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Effects of coarse aggregate angularity on asphalt mixture’s macro performance

This research investigates the effects of coarse aggregate angularity on the macro performance of asphalt mixtures, including surface skidding, pot holes, road quality, rutting, and safe driving. Quantitative characterization methods are proposed, and the results show that angularity has a significant influence on high-temperature performance, compaction performance, and dynamic modulus.

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Effects of coarse aggregate angularity on asphalt mixture’s macro performance

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  1. Effects of coarseaggregate angularity on asphalt mixture’s macro performance Junfeng Gao Ph.D. candidate Chang'an University Michigan Technological University Pretoria, South Africa July 10, 2018

  2. 1. 2. 3. RESULTS & DISCUSSION MATERIALS & METHODS INTRODUCTION OUTLINE 4. CONCLUSIONS

  3. INTRODUCTION How to solve? Surface skidding Pot holes ？？？ +Road quality Rutting Safe driving + good car ≠ 100% driving safety

  4. Aggregate (Skeleton) 95%wt Asphalt(Bonding & filling) 5%wt INTRODUCTION Road quality=High/low temperature performance+ Skid resistance…… Asphalt mixture The mass fraction and volume fraction of aggregates account for more than 90% of the total, which plays a decisive role in the transmission of load and the dispersion of stress and strain. It affects the compaction performance, skid resistance performance and high-temperature stability performance of asphalt pavement.

  5. INTRODUCTION Angularity Shape Coarse aggregate Surface texture • The shape, angularity, and surface texture of the coarse aggregates determine the interlocking and frictional interactions between the aggregates, making a contribution to the formation of good mechanical properties and greater structural strength of the asphalt mixture. • The quantitative evaluation of the morphological characteristics of the coarse aggregate is really important.

  6. INTRODUCTION Previous studies Objective Assessment is not quantitative Propose quantitative Characterization method Effects on macro-performance is rarely studied Effects on micro-performance

  7. INTRODUCTION Map of this research

  8. MATERIALS & METHODS Coarse aggregate SK-90# asphalt Add Your Text 1. A specific weight of coarse aggregate containing different particle sizes was poured into the drum; 2. The lid was closed and polishing times (0,300,1000 times) was set; 3. The Los Angeles abrasion apparatus ran till the polishing was completed. Note: Steel balls were not added to the instrument. Los Angeles abrasion apparatus

  9. mixtures design MATERIALS & METHODS AC-16, optimum asphalt content 4.3% SMA-16, optimum asphalt content 5.5% Marshall test Gradation of asphalt mixture

  10. MATERIALS & METHODS Test methods Wheel tracking test Simple performance test SGC test Size: 300mm×300mm×50mm wheel load: 0.7 MPa Temperature: 60 ℃ Size: Diameter,100mm temperature: 35 ℃ /50 ℃ Frequency: 0.1, 0.5, 1, 5,10,25Hz Size: Diameter,150mm Compaction angle: 1.25° Speed: 30 r/min Compaction strength: 600kPa

  11. MATERIALS & METHODS Data processing Specimen scanning Cubical boxes Three perspectives of images X-ray CT system X-ray CT system and cubical boxes

  12. MATERIALS & METHODS Data processing 3D layers in X-ray CT • Pti, Pri, Pfi are the perimeters of aggregates outlines at the ith CT image of the top, right, and front views, respectively, mm; • Pte, Pre, Pfe are the equivalent ellipse perimeters, mm2; • Ati, Ari ,Afi are the areas of aggregate outlines at the ith CT image of the top, right, and front views, respectively, mm; • n are the total numbers of CT images; • i denotes the ith CT image of aggregate.

  13. MATERIALS & METHODS Data processing • θ is the angle of orientation of the edges; • n is the total number of points; • i denotes the ith point on the edge of the particle. Gradient angularity (GA) & AIMS

  14. RESULTS AND DISCUSSION Accuracy analysis of three-dimensional angularity (3DA) Placed state 1 Placed state 2 Different placed states of the same coarse aggregate

  15. RESULTS AND DISCUSSION Accuracy analysis of three-dimensional angularity (3DA) XCT-Three-dimensional angularity (3DA) AIMS II- Gradient angularity (GA) Different correlation coefficient R2 with two placed states

  16. RESULTS AND DISCUSSION High-temperature performance Dynamic stability (DS) Rutting depth (RD) • Polishing times-increase, coarse aggregate angularity, decrease; angularity has a greater influence on the high-temperature performance • DS-coarse aggregate polished 1000 times; lower than the requirements of the technical specification for highway asphalt pavement construction • The quality of the coarse aggregate should be strictly controlled

  17. RESULTS AND DISCUSSION High-temperature performance Rutting depth (RD) Dynamic stability (DS) • A good linear relationship between 3DA and DS & RD • 3DA is able to characterize the angularity of the coarse aggregate and reflect the high-temperature performance

  18. RESULTS AND DISCUSSION Compaction performance 100 63 134 63 150 100 AC-16 SMA-16 • Compaction times-increase; height-decrease • The more times the coarse aggregates were polished, the faster of the height changed; the lower the coarse aggregate angularity, the easier compaction of the asphalt mixture

  19. RESULTS AND DISCUSSION Dynamic modulus AC-16 at ref. temp. 35℃ AC-16 at ref. temp. 50℃ • The dynamic modulus at all levels increased with the increase of loading frequency • The dynamic modulus tended to decrease with the increase of polishing times, i.e., the decrease of the coarse aggregate angularity, however, this downtrend was not significant

  20. RESULTS AND DISCUSSION Dynamic modulus SMA-16 at ref. temp. 35℃ SMA-16 at ref. temp. 50℃ • The dynamic modulus of SMA-16 decreased with the increase of polishing times, the downtrend was significant, in addition, as the load frequency increased, the change became more significant • AC-16, suspension dense structure, cohesion between the aggregate and asphalt; SMA-16, dense coarse aggregate structure, internal friction generated by the intercalation of the aggregates

  21. CONCLUSIONS (1) The three-dimensional angularity (3DA) has a strong relationship with the macro performance of asphalt mixtures, and it is able to characterize the coarse aggregate angularity. (2) The angularity greatly influences the high-temperature performance and compaction performance of asphalt mixtures. Higher angularity leads to better high-temperature stability but more difficult compaction. (3) The dynamic modulus of asphalt mixtures increases with the increase of the loading frequency. And it decreases with the increase of the temperature. (4) The angularity has different effects on the dynamic modulus of different gradation asphalt mixtures. The coarse aggregate angularity has little effect on the dynamic modulus of the AC-16 asphalt mixture, but has a great influence on the SMA-16 asphalt mixture.

  22. ACKNOWLEDGEMENTS Advisor Hainian Wang Zhanping You

  23. Thanks for your listening & comments

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