screen and virtual environment, directly enabled architects to implement various operations with computable information in real objects, and realized direct interactions between humans and machines. Between 2012 and 2017, 107 core papers have been published relevant to this research front and have received 3704 citations with an average of 34.62 citations per paper published.

(6)   Intelligent control systems for building environment

By monitoring the indoor thermal, acoustic, lighting, and air-quality parameters, building intelligent systems (BISs) are primarily used to automatically control and manage mechanical and electrical systems, such as cooling and heating, ventilation, lighting, shading, and façade within residential and corporate buildings, thereby providing, adjusting, and maintaining the desired indoor environment. Presently, major research trends relevant to this front include: ① monitoring and transmission of environmental parameters; ② intelligent analysis, identification, and diagnosis of control systems; and ③ intelligent control and optimization of mechanical and electrical systems. BISs are essentially derived and upgraded from building automation systems, which initially play a supplementary role in monitoring and managing the cooling and heating, elevator, water-supply, security, fire-extinguishing, and power-supply and distribution systems within buildings. Following the rapid development of computers and sensors as well as increasing popularization of intelligent terminals (e.g., smartphones, smart wearable devices, and display screens), BIS offers more possibilities and opportunities for providing an appropriate, customizable, and comfortable indoor environment. For example, the subjective perception of an indoor environment by occupants can be first collected via intelligent terminals and subsequently used as input to BIS to integrate personalized preferences with regard to indoor temperature, humidity, airflow, lighting, etc. Between 2012 and 2017, 31 core papers have been published relevant to this research front and have received 1244 citations with an average of 40.13 citations per paper published.

(7)   Migration and transformation mechanisms of microplastics in wastewater treatment

Microplastics correspond to plastic particles and textile fibers with tiny particle sizes. These are generally considered plastic particles measuring less than 5 mm in dimension. The primary source of these particles is plastics, which are widely used in daily life, and after being exposed to the natural environment, gradually reduce in size owing to the effect of the wind and sun. Additionally, there exists a large quantity of frosted particles in cosmetics or cleansing products in addition to the large number of fibers contained in the wastewater discharged from household washing machines. These microplastics possess small volumes, large specific surface areas, and a strong ability to adsorb pollutants. They are, therefore, likely to form organically contaminated spheres with persistent organic pollutants, such as hydrophobic polychlorinated biphenyls and bisphenol A. Microplastics cannot be effectively removed in conventional urban wastewater treatment plants because they tend to float on the water surface during treatment. Wandering microplastics can easily be swallowed by such organisms belonging to the lower end of the food chain as mussels and zooplanktons. These plastics, however, cannot be digested, thereby causing disease and mortality in such organisms. If microplastics containing organic contaminants are eaten, the contaminants tend to be released—under the action of enzymes—within the organisms’ bodies, thereby exacerbating their damaging impacts. If the said microplastics and organic pollutants enter bodies of organisms belonging to the upper part of the food chain, the “enrichment” effect of the food chain can cause widespread mortality of a larger organism community. Researches concerning mechanisms of migration and transformation of microplastics relevant to sewage treatment focus on determination of ① the composition of microplastics present within sewage via use of various approaches—observations, experiments, theoretical models, and numerical simulations; and ② migration pathways, conversion products, transformation, and distribution of microplastics and other pollutants within sewage-treatment systems using various techniques. The said researches target elimination of microplastics, persistent organic pollutants, heavy metals, endocrine disruptors, emerging pollutants, etc. Between 2012 and 2017, 7 core papers have been published relevant to this research front and have received 243 citations with an average of 34.71 citations per paper published.

