Page 47 - Mechanics of Asphalt Microstructure and Micromechanics

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40 Ch a p t e r w o

2.1.9.4 Material Volumetric-Flow Rate (MVR)
Shenoy (2001b, 2002) showed that the material’s volumetric-flow rate (MVR) in cc/10
min can be used to correctly determine the high temperature performance grade speci-
fication of asphalt binders. The MVR can be determined using a relatively inexpensive
and portable flow measurement device (FMD). Through determination of the volumet-
ric-flow rate, the fundamental viscoelastic data curves obtained from the DSR testing
could be unified. The MVR is the material volume (in cubic centimeters) that is ex-
truded in 10 min through the capillary die of a certain diameter and length of a FMD.
The extrusion takes place by applying “dead weight” pressure under certain tempera-
ture conditions. The volume-flow rate is easy to measure and does not need the mate-
rial density for the calculations. The flow measurement device consists of a steel cylin-
der provided with a calibrated thermocouple surrounded by insulated heaters that can
control the temperature. The heaters can maintain a constant temperature at 10 mm
above a steel die during the test. A 9.5 mm steel piston is used to extrude the material
through the die, which has an internal diameter of 2.1 mm.
A modified frequency can be calculated with the following formula for |G*|/sinδ
= 1 kPa:
⎛ 1/ n ⎞
L
ω ⎜ ⎝ MVR⎠ ⎟ 0 245 (2-16)
.
where w = modified frequency
L = load (kg)
n = power-law index corresponding to the slope of the load L

2.1.9.5 Handling and Pumping–Asphalt Flow Characteristics
The Brookfield rotational viscometer was adopted in Superpave to determine the vis-
cosity of asphalt binders at construction temperatures above 100°C (Roberts et al., 1996).
The test measures the original or modified binder viscosity for mixing and pumping
operations. Rotational viscosity is determined by measuring the torque that maintains
a constant rotational speed (20 rpm) of a cylindrical spindle submerged in asphalt at
275°F (135°C). Superpave binder specifications limit the viscosity to 3 Pa.s at 135°C. The
method was proposed by the FHWA and AASHTO and is covered under ASTM D4402
or AASHTO TP48.

2.1.9.6 Permanent Deformation and Fatigue Cracking —Rutting and Structural Cracking
These performance parameters can be evaluated using the DSR. Samples from original
binder, rolling thin film oven (RTFO) tests, and pressure aging vessel (PAV) tests are
placed between a fixed base plate and an oscillating plate (Asphalt Institute, 2007). All
Superpave DSR asphalt tests are performed at 10 rad/s (1.59 Hz or cycles/s). There are
two types of DSRs: controlled stress and controlled strain. Controlled stress rheometers
work by applying a fixed torque to oscillate the plate while the controlled strain rheom-
eters oscillate the plate at a specified frequency and measure the required torque. De-
pending on the binder’s stiffness, the torque necessary to move the plate at the recom-
mended frequency will vary. DSR testing method characterizes both viscous and elastic
behavior of asphalt at high and intermediate temperatures by measuring its complex
shear modulus (G*) and phase angle (δ). Results are automatically reported by the rhe-