1 Introduction
1.1 Aggregate gradation
2 Materials used
Property | Results | IRC SP 79 requirements |
---|---|---|
Aggregate impact value | 15.89 % | 24 % maximum |
Los Angeles abrasion value | 16.40 % | 25 % maximum |
Water absorption | 0.35 % | 2 % maximum |
Specific gravity test | 2.64 | – |
Combined flakiness and elongation index | 23.5 % | 30 % maximum |
Property | Results obtained |
---|---|
Penetration (100 gramme, 5 s at 25 °C) (1/10th of mm) | 60.4 |
Softening point, °C (Ring & Ball Apparatus) | 59 |
Ductility at 27 °C (5 cm/min pull) (cm) | > 100 |
Flash point (°C) | 244 |
Viscosity at 150 °C, poise | 3.5 |
Test on residue for thin film oven tests | |
Loss in mass (%) | 0.088 |
Increase in softening point (°C) | 4 |
Reduction in penetration of residue (at 25 °C %) | 22.5 |
Elastic recovery of half thread in ductilometer at 25 °C (%) | 65 |
IS sieve size (mm) | Cumulative % by weight of total aggregate passing | |||
---|---|---|---|---|
SMA 1 (NMAS 16 mm) | SMA 2 (NMAS 13 mm) | |||
Range | Adopted | Range | Adopted | |
19 | 100 | 100 | 100 | 100 |
16 | 90–100 | 95 | – | – |
13.2 | 60–80 | 70 | 90–100 | 95 |
9.5 | 40–60 | 50 | 50–75 | 62.5 |
4.75 | 20–32 | 26 | 20–28 | 24 |
2.36 | 18–27 | 22 | 16–24 | 20 |
1.18 | 14–22 | 18 | 13–21 | 18 |
0.6 | 12–19 | 16 | 12–18 | 16 |
0.3 | 10–16 | 14 | 10–20 | 14 |
0.15 | 9–14 | 12 | – | – |
0.075 | 8–12 | 10 | 8–12 | 10 |
Mix design parameters | Requirements |
---|---|
Air void content (%) | 4.0 |
Bitumen content (%) | 5.8 minimum |
Voids in mineral aggregates (VMA) (%) | 17 minimum |
Voids in coarse aggregates mix (VCAMIX) (%) | Less than VCA in the dry-rodded condition (VCADRC) |
Asphalt drain down (%) | 0.3 maximum |
Tensile strength ratio (TSR) (%) | 80 minimum |
3 Experimental investigation
3.1 Drain down
3.2 Volumetric and Marshall properties
Mixture | SMA 1 | SMA 2 | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
Property | Bitumen content by weight of aggregate | Bitumen content by weight of aggregate | ||||||||
5.0 | 5.5 | 6.0 | 6.5 | 7.0 | 5.0 | 5.5 | 6.0 | 6.5 | 7.0 | |
G
MM (g/cm3) | 2.498 | 2.48 | 2.463 | 2.446 | 2.43 | 2.483 | 2.466 | 2.449 | 2.432 | 2.416 |
G
MB (g/cm3) | 2.34 | 2.359 | 2.369 | 2.361 | 2.363 | 2.332 | 2.342 | 2.345 | 2.348 | 2.343 |
VA (%) | 6.32 | 4.90 | 3.81 | 3.50 | 2.77 | 6.09 | 5.03 | 4.25 | 3.47 | 3.03 |
VMA (%) | 17.45 | 17.19 | 17.21 | 17.90 | 18.22 | 18.51 | 18.55 | 18.83 | 19.11 | 19.66 |
VFB (%) | 62.28 | 69.96 | 76.45 | 79.12 | 83.46 | 67.10 | 72.91 | 77.45 | 81.83 | 84.57 |
MS (kN) | 14.64 | 17.66 | 20.1 | 19.17 | 17.83 | 14.58 | 15.69 | 19.35 | 18.83 | 15.06 |
FV (mm) | 3.05 | 3.60 | 4.10 | 4.15 | 4.55 | 3.15 | 3.35 | 3.50 | 3.60 | 3.75 |
MQ (kN/mm) | 4.80 | 4.90 | 4.90 | 4.62 | 3.92 | 4.63 | 4.68 | 5.53 | 5.23 | 4.02 |
VCAMIX
| 39.40 | 39.23 | 39.28 | 39.82 | 40.08 | 38.18 | 38.24 | 38.49 | 38.73 | 39.18 |
VCAMIX/VCADRC
| 0.923 | 0.919 | 0.92 | 0.933 | 0.939 | 0.878 | 0.880 | 0.885 | 0.891 | 0.901 |
OBC (%) | 6.00 | 6.12 |
Property | Mixture | |
---|---|---|
SMA 1 | SMA 2 | |
OBC (%) | 6.00 | 6.12 |
G
MM (g/cm3) | 2.463 | 2.445 |
G
MB (g/cm3) | 2.366 | 2.347 |
VMA (%) | 17.33 | 18.86 |
VFB (%) | 75.72 | 78.73 |
MS (kN) | 19.60 | 19.13 |
FV (mm) | 3.99 | 3.52 |
MQ (kN/mm) | 4.91 | 5.43 |
VCAMIX
| 39.37 | 38.52 |
VCAMIX/VCADRC
| 0.922 | 0.886 |
3.3 Indirect tensile strength (ITS)
SMA Mix | ITS (MPa) | TSR (%) | |
---|---|---|---|
Unconditioned | Conditioned | ||
SMA 1 | 1.110 | 1.013 | 91.26 |
SMA 2 | 0.867 | 0.773 | 89.16 |
3.4 Stripping
3.5 Rutting characteristics
3.6 Fatigue behaviour
Mix type | Average load applied (kg) | % of ITS load | Fatigue life (No. of cycles) |
---|---|---|---|
SMA 1 | 176.45 | 15.04 | 7562 |
386.81 | 32.98 | 2993 | |
579.65 | 49.42 | 1269 | |
SMA 2 | 137.13 | 14.97 | 7256 |
306.78 | 33.49 | 2645 | |
459.36 | 50.15 | 1093 |
4 Discussion and conclusion
-
Both SMA mixtures satisfied drain down requirements without any stabilising additive and this is due to the usage of PMB as binder material.
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SMA 1 mixtures have comparatively higher density, stability and other volumetric and Marshall properties. OBC was found to be slightly less for these mixtures.
-
For SMA 1 mixtures, tensile strength was 28 %–31 % higher than the other mix and moisture resistance was also slightly better.
-
SMA 1 mixture was better resistant to rutting, and in wheel-tracking test, deformations were 0.4–0.7 mm less than SMA 2 slab for all wheel passes. After 10,000 passes rut depth was 4.1 mm for SMA 1, compared to 4.8 mm in the case of SMA 2 slab.
-
At different proportions of ITS loads, fatigue life of SMA 1 mixes were about 10 % higher than SMA 2, whereas at constant tensile stress, the improvement can be minimum 21 %.