(8)     Fusion and processing of multilevel space-air-ground remote-sensing data

Fusion and processing of multilevel space-air-ground remote- sensing data refers to a deep fusion of remote-sensing big data, including multisource and multilevel aerospace and ground remote-sensing data, to analyze image features and discover inherent regularities between multisource data based on physical characteristics of ground objects. Using the hybrid multi-level fusion technology, desired information can be extracted by combining the pixel, feature, and decision- making layers and integrating professionally constructed models. Major issues encountered in this research front include ① high-precision preprocessing of multisource remote-sensing data, including radiometric calibration, geometric correction, atmospheric correction, and co-accurate correction of multisource heterogeneous data; ② spatial fusion of multisource remote-sensing data, major methods of which include combined block adjustment and image registration; the former method converts a spatial fusion problem into a joint block-adjustment problem involving multisource remote-sensing data from the perspective of photogrammetry, whereas the latter converts a spatial fusion problem into an image registration problem from the perspective of image processing and computer vision; and ③ the informational fusion of spatially fused multisource remote-sensing data to extract new and meaningful information. The process of informational fusion can, in general, be divided into three levels—pixel level, feature level, and decision level. Development trends in this research front include ① support of combined block adjustment of multisource data to enable automatic search and joint adjustment of corresponding points among various sources, phases, and resolutions; ② in-depth informational fusion based on multilayer blending; and ③ information extraction based on deep learning and neural networks. Between 2012 and 2017, 141 core papers have been published relevant to this research front and have received 7023 citations with an average of 49.81 citations per paper.

(9)    Dynamic fusion of geographical spatiotemporal big data for smart cities

With the construction of smart cities, numerous widespread sensors generate PB, EB, or even ZB levels of urban geographical spatiotemporal datasets. Dynamic fusion of geographical spatiotemporal big data of a smart city aims at automatically discovering and extracting implicit and non-obvious patterns, rules, and knowledge from real- time, multiplatform, multitemporal, multisensor, multitype, high-resolution, hyper-spectral, and massive multisource geographical spatiotemporal big data followed by a quick transformation of geographical spatiotemporal big data to valuable information via efficient, intelligent, and dynamic processing. The proposed fusion process, is believed, would greatly improve the spatial cognition ability of smart cities. Major issues concerning this research front include basic theories and methods for representation, measurement, and understanding of geographical spatiotemporal big data of smart cities along with revelation of relationships between spatiotemporal big data and real objects, behaviors, and events. Worldwide research endeavors being undertaken relevant to this topic have resulted in multidisciplinary studies being performed for collecting geospatial and temporal data of physical objects and human activities within smart cities via various methods and integrated approaches, information extraction, network management, knowledge mining, spatial knowledge perception, and provision of intelligent location services. Between 2012 and 2017, 52 core papers have been published relevant to this research front and have received 1244 citations with an average of 23.92 citations per paper.

(10)   Lifecycle safety of water-related engineering

Water-related engineering is a key component of infrastructure systems and plays an irreplaceable role in ensuring water safety as well as social and economic development. In recent years, water-related construction activities have expanded from inland regions into the deep sea, and higher safety requirements are being specified to be met during deep-sea construction and operation with the working environment becoming more complex and diverse within deep water. Lifecycle safety of water-related engineering is a concept raised in view of security threats and changes in surrounding environments encountered during all stages of a structure's service life. Major research endeavors in this regard are concerned with ① development of anti-vibration, anti-corrosion, and anti-seismic technologies for water-related engineering structures; ② nondestructive detection, damage identification, and rapid repair technologies for underwater structures; ③ diagnostic evaluation of safety of water-related structures; and ④ optimization of lifecycle safety design of water projects. Compared to hydraulic structures, port structures, and offshore engineering, deep-sea engineering operations are confronted with more complex environmental factors, including both normal (e.g., wind, wave, current, and salinity) and extreme factors (e.g., typhoons and earthquakes). In order to ensure the safety of deep-sea engineering operations, the combined action of various environmental factors must be taken into consideration. Response and failure mechanisms of deep-sea engineering structures under complex environments could be analyzed via experiments as well as numerical simulations, on the basis of which lifecycle performance monitoring and damage repair systems could be established. This would ultimately lead to satisfaction of lifecycle safety assessment and design criteria concerning deep-sea operations. Consequently, researches concerning catastrophic mechanisms, intelligent monitoring, and automatic repair technologies under complex conditions, lifecycle safety evaluations, and optimization design of the structural system will remain the major focus in this research front. Between 2012 and 2017, 49 core papers have been published relevant to this research front and have received 913 citations with an average of 18.63 citations per paper.

