Editorial: Special Issue on Smart and Green Infrastructures with Optimum Life Cycle Solutions
Authors: Liu Yong , Chen Dar Hao 
Published: October 2022

Abstract
There are successful projects in many different countries using green infrastructure approaches to reduce imperviousness and preserve natural open space throughout a watershed and at the neighborhood scale, as well as adding green infrastructure practices at the site level. Intensive development of structures and the necessary supporting infrastructure is ongoing throughout the world. Although most of the urban areas are already densely settled with buildings above and below the ground, there is still a pressing need to construct new structures between or beneath the existing ones. In addition, topics such as recycling and warm mix asphalts are of interest for this special issue. This special issue on Smart and Green Infrastructures with Optimum Life Cycle Solutions in ASTM International’s Journal of Testing and Evaluation contains 27 papers. All papers in this special issue can provide a repository of the state-of-the-art research outcomes and state-of-the-practice case studies on smart and green infrastructures with optimum life cycle solutions. A wide range of topics are covered in this special issue, which advances the domain of smart and green infrastructures. The research topics in the issue include soil and rock, asphalt mixtures, asphalt mixtures, and fly ash as well as the innovative technologies for the application of novel materials in earthworks, accelerated infrastructure construction, and improvement of decision-making performance for infrastructures. This special issue offers a platform for sharing the latest results on the resiliency and green technologies of civil infrastructures. Typical topics include investigations related to civil infrastructures such as road construction, drainage system, tunnel project, and high fill slope. In addition, a number of civil and transportation materials related to geotechnical aspects of infrastructure are scientifically examined. This information should lead to more resilient infrastructure design, maintenance, and management. The rapid construction of urban infrastructure and transportation engineering facilitates the demand for green building materials and geotechnical materials. There are 11 papers involving building materials and geotechnical materials–related topics, including Gobi gravel soils (GGS), roller compacted concrete (RCC), fly ash, Montmorillonite Indian clay, and frozen soils. Among them, some novel materials have been testified and their engineering characteristics have been explored in four papers. Chen et al. studied the unconfined compressive strength of soils stabilized via gypsum-slag curing agent and cement. The authors developed the relationship between apparent porosity and unconfined compressive strength based on Python image processing method and concluded that the presence of the gypsum-slag hardening agent changes the microstructure and increases the unconfined compressive strength of the original soils. Wu and Li evaluated a novel high-performance solidified soil material from various perspectives including mechanical, water resistance, and antifrost performance. The authors noted that the 7 days unconfined compressive strength of this novel material had been enhanced by about 2 to 3 times compared with that of cement-stabilized aggregates. The results can offer some suggestions for the construction of a low-grade highway. The work of Le et al. focuses on the possibility of utilizing locally available soil in a lightweight foamed concrete mixture as an alternative sustainable solution. The authors observed that air foam content noticeably improves the self-leveling of backfill material, and it should be added lower than 20 % in order to ensure sufficient strength gain. To accurately quantify unfrozen water content in frozen soils, Ren et al. adopted the frequency domain reflectometry technique to measure the unfrozen water content of the prepared soil specimens. It was claimed that neither of the freeze-thaw cycles nor the freezing or thawing methods had significant impact on the measured soil-freezing characteristic curve. Regarding the improvement of concrete material performance, Au and Nam assessed the in situ and full-scale performance of recycled concrete aggregate (RCA), which is utilized as a pipe bedding and backfill material. Their research was based on both laboratory and field experiments and explored the exfiltration subdrainage performance of each RCA French drainage system. They demonstrated that RCA could be utilized as a subdrainage material and avoided a significant reduction in drainage system exfiltration performance compared with traditional materials (limestone). The work of Yao et al. extensively investigates the essential factors affecting pressure bleeding rate for high-strength concrete with good fluidity. Moreover, they suggested that some bleeding improvement measures and an appropriate mix ratio can obtain better performance for high-strength concrete. The work of Zhong et al. provides a comprehensive knowledge of the optimum workability of RCC. The authors reported the Vebe consistency decreased with the increase of the water-cement ratio. Furthermore, they found the optimal range of cement slurry surplus parameter was about 1.1 to 1.4 and the optimal range of cement mortar surplus parameter was about 1.2 to 1.6. An optimal sand ratio was also given, which had a prominent impact on RCC. To improve the engineering characteristics of expansive soil, Singh et al. utilized scanning electron microscope (SEM) and X-ray diffraction to study the mineralogical characteristics for both natural samples and reconstituted samples and investigated the different proportions of fly ash affecting the deformation behavior of expansive Montmorillonite Indian clay. Syed et al. used alkali-activated binder to enhance the subgrade strength characteristics of the expansive soil, and four types of fibers (polypropylene, glass, hemp, and coir fiber) are also selected to reinforce the expansive soil. Besides, the authors established a nonlinear regression model to predict the subgrade strength failure based on Monte Carlo simulation. They reported that the optimum dosages of fiber reinforcement and slag (or fly ash) are key factors for regulating the volumetric instability and tensile cracks of expansive soil. Lou et al. surveyed another modifier, superhydrophobic nano-SiO2, to improve the geotechnical characteristics of expansive soil. According to their laboratory test results, the optimum superhydrophobic nano-SiO2 content was 0.6 %. The study of Cai et al. focuses on improving the performance of impermeable bentonite to meet the requirements of low permeability, high chemical resistance, and strong adsorption performance. The authors