Bird’s-eye view of recycled solid wastes in road engineering

Recent trends in road engineering have explored the potential of incorporating recycled solid wastes into infrastructures that including pavements,bridges,tunnels,and accessory structures.The utilization of solid wastes is expected to offer sustainable solutions to waste recycling while enhancing the performance of roads.This review provides an extensive analysis of the recycling of three main types of solid wastes for road engineering purposes:industrial solid waste,infrastructure solid waste,and municipal life solid waste.Industrial solid wastes suitable for road engineering generally include coal gangue,fly ash,blast furnace slag,silica fume,and steel slag,etc.Infrastructure solid wastes recycled in road engineering primarily consist of construction&demolition waste,reclaimed asphalt pavements,and recycled cement concrete.Furthermore,recent exploration has extended to the utilization of municipal life solid wastes,such as incinerated bottom ash,glass waste,electronics waste,plastic waste,and rubber waste in road engineering applications.These recycled solid wastes are categorized into solid waste aggregates,solid waste cements,and solid waste fillers,each playing distinct roles in road infrastructure.Roles of solid waste acting aggregates,cements,and fillers in road infrastructures were fully investigated,including their pozzolanic properties,integration effects to virgin materials,modification or enhancement solutions,engineering performances.Utilization of these materials not only addresses the challenge of waste management but also offers environmental benefits aiming carbon neutral and contributes to sustainable infrastructure development.However,challenges such as variability in material properties,environmental impact mitigation,secondary pollution to environment by leaching,and concerns regarding long-term performance need to be further addressed.Despite these challenges,the recycled solid wastes hold immense potential in revolutionizing road construction practices and fostering environmental stewardship.This review delves into a bird’seye view of the utilization of recycled solid wastes in road engineering,highlighting advances,benefits,challenges,and future prospects.

Preparation and Characterization of High-Strength Geopolymer Based on BH-1 Lunar Soil Simulant with Low Alkali Content

The construction of a lunar base and habitation on the Moon has always been on researchers’minds.Building materials used in in situ lunar resources are of great significance for saving expensive space freight.In this study,a new type of lunar soil simulant named Beihang(BH)-1 was developed.The chemical mineral composition and microstructure of BH-1 closely resemble those of real lunar soil,as verified by X-ray fluorescence spectroscopy(XRF),X-ray diffraction(XRD),scanning electron microscopy(SEM),and reflectance spectra.This research also synthesized a geopolymer based on BH-1 cured at simulated lunar atmospheric conditions.We also investigated the effect of supplementing aluminum(Al)sources on the enhancement of geopolymer strength based on BH-1.The rheological behavior of alkali-activated BH-1 pastes was determined for workability.XRF,XRD,Fourier transform infrared spectroscopy,SEM coupled with energy dispersive spectroscopy,and 27Al magic angle spinningnuclear magnetic resonance were used to characterize resulting geopolymers.Rheological test findings showed that the rheology of BH-1 pastes fits the Herschel–Bulkley model,and they behaved like a shear-thinning fluid.The results showed that the 28-day compressive strength of the BH-1 geopolymer was improved by up to 100.8%.Meanwhile,the weight of additives required to produce per unit strength decreased,significantly reducing the mass of materials transported from the Earth for the construction of lunar infrastructure and saving space transportation costs.Microscopic analyses showed that the mechanism to improve the mechanical properties of the BH-1 geopolymer by adding an additional Al source enhances the replacement of silicon atoms by Al atoms in the silicon–oxygen group and generates a more complete and dense amorphous gel structure.

Smoothed particle hydrodynamics based numerical study of hydroplaning considering permeability characteristics of runway surface

The presence of water films on a runway surface presents a risk to the landing of aircraft.The tire of the aircraft is separated from the runway due to a hydrodynamic force exerted through the water film,a phenomenon called hydroplaning.Although a lot of numerical investigations into hydroplaning have been conducted,only a few have considered the impact of the runway permeability.Hence,computational problems,such as excessive distortion and computing efficiency decay,may arise with such numerical models when dealing with the thin water film.This paper presents a numerical model comprising of the tire,water film,and the interaction with the runway,applying a mathematical model using the smoothed particle hydrodynamics and finite element(SPH-FE)algorithm.The material properties and geometric features of the tire model were included in the model framework and water film thicknesses from 0.75 mm to 7.5 mm were used in the numerical simulation.Furthermore,this work investigated the impacts of both surface texture and the runway permeability.The interaction between tire rubber and the rough runway was analyzed in terms of frictional force between the two bodies.The SPH-FE model was validated with an empirical equation proposed by the National Aeronautics and Space Administration(NASA).Then the computational efficiency of the model was compared with the traditional coupled Eulerian-Lagrangian(CEL)algorithm.Based on the SPH-FE model,four types of the runway(Flat,SMA-13,AC-13,and OGFC-13)were discussed.The simulation of the asphalt runway shows that the SMA-13,AC-13,and OGFC-13 do not present a hydroplaning risk when the runway permeability coefficient exceeds 6%.

Printability and hardening performance of three-dimensionally-printed geopolymer based on lunar regolith simulant for automated construction of lunar infrastructure

Using an in situ lunar regolith as a construction material in combination with 3D printing not only reduces the weight of materials carried from the Earth but also improves the automation of lunar infrastructure construction.This study aims to improve the printability of a geopolymer based on a BH-1 lunar regolith simulant,including the extrudability,open time,and buildability,by controlling the temperature and adding admixtures.Rheological parameters were used to represent printability with different water-to-binder ratios,printing temperatures,and contents of additives.The mechanical properties of the hardening geopolymer with different filling paths and loading directions were tested.The results show that heating the printed filaments with a water-to-binder ratio of 0.32 at 80°C can adjust the printability without adding any additive,which can reduce the construction cost of lunar infrastructure.The printability of the BH-1 geopolymer can also be improved by adding 0.3%Attagel-50 and 0.5%polypropylene fiber by mass at a temperature of 20℃to cope with the changeable environmental conditions on the Moon.After curing under a simulated lunar environment,the 72-h flexural and compressive strengths of the geopolymer specimens reach 4.1 and 48.1 MPa,respectively,which are promising considering that the acceleration of gravity on the Moon is 1/6 of that on the Earth.