《1.2 Interpretations for three key engineering research fronts》

1.2 Interpretations for three key engineering research fronts

1.2.1 Lifecycle reliability of civil engineering structures and systems

Owing to rapid industrialization, large-scale infrastructure constructions have been undertaken in many countries since the middle of the twentieth century. Meanwhile, the durability and service life of civil-engineering structures have become topics of concern for the entire society. Certain structures tend to degrade prematurely owing to insufficient knowledge concerning the evolution of structural performance. Structural engineers have, over the years, realized the significance of the service life of structures and proposed a series of design methods, including the allowable stress, ultimate strength, and limit state design methods, all relating to the service life of structures. Presently, the limit-state design method, based on the probability theory, has been examined and adopted in several engineering practices. This approach, however, considers a structure to demonstrate a state of construction completion with loads varying over the target service life whilst ignoring performance degradation of the structure itself over a period of time.

In an attempt to determine more appropriate approaches, researchers proposed stochastic-process-based reliability- analysis methods by introducing time-dependent probabilistic models for degradation resistance of structures. However, there continues to exist the lack of an in-depth understanding of performance evolution of various structures subjected to environmental and mechanical loads. This is because the available models often provide results largely deviating from observations in actual scenarios. Based on the different resistance degradation models, time-dependent reliability- analysis techniques have been proposed, such as the first- passage method, time-dependent reliability of an equivalent series system, and Monte Carlo simulation. The first two methods are either inapplicable to time-dependent reliability- index calculation or limited to specific stochastic physical systems. The Monte Carlo simulation method is relatively time-consuming, although it has been widely employed with high accuracy without being limited to stochastic physical systems and limit state equations.

Currently, major topics of research concerning the lifecycle reliability of civil engineering structures and systems include

(1)  Improved methods for time-dependent reliability analysis. Examples under this topic include the Poisson-process-based analytical and Monte-Carlo-simulation-based stochastic methods, both of which have been proposed to reduce the high computational cost associated with the direct simulation method and resolve the difficulty in sampling events with a small probability. Additionally, the probability density evolution method—based on the principle of probability conservation—has been extended to applications involving time-dependent reliability analysis.

(2)  Improved time-dependent state functions of structures and systems. Related studies include a) assessment of the reliability of reinforced concrete (RC) structures considering time-dependent corrosion rate of steel bars and spatially varying distribution of corrosion current density and corrosion morphology; and b) establishment of equivalent extreme events and performing associated reliability analysis considering complex structural failure modes.

(3)  Design and maintenance of structures and systems based on time-dependent reliability.

As listed in Table 1.1.1, 215 core papers have been published between 2012 and 2017 concerning "lifecycle reliability of civil engineering structures and systems," and each paper has been cited an average of 20.65 times. The top 3 nations in terms of core-paper output in this regard are China, USA, and Italy (Table 1.2.1). China is one of the most active players in this topic, publishing 33.49% of core papers and ranking first in terms of quantity. In terms of core-paper citation, papers published by the Chinese have each been cited 21.15 times on average, slightly exceeding the corresponding global average number. This indicates that researchers from China are gradually gaining more attention. As illustrated by the international collaborative network depicted in Figure 1.2.1, close cooperation has been observed among the most productive top 10 countries/regions except Czech Republic.

As listed in Table 1.2.2, the top 3 institutions publishing the most number of core papers are Hunan University (China), Dalian University of Technology (China), and Tongji University (China). As illustrated in Figure 1.2.2, collaborative studies are rare among the top 10 most productive institutions in this regard.

As listed in Table 1.2.3, the top 3 most productive countries/ regions (i.e., China, USA, and Italy) are also the most active ones in terms of the most number of citing papers between 2012 and 2017. Note that approximately 40% citations of core papers are contributed by China, thereby indicating that Chinese researchers pay increased attention to researches performed concerning this front. As presented in Table 1.2.4, the top 3 institutions citing the most number of core papers are Hunan University (China), Tongji University (China), and Lehigh University (USA).

Summarizing the above statistical data, it can be stated that China is, at present, the leading player in terms of research trends concerning “lifecycle reliability of civil engineering structures and systems.” As such, continuous support at the national and provincial levels is important for sustaining dedicated studies to maintain China’s leading position concerning this topic.

