Effects of Aggregate Size and Specimen Scale on Asphalt Mixture Cracking Using a Micromechanical Simulation Approach

A micromechanical model based on discrete element method（DEM） was employed to investigate the effects of aggregate size and specimen scale on the cracking behavior of asphalt mixture. An algorithm for generating three-dimensional aggregates that can reflect the realistic geometry such as shape, size and fracture surface of aggregate particles was developed using a user-defined procedure coded with FISH language in particle flow code in three-dimensions（PFC3 D）. The parallel-bond model（PBM）, linear contact model（LCM）, and slip model（SM）, whose sets of micro parameters were obtained by comparing experimental tests with numerical simulation results, were used to characterize the internal contact behavior of asphalt mixture. Digital asphalt mixture specimens were used to simulate the effects of aggregate size and specimen scale on the cracking behavior by the indirect tensile（IDT） test. Some conclusions can be drawn as follows： Both cracks and IDT strength decrease with increasing aggregate size. However, the heterogeneity of contact-force distribution augments with increasing aggregate size, especially with 13.2-16 mm aggregate. The aggregate size of 4.75-9.5 mm dominates in forming skeleton structure for asphalt mixture. The IDT strength decreases and cracks augment with increasing sample scale. The crack growth can be well interpreted from the perspective of energy analysis. The conclusions show that the proposed micromechanical model is suitable for the simulation of crack propagation. This study provides an assistant tool to further study the cracking behavior of particle-reinforced composites material such as asphalt mixture and Portland cement concrete.

The Application of Curriculum Ideological and Political Cases in the Teaching of Road Survey and Design

Ideological and political construction of curriculum is the key link to implement the fundamental task of moral education.Focusing on the training objectives of civil engineering professionals in the new era,combined with the teaching concepts of moral education and student-centered education,the teaching objectives for the course of road survey and design have been re-set.The implementation plan of ideological and political education has been put into practice by involving excellent engineering cases,stories of outstanding figures in this field,traffic accidents,design concepts and technological innovation to explore the methods of integrating ideological and political cases into curriculum teaching for a continuous improvement of the promotion of curriculum ideological and political education to the teaching quality of professional courses.

Investigating safety and liability of autonomous vehicles:Bayesian random parameter ordered probit model analysis

Purpose–This study aims to investigate the safety and liability of autonomous vehicles(AVs),and identify the contributing factors quantitatively so as to provide potential insights on safety and liability of AVs.Design/methodology/approach–The actual crash data were obtained from California DMV and Sohu websites involved in collisions of AVs from 2015 to 2021 with 210 observations.The Bayesian random parameter ordered probit model was proposed to reflect the safety and liability of AVs,respectively,as well as accommodating the heterogeneity issue simultaneously.Findings–The findings show that day,location and crash type were significant factors of injury severity while location and crash reason were significant influencing the liability.Originality/value–The results provide meaningful countermeasures to support the policymakers or practitioners making strategies or regulations about AV safety and liability.

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.

Inverse determination of multiple heat sources’ release history in indoor environments

The heat source of an air-conditioned room has an important effect on the indoor environment. The release rates of heat sources are related to the comfort of the designed thermal environment, so they must be determined. Traditional design methods rely on iterative guess-and-correct, which consumes resources and time and cannot meet the needs of modern design. This study aims to establish an inverse model of Tikhonov regularization and least square optimization by using computational fluid dynamics (CFD), so that researchers can accurately determine the time release rate of multiple heat sources with known parameters. The temporal release rates can then be solved based on the inverse matrix operation with the temperature series at different discrete times. The study speeds up the solving process and expresses the temperature as the convolution integral between the temperature response of the thermal response factor and the arbitrary release rate. The results show that applying the above method to the quantization of the temporal release rates of three heat sources in a three-dimensional cavity can correctly determine the temporal release rates of multiple heat sources. The errors between the inversely determined release rates and the actual release rates are less than 40%.