Qun Yang

New asphalt pavement failure criterion based on unified strength theory

This study aims to introduce an appropriate analytical method for asphalt pavement based upon unified strength theory (UST). The traditional maximum shear stress strength theory (MSST) cannot describe the marked difference between tension strength and compressive strength or variable intermediate principal stress, which significantly affects the geotechnical materials. Our studies try to find a new asphalt pavement failure criterion that considers the influence of both tension-compression strength ratio and intermediate principal stress of asphalt mixture. In order to select a suitable theory on pavement material, the UST is introduced and compared with the traditional theory. Results show that the tension-compression strength ratio of asphalt mixture, which is used as a material parameter, dramatically affects the stress and stress distribution law in pavement; the pavement stress level increases dramatically after considering the intermediate principal stresses. Therefore, the UST which considers both tension-compression strength ratio and intermediate principal stress is more in line with the material characteristics of asphalt pavement.

Genetic Algorithms Based Traffic Signal Optimization at a Congested Intersection

The objective of this paper is to investigate genetic algorithms (GA) on traffic signal timing at a congested isolated intersection. The objective function for GA modeling was established on the strategy of minimizing average delay and GA was applied to search for the optimal signal timing. Then microsimulation is used to compare the optimized timings produced by the GA with those obtained for the same intersection using Synchro. Results indicated that applying GA results in lower values of average delay and average number of stops in congested condition than applying Synchro.

Resistivity-temperature characteristics of conductive asphalt concrete

The changes of resistivity of conductive asphalt concrete at different temperatures were studied, and positive temperature coefficient (PTC) model was established to estimate the influence of temperature on the resistivity quantitatively, which eliminated the interference with conductivity evaluation brought by temperature variation. Finally, the analysis of temperature cycling test results proves that the changes of percolation network structure caused by temperature variation prompt the emergence of PTC of conductive asphalt concrete.

Quantitative analysis on distribution of modifier in microstructure of SBS modified asphalt

A method was developed to make a quantitative analysis of the microstructure of asphalt modified with styrene-butadiene-styrene block (SBS) copolymer. Moreover, both mixed and branched SBS were employed in the preparation of modified asphalt. By sampling specimens from the top, middle, and bottom, a number of microscope slides were made and 400 times micro images were gained. Binarized with the software of MATLAB, the images then went to the process of distribution test, when four typical distributions were employed to investigate the distribution of modifier spread in asphalt. The distribution characteristic and its parameter were both found. The results show that asphalt phase clearly obeys Poisson distribution, and its parameter, λ, is bond up with the condition SBS performs in. Based on this parameter, indexes can be set up to evaluate the structure of the mixture and its performance as well. Compared with that modified with mixed SBS, the asphalt modified with branched SBS has better performance but worse stability, for it is easier to segregate.

Laboratory and Field Studies on Construction Opportunity of Porous Concrete Overlay in Tunnel

The double-layer pavement design with a combination of normal concrete layer and porous concrete overlay is the promising way towards tunnel pavement. This paper is aimed to confirm the optimal construction opportunity of porous concrete overlay based on the mechanical behavior of tunnel pavement. Parameters like compressive strength, shearing strength and tensile splitting strength were examined in laboratory and field experiment respectively. It is observed that the strength of the pavement gradually decreases with the increase of the construction time interval between the two layers. The results have revealed that the reasonable construction opportunity of porous concrete overlay should be controlled between the initial setting time and the final setting time of normal concrete layer.

Enhanced Cell Transmission Model for Oversaturated Two Ways Arterials

The cell transmission model (CTM) is a potential simulation tool because it can accommodate all traffic conditions from light condition to oversaturated condition. This research aims to develop a traffic flow feature to improve the modeling of two-way arterials so that they are capable of modeling oversaturated conditions. Two improvements of the CTM are made to adequately study two-way arterials in oversaturated conditions. This enhanced model, proposed as the Conditional Cell Transmission Model (CCTM), is compared with Highway Capacity Software 2000 (HCS) in terms of travel speed. The consistency between the HCS 2000 and the CCTM show