《Table 1.2.1》

Table 1.2.1 Countries or regions with the greatest output of core papers on the “lifecycle reliability of civil engineering structures and systems”

《Table 1.2.2》

Table 1.2.2 Institutions with the greatest output of core papers on the “lifecycle reliability of civil engineering structures and systems”

《Figure 1.2.1》

Figure 1.2.1 Collaborative network among major countries or regions in the engineering research front of “lifecycle reliability of civil engineering structures and systems”

《Figure 1.2.2》

Figure 1.2.2 Collaborative network among institutions in the engineering research front of “lifecycle reliability of civil engineering structures and systems”

《Table 1.2.3》

Table 1.2.3 Countries or regions with the greatest output of citing papers on the “lifecycle reliability of civil engineering structures and systems”

《Table 1.2.4》

Table 1.2.4 Institutions with the greatest output of citing papers on the “lifecycle reliability of civil engineering structures and systems”

1.2.2 Ultrahigh-performance and smart cement-based composite materials

With the advancement in social economy, structural design theory, and construction technology, engineering structures have grown higher, longer, and deeper in recent years. To enable construction of complicated engineering structures, there exists an increasing demand for development of non- conventional construction materials, such as ultrahigh- performance composite (UHPC) materials with superior mechanical properties, toughness, abrasive resistance, antiknock property, and durability. Meanwhile, there also exists a need for structures capable of performing delicate and intelligent functions to meet the objective of realizing reliable and safe living and traffic conditions. The smart cement-based composite material is one such material capable of demonstrating the said intelligent functions. It has great potential for use in the monitoring stress, strain, and temperature within important structural components. It could serve as a useful nondestructive tool to estimate structural damage as well as to achieve timely recovery of such damages. Moreover, this smart material can also be specially functionalized to relieve impacts from typhoons and earthquakes as well as manipulate temperature, humidity, and energy consumption within indoor environments. As a highly technical material, the use of smart cement-based composite has opened new avenues with regard to future development of conventional construction materials as well as new research opportunities. Further studies concerning basic theories and applications are required to realize breakthrough development concerning novel structural materials, which in turn, would help researchers create a huge market with great social and economic benefits.

Major research topics concerning ultrahigh-performance and smart cement-based composite materials include the following.

(1)   Preparation technology and performance control of UHPC. This topic mainly covers two aspects, the first of which concerns determination of UHPC characteristics whilst focusing on the rheology and pumping ability of UHPC and aims at its successful applications in complex high, long, and deep structures. The second aspect relates to investigations concerning macroscopic mechanical properties and durability of UHPC as well as the relationship between UHPC microstructures and said macroscopic properties.

(2)  Engineering applications of UHPC. In addition to ensuring its own performance requirements, UHPC applications in engineering structures require a comprehensive study concerning mechanical properties of various structural members made of this material. Such studies are potentially useful in the establishment of mature reliability design calculation methodologies. There, however, exist many challenges with regard to extensive applications of this material to engineering structures, such as buildings, bridges, roadbeds, and dams.

(3)   Intelligent monitoring characteristics of smart cement- based composite materials. An important area of research concerning smart cement-based composite materials is to functionalize conventional cement-based materials with self- monitoring and self-diagnosis abilities. More attention is paid to the self-monitoring ability of structures with regard to stress, deformation, and temperature monitoring. Against a background of rapid development of carbon-based materials, such as carbon fiber, carbon nanotubes, and graphene, improving the sensitivity, stability, application range, and durability of smart cement-based materials holds great potential.

(4)   Intelligent adjustment characteristics of smart cement- based composite materials. Another intelligent direction of smart cement-based composites is self-regulation and self- healing abilities. These materials adapt to changes in the service environment as well as their own structures, such as self-adjustment to temperature and humidity, self-control of shape and damping, and self-healing of microcracks. Researches performed in this direction have a broad future market.

As listed in Table 1.1.1, 64 core papers have been published between 2012 and 2017 concerning “ultrahigh-performance and smart cement-based composite materials,” and each paper has been cited 40.53 times on average. The top 3 countries in terms of core paper output are the USA, South Korea, and China (Table 1.2.5). China is one of the most active players in this context, producing 17.19% of the core papers. In terms of core-paper citations, papers published by China have each been cited 42.45 times on average, slightly exceeding the global average number. This indicates that researchers from China are gradually gaining increased attention. As illustrated by the international collaborative network depicted in

Figure 1.2.3, a relatively close cooperation is noted among China, USA, and UK.