土木工程材料自愈合行为的若干力学问题与研究进展

为适应未来基础设施和工业化建造需求,如何改变传统土木工程结构和材料组成,打造全新的具有智能能力的基础设施,已经成为新的研究热点.工程结构的抗损坏能力直接影响国家的社会成本和经济效益.为了减少维修养护费用、提升结构的服役寿命,一种可行的方案是建造能够进行损伤自我愈合的拟生命系统.近几年来,微胶囊、电沉积、感应加热、微生物自愈合等技术被应用于土木工程与道路工程中,有望提升工程结构的耐久性及稳定性,延长服役寿命.但是,为提升自愈合工程材料的使用性能、精准预估裂纹扩展轨迹、精确预测材料的使用寿命,需要进一步从机理上解释自愈合行为.本文首先总结了自愈合材料在土木工程中应用的发展历程及研究进展,随后从损伤力学和断裂力学角度出发,分析了在解释和预测自愈合行为时所面临的若干力学问题,并对现有考虑自愈合效应的本构模型及数值算法进行了梳理.为了进一步明确各内外因素对裂纹扩展-愈合的正负耦合效应,从力学角度提出了亟待解决的问题与挑战.

New innovations in pavement materials and engineering:A review on pavement engineering research 2021

Sustainable and resilient pavement infrastructure is critical for current economic and environmental challenges.In the past 10 years,the pavement infrastructure strongly supports the rapid development of the global social economy.New theories,new methods,new technologies and new materials related to pavement engineering are emerging.Deterioration of pavement infrastructure is a typical multi-physics problem.Because of actual coupled behaviors of traffic and environmental conditions,predictions of pavement service life become more and more complicated and require a deep knowledge of pavement material analysis.In order to summarize the current and determine the future research of pavement engineering,Journal of Traffic and Transportation Engineering(English Edition)has launched a review paper on the topic of"New innovations in pavement materials and engineering:A review on pavement engineering research 2021".Based on the joint-effort of 43 scholars from 24 well-known universities in highway engineering,this review paper systematically analyzes the research status and future development direction of 5 major fields of pavement engineering in the world.The content includes asphalt binder performance and modeling,mixture performance and modeling of pavement materials,multi-scale mechanics,green and sustainable pavement,and intelligent pavement.Overall,this review paper is able to provide references and insights for researchers and engineers in the field of pavement engineering.

Synthesis and characterization of geopolymer from lunar regolith simulant based on natural volcanic scoria

In this study,a new GVS(Ground Volcanic Scoria)lunar regolith simulant was produced.The similarity between GVS and lunar soil was proved by comparison with Apollo lunar soil samples and other commercial lunar soil simulants.Then,GVS lunar regolith simulant was investigated as the source material for preparing geopolymer to produce building material for lunar colony construction.To study the possibility of preparing geopolymer from GVS lunar regolith simulant and the optimum activator formulation as well as the optimum curing conditions,alkaline activated GVS slurries with different mixing ratios based on an orthogonal test scheme were prepared.The geopolymer products based on GVS were characterized by flexural strength test,compressive strength test,X-ray fluorescence(XRF),X-ray diffraction(XRD),Fourier Transform Infrared Spectroscopy(FTIR),Scanning Electron Microscope coupled with Energy Dispersive Spectroscopy(SEM-EDS),29Si magic angle spinning-nuclear magnetic resonance(29Si MAS-NMR),and 27Al MAS-NMR.The experimental results indicate that changes in the mass ratio of sodium hydroxide and GVS and curing temperature have the most significant influence on the flexural strength and compressive strength,respectively.The GVS-based geopolymer can obtain the highest 28-day compressive strength and 28-day flexural strength up to 75.6 MPa and 6.3 MPa.Microstructural results imply that the changes of Si occurring in a variety of environments that explaining preliminarily about the reaction mechanism of GVS-based geopolymer.This study approves the feasibility of making a geopolymer derived from the GVS lunar regolith simulant and the potential utilization of geopolymer based on lunar regolith for construction of the lunar colony in future space exploration.

Waterbomb-origami inspired triboelectric nanogenerator for smart pavement-integrated traffic monitoring

With a rapid development of intelligent transportation systems(ITSs),traffic monitoring has gained increasing attention.Here,we present a new kind of waterbomb-origami-inspired triboelectric nanogenerator(WO-TENG)as a traffic monitoring system to integrate smart pavement with lightweight,cost-effective,excellent deformability,flexibility,and self-rebounding properties.The electrical performance is significantly improved by more than 67%compared with current origami-based TENG,and multi tribo-pairs have great synchronicity.The fully-packaged self-driven WO-TENG is further developed to integrate smart pavement,which can successfully decouple the influence of vehicle speed and weight on the sensing accuracy.This phenomenon demonstrates the feasibility and stability of the WO-TENG for traffic monitoring.Independently of the voltage amplitude and time interval electrical wave,vehicle speed,number of vehicles,and types of vehicles can be further evaluated accurately.This work can not only address the challenge of traditional traffic monitoring system,but also promote the development of TENG based self-powered sensors in ITSs.