explored the morphological changes and microstructure of raw bentonite and sodium polyacrylate (SPB) with various Cu2+ concentrations via SEM. They mentioned that the SPB could enhance the antiseepage ability and chemical resistance of bentonite as well as improve the adsorption of heavy metals. Topics related to recent developments in geotechnical engineering are discussed in three papers. Two are related to slope engineering stability, and the other one is related to underground construction. Wan et al. conducted a series of large-scale triaxial tests on GGS to investigate the influencing factors on its mechanical behavior, including coarse content, degree of compaction, and confining pressure. The authors evaluated the effects of slope angle and geotextiles on the safety factor. They also suggested the optimal value of slope angle and the optimum geotextiles reinforcement. The research of Xin et al. aims to study the characteristics and distribution of geological hazards along the pipeline. The authors conducted a case study on the basis of pipeline landslide hazard monitoring and data analysis technologies. They concluded that rainfall may cause concentrated stress and deformation of the pipeline, thereby causing a landslide. In a separate study, Jiang et al. performed a correlation analysis of rock mass properties and tunnel boring machine (TBM) parameters on the basis of the field data obtained from the Yin-song headrace tunnel in China. The authors built a statistical prediction model to perform the prediction of penetration rate through multivariate linear regression analysis, which can provide some constructive suggestions on the low life cycle cost of a TBM. Maintenance, rehabilitation, structural health, life cycle management, remediation techniques, safety assessment, and pavement management decision-making are other areas covered in this special issue and are discussed in five research articles. Chen et al. analyzed pavement maintenance and rehabilitation (M&R) activities by introducing belief function theory, which proposed a precise and straightforward method to assist engineers in conducting M&R decision-making. The research of Steyn and Broekman proposed a novel framework based on Digital Twins technology. By integrating the environmental monitoring, physical, surface temperature, and management data, the authors provide references for assisting the maintenance of roads. Qiu et al. established a numerical model of a typical subgrade structure under the action of a snowdrift by including in the scope of the influence of a typical roadbed structure. The authors conducted numerical simulations by computational fluid dynamics method to testify the influence of the motion characteristics of snow particles on the flow field. Yuan et al. gave a new perspective to monitor the structural health of infrastructure through introducing the digital zenith tube, which was evolved on the basis of the astrogeodetic and photogrammetric theory. Omar et al. evaluated the influence of the in situ precontamination moisture content on the performance of fine-grained soil contaminated with various levels of used engine oil. The authors reported that knowledge of site moisture levels before contamination is vital to assess the influence of contamination by the engine oil. Eight papers in this special issue are related to the design life, resilient modulus measurement, pavement construction, subbase, and bridges. The work by Zhong et al. studies the design methods for the mix ratio of RCC during the construction process of the Qinglian highway rehabilitation project. In order to find out the optimal value of the mix ratio, the orthogonal test method was adopted. An optimal amount of cement was given by the authors, which can reduce the occurrence of road distresses on the premise of meeting the strength requirements. These results may combine the practical project with a mixture ratio design and use the indicators recommended in the design process. The work of Yang focuses on the correction of piston friction before conducting a resilient modulus test by utilizing an external load cell. The author assessed the effects of piston friction on the resilient modulus of residual lateritic soils compacted at optimum moisture content and built the correction procedures based on test findings. Lai et al. emphasized bridging the gap between the difference in laboratory and field compaction and developing a quick and economical method for the quality control of backfills. They designed a rotary compactor and a miniature dynamic cone penetrometer to compact the soil samples with different water contents. The study by Tapase et al. works on the perfection of the analysis and design process for flexible pavement by considering a variety of materials to be used in different layers of pavement. The authors demonstrated the method by depicting the design charts under the consideration of comprehensive factors with various natures, which may exhibit a more ecofriendly and economic framework. Focusing on dealing with the rutting of asphalt pavement, Zhang et al. explored a new antirutting asphalt mixture that contains seven different materials. In addition, the authors demonstrated that the Chinese rutting test was more suitable for high-modulus asphalt mixture, and improving the high temperature stability of the asphalt mixture can slow down the attenuation of the antishipping property. Huang et al. designed and molded four types of asphalt mortar specimens with different aggregates to investigate the influence of limestone, basalt, diabase, and steel slag on the road performance of asphalt mortar. They noted that basalt asphalt mortar exhibited the best comprehensive pavement performance. The work by Ashfaq et al. focuses on assessing the unconfined compressive strength characteristics of lime and gypsum-treated coal gangue. The authors utilized target reliability-based design optimization to assess the optimal amounts of lime and gypsum content for the satisfactory performance of pavements. Moreover, for accelerated bridge construction, the study of Xiang et al. focuses on the varyingly grout aged specimens and performed laboratory tests to analyze the interior failure modes of specimens by industrial computed tomography detecting technology. The authors proposed a numerical model related to grout age and the stress-slip. Last but not least, we would like to sincerely thank the reviewers for their thoughtful comments and efforts toward improving the scientific quality of articles in this special issue. This special issue is expected to play an essential role in advancing the boundary of geotechnical engineering, which can support decisions regarding the optimal management and maintenance of civil infrastructures to provide a smarter and greener life cycle solution for geotechnical engineering practitioners.