The BBR applies a transient creep load in bending mode to load the specimen,
which is held at a constant temperature. The data acquisition system records the load and
deflection results and calculate the creep stiffness, S(t), and m-value, which is the slope
of the stiffness-time relationship at t = 60s.
The creep stiffness of the asphalt binder is a measurement of how the asphalt
binder resists creep loading. It is calculated using the following equation (1):
PL3
S(t) = 3 (3.1)
4bh3g(t)
where
S(t) = creep stiffness at time, t = 60 seconds
P = applied constant load, 100g (980mN)
L = distance between beam supports, 102mm
B = beam width, 12.5mm
h = beam thickness, 6.25mm
6 (t) = deflection at time, t = 60 seconds
The m-value is defined as the slope of the log creep stiffness versus log time
curve at a loading time of 60s. It indicates the rate of change in stiffness with time, S(t).
Below is a plot of m-value. (1)