As listed in Table 1.2.6, the top 3 institutions publishing the most number of core papers are Korea University (South Korea), the University of Michigan (USA), and the University of Connecticut (USA). As illustrated in Figure 1.2.4, domestic cross-organization collaborations are frequent in USA and South Korea, whereas crossover collaborations between different countries are rare.

As listed in Table 1.2.7, the top 5 countries/regions citing the most core papers are China, USA, South Korea, Australia, and Italy. Note that 31.45% citations of core papers have been contributed by China, indicating that Chinese researchers pay close attention to researches performed in this regard. As presented in Table 1.2.8, the top 3 institutions citing the most core papers are Korea University (South Korea), Harbin Institute of Technology (China), and Hanyang University (South Korea).

Summarizing the above statistical data, China is currently among leading players with regard to research endeavors concerning "ultrahigh-performance and smart cement-based composite materials." Enhanced support at national and provincial levels is, therefore, significant in promoting China’s contribution towards creating greater awareness concerning the topic.

《Table 1.2.5》

Table 1.2.5 Countries or regions with the greatest output of core papers on the “ultrahigh-performance and smart cement-based composite materials”

《Table 1.2.6》

Table 1.2.6 Institutions with the greatest output of core papers on the “ultrahigh-performance and smart cement-based composite materials”

《Figure 1.2.3》

Figure 1.2.3 Collaborative network among major countries or regions in the engineering research front of “ultrahigh-performance and smart cement-based composite materials”

《Figure 1.2.4》

Figure 1.2.4 Collaborative network among major institutions in  the engineering research front of “ultrahigh-performance and smart cement-based composite materials”

《Table 1.2.7》

Table 1.2.7 Countries or regions with the greatest output of citing papers on the “ultrahigh-performance and smart cement-based composite materials”

《Table 1.2.8》

Table 1.2.8 Institutions with the greatest output of citing papers on the “ultrahigh-performance and smart cement-based composite materials”

1.2.3 Highway pavement renewable materials and pavement materials rejuvenation

Concepts of circular economy and sustainable development have drawn increased attention in the field of highway paving. Renewable materials in highway-paving applications and pavement materials rejuvenation have become hot topics of research in recent years. Renewable materials are those that follow the principle of bionics and perform dual functions of perception and excitation. Active self-sensing, automatic healing, and self-healing are basic features of such materials. Developing innovative renewable materials, revealing appropriate regeneration mechanisms, and establishing design theories for renewable composite materials are important issues concerning the realization of sustainable development of highway-pavement materials. Material rejuvenation refers to the recycling of industrial and civil wastes, such as steel slags, plastic granules, construction wastes, reclaimed pavement materials, and other materials. Relevant research topics include development of new material recycling technologies, physical and chemical properties of rejuvenated materials, and mechanisms for blending of new and old materials.

Researches concerning use of recycled materials for pavements mainly focus on the application of self-healing materials. Currently available self-healing materials can repair millimeter-scale cracks, but self-repair of wide and deep cracks requires theoretical innovations and development of related technologies. Some smart materials, such as self-aware materials and shape memory polymers, have been successfully employed in aerospace and other niche applications. Although these materials have found applications in the highway- pavement industry within Europe and USA, the overall technology is still in its infancy. Researches concerning material regeneration primarily focus on sustainable utilization of solid wastes in highway pavement engineering, but the blending mechanism of the regeneration process is unclear, thereby resulting in degrading road performance. It is, therefore, necessary to further investigate scientific issues concerning renewable materials and materials rejuvenation.

Sustainable development of global transportation infrastructure promotes research endeavors concerning highway pavement whilst focusing on both renewable materials and materials rejuvenation. Owing to the self- repairing and shape-memory functions of new recycled materials, realization of effective improvement in pavement performance, prolonged pavement life, reduction in pavement maintenance costs can now be made possible. Material regeneration can effectively alleviate problems concerning global resource shortage and environmental pollution. Researches concerning highway pavement through use of renewable materials and their regeneration are, therefore, conducive to the improvement of technology and the economy as well as environmental protection, which is in accordance with the objective of sustainable development.

Major areas of the research concerning “highway pavement renewable materials and pavement materials rejuvenation” include the following.

