APPENDIX B: SHRINKAGE MEASUREMENTS
A major weakness of concrete is that it shrinks
with age, and much of this shrinkage is due to
moisture loss. Inadequate allowance for the
effects of shrinkage can lead to cracking, warping
and twisting, all of which reduce the service life
of concrete. We measured the shrinkage of con-
crete as a function of moisture content. However,
we did not use a sealed specimen as a control.
Thus our shrinkage measurements are due to two
causes: moisture loss due to drying (evaporation
to the atmosphere) and moisture loss due to self-
desiccation (water consumed by hydration).
The samples used for this test were made with
the same mixture proportions and materials used
for the TDR specimens made with the larger
coarse aggregate in Part II (see Tables 2 and 3).
The samples were molded into 7.62- 7.62-
28.58-cm beams fitted with stainless steel gage
studs in their ends. Measurements were taken
according to ASTM C 490 each time the specimen
was partially dried. The drying procedure de-
scribed for the TDR samples was followed here.
Figure B1 shows an individual shrinkage meas-
Figure B1. Extensometer used to measure length at
urement being taken.
the centerline of the concrete.
Current practices acknowledge that concrete
will crack, and accommodate for this eventuality
property that is modified by coarse aggregate.
by making it crack at strategically located joints.
Thus, the study should investigate the effects of
Concrete can be designed to shrink less but little
cement content, water content, and aggregate
information is available on how to do this. A sys-
shape, size, and type on shrinkage. Also, certain
tematic study is needed to define the shrinkage
chemicals admixtures can influence shrinkage in
characteristics of concrete. Drying-shrinkage of
a positive way. These should be investigated as
concrete (see Fig. B2) is largely a cement paste
well.
Figure B2. Shrinkage vs. water content of concrete.
15
Previous Page
