Binder Tests
Tests that grade and characterize asphalt binder: the Superpave tests and aging procedures, and the older penetration, ductility and softening point tests.
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Overview
Asphalt Binder and Characterization
The asphalt content and gradation test can be used for HMA quality control, acceptance testing or forensic analysis. The three major test methods, solvent extraction, nuclear asphalt content gauge and ignition furnace are discussed here.
Superpave performance grading tests
Rotational Viscometer
The Rotational Viscometer (RV) (Figure 1 and Figure 2) is used to determine the viscosity of asphalt binders in the high temperature range of manufacturing and construction.
Rolling Thin-Film Oven
The Rolling Thin-Film Oven (RTFO) procedure (Figure 1) provides simulated short term aged asphalt binder for physical property testing. Asphalt binder is exposed to elevated temperatures to simulate manufacturing and placement aging.
Pressure Aging Vessel
The Pressure Aging Vessel (PAV) (Figure 1) provides simulated long term aged asphalt binder for physical property testing. Asphalt binder is exposed to heat and pressure to simulate in-service aging over a 7 to 10 year period.
Dynamic Shear Rheometer
The dynamic shear rheometer (DSR) (Figure 1 and Figure 2) is used to characterize the viscous and elastic behavior of asphalt binders at medium to high temperatures.
Bending Beam Rheometer
The Bending Beam Rheometer (BBR) test (see Figure 1) provides a measure of low temperature stiffness and relaxation properties of asphalt binders.
Direct Tension Tester
The Direct Tension Tester (DTT) test (see Figure 1, 2) provides a measure of low temperature stiffness and relaxation properties of asphalt binders.
Earlier grading tests
Penetration Test
Aside from chewing, the penetration test is the oldest asphalt test. In 1888, H.C. Bowen of the Barber Asphalt Paving Company invented the forerunner to the penetration test, the Bowen Penetration Machine (Halstead and Welborn, 1974).
Absolute Viscosity
Viscosity is simply a measure of a fluid’s resistance to flow and is described by the following equation:
Kinematic Viscosity
The kinematic viscosity of a liquid is the absolute (or dynamic) viscosity divided by the density of the liquid at the temperature of measurement.
Ductility
The ductility test (Figure 1) measures asphalt binder ductility by stretching a standard-sized briquette of asphalt binder (Figure 2) to its breaking point. The stretched distance in centimeters at breaking is then reported as ductility.
Softening Point
The softening point is defined as the temperature at which a bitumen sample can no longer support the weight of a 3.5-g steel ball. Although it is commonly used in Europe, it is mostly used for roofing asphalts in the U.S.
Thin-Film Oven
The thin-film oven (TFO) test simulates short-term aging by heating a film of asphalt binder in an oven for 5 hours at 163° C (325° F).
Flash Point
A typical flash point test involves heating a small sample of asphalt binder in a test cup. The temperature of the sample is increased and at specified intervals a test flame is passed across the cup.
Spot Test
The spot test is used to determine whether or not an asphalt cement has been damaged during processing due to overheating. This damage, called "cracking", occurs because the actual molecules are thermally broken apart.
More
ΔTc and Continuous Grading
Continuous PG grades and ΔTc, the BBR-based measure of how well an aged binder relaxes stress, with the calculation and a worked example.
Multiple Stress Creep Recovery Test
The MSCR test on the DSR: repeated creep and recovery at two stress levels, how Jnr and percent recovery are calculated, and how they grade a binder.