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Open graded friction course (OGFC) is effective in improving the surface function of asphalt pavements. However, it is prone to clogging including deformation-related and particle-related clogging. The aim of the research reported in this paper is to investigate the permeability loss or reduction due to deformation-related clogging and explore the critical size of solid particles attributed to OGFC particlerelated clogging. A special falling head permeameter was developed with consideration of both rainwater flowing procedure and the pavement transversal slope. Eight types of OGFC mixtures with different air void contents, gradations, and nominal maximum aggregate sizes were prepared for deformation-related clogging evaluation. Wheel rutting tests were conducted on the OGFC samples with different loading times under two load levels [(1) 700 kPa, and (2) 900 kPa] at 45 and 60°C, and next were permeability tests using the developed permeameter. Permeability loss after different wheel loading times were calculated to explore the effects of the initial air void content, nominal maximum aggregate size, temperature, and loading pressure on deformation-related clogging. Furthermore, seven types of suspension liquids were prepared for particle-related clogging evaluation. For each suspension liquid, the proportions of solids trapped in OGFC air void, passing OGFC sample, and retained on the sample surface were calculated after permeability tests to determine the critical sizes of particle attributed to particle-related clogging. Results show that with the increase in wheel loading times, the permeability of OGFC mixture shows a steady decrease after a sharp initial decline. Permeability loss due to deformation-related clogging can be reduced effectively by using larger nominal maximum aggregate size and larger air voids. Values of 0.15-0.3 and 1.18-2.36 mm are the critical sizes of trapped particles in OGFC mixtures. [ABSTRACT FROM AUTHOR]

A theoretical model was introduced for designing the rubberized asphalt mixtures and validated by mixture tests in this paper. This model is comprised of three parts: fine aggregate gradation design, coarse aggregate gradation design and mixture volumetric design. The rubberized asphalt mixture with a nominal maximum aggregate size of 13 mm (AR-13) was designed with this model. The orthogonal experimental design method was then employed to study the effect of design parameters (air voids (VV), voids in mineral aggregate (VMA) and Fuller-curve's exponent n) on the rutting performance of the mixture. The orthogonal experimental results indicate that the VV and VMA are the two key parameters which affect the rutting performance of the rubberized asphalt mixtures. The design parameter optimal combination and performance requirements of AR-13 were finally recommended based on the experimental results and previous experiences in China and America. [ABSTRACT FROM AUTHOR]

The degradation behavior and mechanism of aggregate used for hot mix asphalt (HMA) mixtures has been investigated in this study. Laboratory tests, including the crushing test, Marshall compactor test, and Superpave gyratory compactor test, were used to evaluate the degradation behavior of single-size aggregate and/or graded aggregates. In order to verify the laboratory test results, the degradation of field HMA materials extracted from asphalt pavements after long-time service was also evaluated. The stress-transfer model for an aggregate skeleton was analyzed in order to provide a fundamental understanding of the stress distribution and degradation mechanism of the aggregate system. The results indicate that the degradation of the aggregate gradation is not random and has a fixed internal trend. The 4.75 mm aggregate proved to be the demarcation point between coarse and fine aggregate. During the degradation process, coarse aggregate tends to break into graded aggregate to form a well-balanced skeleton to bear an external load, and the 4.75 mm aggregate plays a key role in the graded aggregate. The crushing test and Super-pave gyratory compactor test proved to be easily done and promising for capturing the degradation of aggregate and the gradation of HMA. The variation in the retained percentage of 4.75 mm aggregate and the breakdown ratio of the original aggregate and/or gradation can quantitatively depict the degradation of HMA aggregate. [ABSTRACT FROM AUTHOR]

The purpose of this study is to evaluate the residual strength of reclaimed asphalt pavement (RAP) to understand the strength forming mechanism of RAP in cold recycled asphalt mixture. The mechanical properties of the RAP were investigated as compared to the properties of pure aggregates. Triaxial shear tests were conducted to analyze the residual cohesion of asphalt binder in the RAP. The gradation and specific surface area of RAP were analyzed to understand the agglomeration structure of coarse RAP particles. Splitting strength of cement-RAP mixtures was tested as compared to cement-aggregate mixtures. It can be concluded that the RAP in the cold recycled asphalt mixture does not act exactly like "black color" aggregates. The aged asphalt in the RAP has active cohesion although its cohesion strength is much lower than the binder in the hot-mix asphalt mixture. The coarse RAP particles formed by agglomeration of fine particles and the aged binder have important influences on the strength of cold recycled asphalt mixtures. The cement-RAP mixture has much lower splitting strength than the cement-aggregate mixture with the same gradation and cement content. It is important to add new aggregate into the recycled mixture to increase the effective aggregate surface area that can be coated with the new binder. [ABSTRACT FROM AUTHOR]