In view of the fact that prestressed concrete is extensively
used in bridge construction and that it holds potentialities for eventual use in pavement construction, and that
methods must be investigated to utilize an otherwise rejected
aggregate which cannot be used for its poor performance under
natural weathering, it has become of paramount importance
that further efforts be made to evaluate the effect of prestressing
on the durability of concrete.
The purpose of this thesis was twofold: 1) To study the
durability of prestressed concrete made of poor-performing
aggregate; 2) To compare the freezing and thawing effects on
prestressed concrete with those on ordinary concrete.
Two mix designs having different proportions of poor
performing aggregate were used in this study. Half the number
of specimens were post-tensioned after they had been
cured for a period of 13 to 18 days in water, and were then
replaced in the curing room for 24 hours, Level of prestress
was 600 psi. Before transferring the specimens - both prestressed
and non-prestressed - into freezing and thawing
apparatus, they were tested for fundamental transverse frequency
and initial weight and length measurements were recorded.
Thereafter, transverse frequency, weight, length
change and temperature change measurements were made periodically. The relative dynamic modules of elasticity and durability factor were then calculated for each specimen.
On the basis of the results furnished by these tests,
it may be concluded that prestressing improves the durability
of concrete made of poor performing aggregate and that the
magnitude of improvement in the durability ef concrete tends
to diminish with increasing proportion of good performing
aggregate.
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