UFC 3-260-03

15 Apr 01

stresses created by the load reaction will not influence the results of the plate-bearing tests. In general,

the load reactions should be located on slabs adjacent to the slab on which the test is being performed

and not less than 3.8 meters (12.5 feet) from the bearing plate. When the plate-bearing tests are per-

formed on the surface on a pavement, the limitation outlined in chapter 3 of this manual will apply.

B-5. MOISTURE-DENSITY-CBR RELATIONS. The moisture-density-CBR relationships of the founda-

tion materials may be required to evaluate a nonrigid overlay on rigid pavement and this should be

developed as outlined in TI 825-01/AFM 32-1124 (I)/NAVFAC DM 21.10.

B-6. FLEXURAL STRENGTH TEST. The flexural strength of the rigid pavement will be determined by

the third-point loading procedure set forth in ASTM C 78 with the following modifications.

a. Test Specimens. For pavement thicknesses up to and including 305 millimeters (12 inches), the

test specimens should have a square section with the width and thickness equal to the pavement thick-

ness. For thicker pavement, either a square section with width and thickness equal to the pavement

thickness can be used, or 152- by 152-millimeter (6- by 6-inch) beams can be cut from the top and bot-

tom of the slab and tested with the results averaged to obtain a strength representative of the full sec-

tion. With the 152- by 152-millimeter (6- by 6-inch) beams cut from the top and bottom of the slab, the

slab required from the pavement may be much smaller than that required when the width and thickness

of the specimen must equal the pavement thickness. The length of the specimen should be three times

the thickness of the specimen plus approximately 152 millimeters (6 inches).

b. Procedure. The specimen shall be placed in the third-point loading apparatus and tested in its

as-cast position. That is, the load shall be applied at the third points on the surface of the beam, which

represents the pavement surface, and the load reaction will be located on the bottom of the beam, which

represents the bottom of the pavement.

B-7. SPLITTING TENSILE STRENGTH TESTS. The splitting tensile strength test has been standard-

ized by American Society Testing and Materials (ASTM). The procedures for conducting the test and

calculating the splitting tensile strength of concrete cores are outlined in ASTM C 496. Essentially, the

method consists of laying a concrete core with its longitudinal axis horizontal and then loading it along

the longitudinal axis with a line load until the core splits along its diameter. The splitting tensile strength

T is then computed from the equation:

2*P*

(eq B-1)

π*ld*

where

P = maximum load at rupture, Newtons (pounds-force)

l = length of core, millimeters (inches)

d = diameter of core, millimeters (inches)

A correlation should be established between the splitting tensile strength from 152-millimeter- (6-inch-)

diameter cores and the beam flexural strength for each pavement where records indicate there is a

difference in the properties of the concrete. If it is not possible to obtain samples for flexural beam tests,

splitting tensile strengths for 152-millimeter (6-inch)-diameter cores can be used with the following equa-

tion to obtain values of flexural strength for use in the evaluation. For 6-inch-diameter cores:

B-3