1. Effects of coarse aggregate 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. 4. OUTLINE INTRODUCTION MATERIALS & METHODS
RESULTS & DISCUSSION 3.
CONCLUSIONS 4.

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

4. INTRODUCTION
Road quality=High/low temperature performance+ Skid resistance……
Aggregate
(Skeleton)
Asphalt(Bonding & filling)
95%wt
5%wt
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. Characterization method
INTRODUCTION
Previous studies
Objective
Assessment is
not quantitative
Effects on
macro-performance
is rarely studied
Propose quantitative
Characterization method
micro-performance

7. INTRODUCTION
Map of this research

8. Los Angeles abrasion apparatus
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. Percentage passing（%）of the sieve（mm）listed below
MATERIALS & METHODS
mixtures
design
AC-16, optimum asphalt content %
SMA-16, optimum asphalt content %
Marshall test
Gradation of asphalt mixture
Gradation types
Percentage passing（%）of the sieve（mm）listed below 19 16
13.2
9.5
4.75
2.36
1.18
0.6
0.3
0.15
0.075
AC-16
100 93 80 62 40 30 22
17.5
12.5 6
SMA-16 95 75 55 26
19.5 18 15
11.5 10

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

11. MATERIALS & METHODS Data processing Specimen scanning Cubical boxes
X-ray CT system
Three perspectives of images
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)
AIMS II- Gradient angularity (GA)
XCT-Three-dimensional angularity (3DA)
Different correlation coefficient R2 with two placed states
Evaluation indexes of morphological characteristics
4.75mm
9.5mm
13.2mm
16mm
Gradient angularity (GA)
0.003
0.088
0.035
0.085
Three-dimensional angularity (3DA)
0.81
0.69
0.863
0.945

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
Dynamic stability (DS)
Rutting depth (RD)
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
134
100 63
150
100 63
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