30 June 2001
PROCEDURES FOR DETERMINING THE FATIGUE LIFE
OF BITUMINOUS CONCRETE
M-1. LABORATORY TEST METHOD.
a. General. A laboratory procedure for determining the fatigue life of bituminous concrete
paving mixtures containing aggregate with maximum sizes up to 31.8 millimeters (1-1/2 inches) is
described in this chapter. The fatigue life of a simply supported beam specimen subjected to third-
point loading applied during controlled stress-mode flexural fatigue tests is determined.
b. Definitions. The following symbols are used in the description of this procedure:
(1) , = initial extreme fiber strain (tensile and compressive, inches per inch)
(2) Nf = fatigue life of the specimen, number of load repetitions to fracture.
Extreme fiber strain of simply supported beam specimens subjected to third-point loadings, which
produces uniaxial bending stresses, is calculated from
t = specimen depth, millimeters (inches)
d = dynamic deflection of beam center, millimeters (inches)
L = reaction span length, millimeters (inches)
a = L/3, millimeters (inches)
c. Test Equipment.
(1) The repeated flexure apparatus is shown in Figure M-1. It accommodates beam
specimens 381 millimeters (15 inches) long with widths and depths not exceeding 76 millimeters
(3 inches). A 1,361-kilogram- (3,000-pound-) capacity electrohydraulic testing machine capable of
applying repeated tension-compression loads in the form of haversine waves for 0.1-second
durations with 0.4-second rest periods is used for flexural fatigue tests. Any dynamic testing
machine or pneumatic pressure system with similar loading capabilities is also suitable. Third-point
loading, i.e., loads applied at distances of L/3 from the reaction points, produces an approximately
constant bending moment over the center 102 millimeters (4 inches) of a 381-millimeter- (15-inch-)
long beam specimen with widths and depths not exceeding 76 millimeters (3 inches). A sufficient
load, approximately 10 percent of the load deflecting the beam upward, is applied in the opposite