Performance Grade (PG) bitumen undergoes grading based on its performance under various temperatures, a method designed by the Long-Term Pavement Performance (LTPP). This approach determines the highest and lowest pavement temperatures and selects bitumen performing well within that range.
Penetration and viscosity grading, while common, possess limitations in fully characterizing asphalt binder for Hot Mix Asphalt (HMA) pavement. To address this, the Superpave research initiative developed new tests and specifications aiming to more accurately characterize asphalt binders, considering parameters such as rutting, fatigue, and thermal cracking in HMA pavements.
The Superpave Performance Grading (PG) system correlates asphalt binder properties with specific usage conditions, accounting for expected climate and aging effects. It utilizes a battery of tests, specifying the temperatures at which binders must pass, tailored to the prevailing climatic conditions. This system offers more precise relationships between asphalt properties and field conditions compared to traditional grading methods.
How to read a PG Grade?
The PG grading denotes two temperatures—high and low pavement service temperatures—pertinent to the binder’s performance under varying climatic conditions. For instance, a binder identified as PG 64-10 should meet performance criteria at an average 7-day maximum pavement temperature of 64°C and a minimum pavement temperature of -10°C.
The PG system’s notation signifies the binder’s ability to perform satisfactorily within the specified temperature range with a minimum 98% confidence level under normal traffic conditions throughout its service life. Polymer-modified binders, offering enhanced performance and durability, are often utilized to address specific challenges such as rutting resistance in high temperatures and thermal cracking resistance in low temperatures.
A rule of thumb for identifying polymer-modified binders involves summing up the low and high temperature grades—if the total surpasses 90, it’s likely a polymer-modified binder. For instance, a PG 76-22, totaling 98, is likely polymer-modified, whereas a PG 64-10, totaling 74, is likely unmodified
Specification of Performance Grade(PG) Bitumen – Unmodified
|
PG 46-34
|
PG 46-28
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PG 52-28
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PG 58-28
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PG 58-22
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PG 64-22
|
AASHTO Method
|
|
|---|---|---|---|---|---|---|---|
| Original Binder | |||||||
| Flash Point, COC,°C |
230
|
T 48 | |||||
| Flash Point, P-M, °C |
NS
|
≥ 204
|
ASTM D93 | ||||
| Rotational Viscosity @ 135°C, Pa·s |
3.00
|
T 316 | |||||
| Dynamic Shear @ Grade Temperature,°C |
46
|
46
|
52
|
58
|
58
|
64
|
T 315 |
| G*/sin @ 10 rad/sec, kPa |
≥ 1.00
|
||||||
| RTFOT Residue | |||||||
| Mass Loss, % |
≤ 1.00
|
T 240 | |||||
| Dynamic Shear @ Grade Temperature,°C |
46
|
46
|
52
|
58
|
58
|
64
|
T 315 |
| G*/sin @ 10 rad/sec, kPa |
2.20
|
||||||
| PAV Residue (Aging Temperature, °C) |
90
|
100
|
R 28 | ||||
| Dynamic Shear @ Grade Temperature,°C |
10
|
13
|
16
|
19
|
22
|
25
|
T 315 |
| G*/sin @ 10 rad/sec, kPa |
5000
|
||||||
| Creep Stiffness |
-24
|
-18
|
-18
|
-18
|
-12
|
-12
|
|
| S, Mpa |
≤ 300
|
T 313 | |||||
| m-value |
≥ 0.30
|
T 313 | |||||