TM 5-809-3/NAVFAC DM-2.9/AFM 88-3, Chap. 3
CHAPTER 10
NONDESTRUCTIVE EVALUATION TECHNIQUES
10-1. Introduction. This chapter provides non-
evaluation studies. Each technique must be used to
destructive evaluation (NDE) techniques for ma-
its best advantage in combination with others to
sonry in existing buildings. Techniques for both the
develop a body of evidence upon which
evaluation of the condition of the materials and the
conclusions and decisions may be made regarding
determination of material properties are included.
existing conditions and rehabilitation measures
required for masonry structures. Table 10-1 lists
Traditional
evaluation
each NDE technique along the top and gives the
10-2. Background.
methods for the condition and properties of ma-
desired information along the left side, which are
sonry features of buildings have been, in addition to
grouped under the headings of material properties
visual inspection, destructive testing of specimens
and condition. A simple matrix of dots indicates
removed from the structure. Destructive methods
which techniques are useful for measuring each of
of evaluation are inherently limited because
the desired quantities. A filled dot indicates the
specimen removal may be aesthetically and
technique is useful while an unfilled dot indicates
structurally damaging. Further, because of the
that the technique is useful, but may be affected by
potentially structurally destructive nature of these
conditions such as loading and crack distributions
methods and the facts that they can be relatively
in the walls. Thus, the techniques with unfilled dots
expensive and aesthetically unpleasant, the number
should be used in tandem with others to strengthen
of specimens taken may be limited to a small
the reliability of the results.
number. Thus, potentially, the quantity and quality
of the resulting data may be poor and/or
10-5. NDE Tests.
a. Schmidt Hammer. The Schmidt Hammer test
inconsistent.
is the quickest, simplest, and least expensive
10-3. NDE methods. The use of NDE techniques
method for NDE of solid clay unit, i.e., brick
can provide the structural engineer, who is charged
masonry. As shown in figure 10-1, studies show a
with evaluating the structural integrity and
reasonably good correlation between the rebound
serviceability of the masonry features of an existing
number and the compressive strength of clay brick
structure, invaluable information. NDE methods
masonry.
can be used in conjunction either with each other or
The Schmidt Hammer is most ideally suited to the
with destructive methods. The NDE methods
measurement of material uniformity over large
described herein are those which offer the greatest
areas of a structure. It must be accompanied by a
potential at the present time for determining the
limited number of destructive tests to calibrate the
location of flaws within masonry members and for
results if an indication of the actual masonry
assessing masonry materials properties.
strength is required. The simplicity of the test is
offset by its limited utility. Its use is suggested only
for determination of the uniformity of properties
10-4. Application of Combined Techniques.
Combined NDE techniques. It is apparent that, of
over a large area of a structure.
(1) Equipment. The Schmidt Hammer is a
the methods described here, no single technique
will be sufficient for "complete" nondestructive
compact, lightweight instrument that provides a
evaluation of masonry, where the term "complete"
measure of relative material surface hardness. It has
means comprehensive evaluation of both condition
been used extensively in the testing of concrete and
and quality. The mechanical tests, such as the
rock. The hammer consists of a spring loaded
flatjack, and in-place shear test, provide data
plunger which, when released, strikes a surface and
directly related to quality, and perhaps indirectly a
causes a mass within the hammer to rebound. The
measure of condition. Conversely, impact and
magnitude of the rebound is indicated on a scale at
stress wave techniques evaluate condition and
the "rebound number". This number gives an
indirectly measure quality. Furthermore, the results
indication of surface hardness which can be
from the latter techniques are often difficult to
correlated to the strength or condition of the
interpret in the absence of information about the
material. For the evaluation of solid clay (brick)
state of stress that can be provided by the flatjack
masonry units, the hammer is pressed against the
test. At the present time, therefore, the scenario for
center of the vertical surface of an individual brick
utilization of NDE techniques calls for use of two
in a wall. The rebound number is a function of the
or more complimentary techniques for most
brick hardness and the mortar in which the brick is
10-1
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