Experimental Study On Performance Of Asphalt Mixtures Based On Particle Shape Of Coarse Aggregate And Gradation

Asphalt mixture is viewed as a composite material of multi-phases consisting of rigid solids separated by continuum of viscous cement. Due to mechanical properties of viscoelastic plasticity of asphalt binders, response of the mixtures to load is basically nonlinear and very sensitive to the temperature. On the other hand, the mechanical property of the asphalt mixture depends also upon the interlock of the particles characterized by the shape and gradation of the aggregates used in the mixture. Importance of the aggregate composition can not be overemphasized since the volume fraction of aggregates is normally around 90% of the total volume of the mixture in practice. In this thesis, the investigations include the following several aspects:1. Strength analysis for aggregates of asphalt mixtures, aggregate suspension (AC-20I), SUP-19, stone-to-stone contact and interstitial structure (AM-20) and stone-to-stone contact and close-grained structure (SMA-20) were used for samples; contrast research about shear strength of asphalt mixture for four typical types was done through test. Large-size direct shear apparatus for coarse aggregates was used; shear strength affected by aggregates of sphere-shaped and ellipsoid-shaped was discussed. As a result, for aggregate gradation, SMA-20 yielded significantly higher shear strength when compared with the other types; there was no great difference on the shear strength of AM-20 and SUP-19; but AC-20I yielded lowest shear strength. For aggregate shape, aggregate shape was most sensitive for SMA-20 and SUP-19. Shear strength for stone-to-stone contact and close-grained structure was undertaken by coarse aggregate. Mixtures filled by fine aggregate redundantly could develop lower shear strength than unfilled.2. Sensitivity research for geometric shape of aggregates skeleton. Angularity-shaped crushed stone and well-rounded cobble are used for coarse aggregate, the cobble can be described by sphere-shaped and ellipsoid-shaped. Influence of particle shape on VCA_DRC for skeleton structure is tested. Results confirm that VCA_DRC formed by crushed stone is obviously higher than VCA_DRC formed by cobble. Among cobble, VCA_DRC formed by ellipsoid is higher than VCA_DRC formed by sphere. VCA_DRC formed by single group of aggregates have little discrepancy. Because of filling among several groups, VCA_DRC formed by each grade of aggregates are lower than VCA_DRC formed by each single group of aggregates. The most important elements influencing the value of VCA_DRC are the property of aggregates, such as particle shape in this paper's research. Gradation had weaker effect to the result. Considering experimental conditions in this paper, changes of the value of VCA_DRC for well-rounded cobble with gradation are obvious. The combination of different particle shape would lead to the relative VCA_DRC value changes for the same grade distribution.3. Sensitivity analysis for parameter of laboratory experiment methods. Calculation method and actual measurement using vacuum process for TMD of suspension structure (asphalt mixtures) are analyzed and compared. VV, VMA, VFA influenced by TMD obtained by the method listed above are analyzed and calculated. TMD can be affected remarkably by asphalt filling aggregates. Meanwhile, the 4 kinds of computation methods of volumetric property of asphalt mixtures are compared and analyzed.4. Research for physical behavior of asphalt mixture impacted by geometric shape of aggregates. Three typical proportioning mixture of SMA-20 is chose for Marshall and SGC forming. By determination and contrastive analysis in the volume index of asphalt mixture, we can find that compared to mixture composed by well-rounded cobble, VV, VMA and VCA_mix of mixture formed by angularity-shaped crushed stone is greater. Further more, resistance to deformation and stability of angularity-shaped crushed stone are higher.When the same particle shape, the same compaction condition ,the same bitumen content and SMA-20 are discussed, bulk density of the compacted specimen for coarse grading is maximum, VV,VMA and VCAmix is minimum; bulk density of the compacted specimen for fine grading is minimum, VV,VMA and VCA_mix is maximum; the index for medium grading is medial.