How to Read Performance Grades of Asphalt Binder

By Hongbin Xie, Graniterock RTS

Background
Asphalt binders are most commonly graded by their physical properties. An asphalt binder's physical backdrop straight describe how it will perform as a elective in asphalt concrete (Ac) pavement. Although cobblestone binder penetration and viscosity grading is all the same commonly used worldwide, new binder tests and specifications are developed to more accurately narrate cobblestone binders for use in AC pavements.

The nigh advanced cobblestone folder grading system is Performance Graded (PG) System, which is resulted from the $fifty million Strategic Highway Enquiry Program (SHRP) and has been adopted by all of the other 49 states in the U.S.

In the past, Caltrans has classified binder using viscosity grading based on Aged Residue (AR) System. Caltrans started to use the PG system since January 1, 2006, and will start to use the PG system for polymer modified binder on Jan one, 2007.

WHAT IS PG SYSTEM?
Performance grading is based on the thought that asphalt binder properties should exist related to the weather under which it is used. PG asphalt binders are selected to run across expected climatic conditions also as crumbling considerations with a sure level of reliability. Therefore, the PG arrangement uses a common ready of tests to measure physical properties of the binder that can exist straight related to field performance of the pavement at farthermost temperatures. A folder graded past PG system should see all specified criteria by this common set of tests.

The typical prepare of binder testing for PG system is shown in Figure 1. The Rotational Viscometer (RV) test is used to evaluate the pumpability at the asphalt constitute. The Dynamic Shear Rheometer (DSR) tests with different levels of aging are used to evaluate the binder properties at high or intermediate temperature, which are related to the rutting or fatigue groovy of pavement failure modes. The Bending Beam Rheometer (BBR) and Direct Tension Exam (DTT) with certain level of crumbling are used to evaluate the binder properties under depression temperature, which are related to the depression temperature corking of pavement failure style.

The Rolling Thin Motion picture Oven (RTFO) aging is used to simulate the brusque-term aging of the asphalt binder during the construction phase, including the mixing, silo, transportation and lay down etc. The Pressure Crumbling Vessel (PAV) aging is used to simulate the long-term crumbling of the asphalt binder after the AC pavement in service about x years.

HOW TO READ A PG Form?
The PG grading system is based on climate, so the grade annotation consists ii portions: high and low pavement service temperature. The major concern for loftier temperature performance is rutting, which typically takes time to cumulate, therefore an average of 7 day maximum pavement temperature is used for describing the high temperature climate. On the low temperature side, thermal slap-up can happen during one really cold night; therefore the minimum pavement temperature is used for describing the low temperature climate. For both high and low temperature grade, PG grades are graded in vi°C increase. The boilerplate 7 day maximum pavement temperature typically ranged from 46 to 82°C, and minimum pavement temperature typically ranged from −46°C to −10°C.

A binder identified equally PG 64-x must run into performance criteria at an average vii day maximum pavement temperature of 64°C and likewise at a minimum pavement temperature of −10°C. Delight notation that maximum pavement temperature is typically higher than the air temperature by about 20°C since the night colour pavement absorbs the heat and retains it. The maximum pavement temperature is typically measured at about 1 inch below the pavement surface. However, the minimum pavement temperature occurs on the surface of the pavement and is equal to the air temperature.

The common minimum reliability used is 98%, so that means when the PG 64-x binder is selected, the asphalt binder in the AC pavement should perform satisfactorily under normal traffic condition at the location where the extreme pavement temperature are within the range of −10°C and 64°C throughout its service life with a minimum 98% conviction level. Where the traffic condition is not typical, such as the really heavy traffic like interstate highway, or deadening traffic such as autobus end or intersection surface area, one or two grades stiffer asphalt binder may be used to help prevent the rutting problem.

Polymer modified binders are used wherever actress performance and immovability are desired. Improvement in resistance to rutting, thermal cracking, fatigue impairment, stripping, and temperature susceptibility have led polymer modified binders to exist substituted for asphalt in many paving and maintenance applications. Especially when expert rutting resistance for loftier temperature and skilful thermal smashing resistance for low temperature are concurrently required in the same application, the polymer modification is generally required.

A rule of thumb to differentiate the polymer modified binder from unmodified binder is to add both low and high temperature grades together, if the sum is greater than 90, it is probable to be a polymer modified folder. For case, a PG 76-22 is probable to be a polymer modified binder since the sum is 98, while a PG 64-x is probable to exist an unmodified since the sum is 74. Polymer modified binders used in Caltrans projects will exist noted with Polymer Modified (PM), such as PG 64-28PM, or PG 76-22PM.

The Caltrans climate regions used for selecting cobblestone binder grade is listed in Table 1.

For conventional Dense Graded Asphalt concrete, values are given for typical and special conditions. Special conditions are defined as those roadways or portion of roadways which meet any of the following criteria:

Truck/motorcoach traffic (over 10 million ESALs for twenty years)
Truck/bus stopping areas (parking area, residuum area, loading area, etc.)
Truck/bus stop and become areas (intersections, metered ramps, ramps to and from Truck Scales etc.)

Folder			Conventional	Asphalt		Rubberized	Asphalt
			Dense Graded	Open Graded		Gap Graded	Open Graded
Climatic Region	PG	PG	PG Polymer Modified	PG	PG Polymer Modified(2)	PG	PG
Due south Coast, Primal Coast, Inland Valleys	64-10	70-10	64-28PM	64-10	58-34PM	64-sixteen	64-16
N Coast	64-sixteen	—	64-28PM	64-16	58-34PM	64-16	64-16
Low Mount, South Mountain	64-sixteen	—	64-28PM	64-16	58-34PM	64-xvi	64-16
High Mount, High Desert	64-28	—	58-34PM	64-28	58-34PM	58-22	58-22
Desert	70-10	—	64-28PM	70-10	58-34PM	64-16	64-sixteen

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Source: https://www.graniterock.com/technical_reports/performance-grade-system-for-asphalt-bin?category_id=89

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