(1)   Revelation of physicochemical properties, intelligent perception, and self-repair mechanism of renewable materials; development of new renewable highway pavement materials; establishment of synergistic models of composite renewable materials; analysis of the synergistic mechanism between regenerated and original materials; development of intelligent and adaptive renewable materials; and performance optimization of renewable materials under multi-physics coupling conditions.

(2)  Revelation of long-term cooperative working mechanism of various components of material regeneration, such as the synergy between new and old asphalt mixtures, synergy between external components and original materials, and synergistic effect of various components of new cement-based materials; establishment of industrial and civil waste materials gene database; exploration of advantages and defects of waste materials; and application of material calculation design theory to facilitate realization of green, refined, and efficient material regeneration processes.

As listed in Table 1.1.1, 27 core papers were published between 2012 and 2017 concerning "highway pavement renewable materials and pavement materials rejuvenation", and each paper was cited 22.26 times on average. The top 5 countries in terms of core-paper publishing are Spain, Australia, USA, Italy, and Portugal (Table 1.2.9). The top 5 countries/ regions receiving the highest citations are Sweden, USA, Canada, Spain, and Switzerland. International collaboration is not very common among the most productive countries/ regions with regard to this research front, as illustrated in Figure 1.2.5.

As listed in Table 1.2.10, the University of Córdoba (Spain) has published the most number of core papers. As illustrated in Figure 1.2.6, collaborative studies are rare among the top 10 most productive institutions.

As indicated in Table 1.2.11, the top 5 countries/regions citing the most number of core papers include China, USA, Spain, Australia, and UK. It can, therefore, be inferred that Chinese researchers pay keen attention to researches performed in this field. As presented in Table 1.2.12, the top 3 institutions citing the most number of core papers are the Swinburne University of Technology (Australia), University of Córdoba (Spain), and University of Nottingham (UK).

Summarizing the above statistical data, it can be said that China is catching up and paying keen attention to researches concerning “highway pavement renewable materials and pavement material rejuvenation,” and that enhanced support at the national and provincial levels is important for promoting China’s contribution to this topic.

《2 Engineering development fronts》

2 Engineering development fronts

《2.1 Development trends in the top 10 engineering development fronts》

2.1 Development trends in the top 10 engineering development fronts

Top 10 engineering development fronts in the field of civil,

《Table 1.2.9》

Table 1.2.9 Countries or regions with the greatest output of core papers on the “highway pavement renewable materials and pavement materials rejuvenation”

《Table 1.2.10》

Table 1.2.10 Institutions with the greatest output of core papers on the “highway pavement renewable materials and pavement materials rejuvenation”

《Figure 1.2.5》

Figure 1.2.5 Collaborative network among major countries or regions in the engineering research front of “highway pavement renewable materials and pavement materials rejuvenation”

《Figure 1.2.6》

Figure 1.2.6 Collaborative network among major institutions in  the engineering research front of “highway pavement renewable materials and pavement materials rejuvenation”

《Table 1.2.11》

Table 1.2.11 Countries or regions with the greatest output of citing papers on the “highway pavement renewable materials and pavement materials rejuvenation”

《Table 1.2.12》

Table 1.2.12 Institutions with the greatest output of citing papers on the “highway pavement renewable materials and pavement materials rejuvenation”

hydraulic & architecture engineering are summarized in Table 2.1.1. These fronts cover a variety of disciplines, including structural engineering, urban and rural planning and landscape, roads and railway engineering, geotechnical and underground engineering, bridge engineering, construction materials, municipal engineering, hydraulic engineering, and surveying and mapping engineering. Among these development fronts, "intelligent construction and 3D printing technology," "green planning and building technology" and "collaborative development and utilization of urban underground space" are emerging fronts, whereas other fronts have been extended from conventional subjects. Table 2.1.2 presents annual statistical data of core patents published between 2012 and 2017 concerning the top 10 development fronts.

(1)  Intelligent construction and 3D printing technology

Intelligent construction refers to use of a cyber-physical system (CPS) with advanced construction technologies deeply integrated with information technology. Developed from industrial construction and digital construction systems, intelligent construction comprises a combination

《Table 2.1.1》

Table 2.1.1 Top 10 engineering development fronts in civil, hydraulic & architecture engineering

《Table 2.1.2》

Table 2.1.2 Annual number of core patents published for the top 10 engineering development fonts in civil, hydraulic & architecture engineering