The
primary objective of this project was to complete a systematic
assessment of concrete bridge deck and crack sealers based on
their effectiveness and life performance. Deck sealers are commonly
applied during the final stages of construction to protect the
deck against chloride ion intrusion. Crack sealers are used to
penetrate, fill, and bond existing cracks back together. While
both types of products are commonly used by Departments of Transportation
around the country, little is known about the effectiveness of
the products over time.
The deck sealer portion of the project focused on measuring the
ability of 14 different deck sealers to resist chloride ion intrusion
from a deicer solution typically used on Wisconsin bridges. Several
batches of concrete were cast, each containing 10 concrete prisms
measuring 3"x11"x11." Twenty-one days after casting
the concrete, the top 11"x11" surface of six specimens
from each batch were sealed with a concrete bridge deck sealer
currently available to and possibly in use by the Wisconsin DOT.
The remaining four specimens from each batch were left with their
top surfaces unsealed to serve as controls. A week after sealing,
the top surface of each specimen was sandblasted, removing approximately
1/8" of the top concrete surface to simulate abrasion that
would occur on bridge decks due to vehicular traffic. The specimens
were then allowed to dry out for 14 days, during which time a
foam dam was built around the outside perimeter of the top of
the specimens.
After the drying period, all six of the sealed specimens and three
of the unsealed specimens from each batch began 90 days of continuous
ponding of a deicer solution, 3% sodium chloride. While some specimens
were left to be ponded at ambient conditions in the Wisconsin
Structures and Materials Testing Laboratory, companion specimens
for each sealer were ponded while subjected to freezing and thawing
cycles. The cycles, intended to simulate Wisconsin winters, were
performed in a temperature controlled room at the University of
Wisconsin Biotron, where one cycle of freezing at -4°F alternating
with thawing at 86°F was performed each day.
At
the conclusion of ponding, all specimens were rinsed of the remaining
deicer solution and allowed to air dry. Three samples were drilled
from each specimen, taken from a depth of 0.5" to 1"
below the top surface. These samples were tested using a titration
procedure to determine the percent of chloride they contained.
The sealed samples were compared to the unsealed samples from
each batch to measure the relative performance of the sealers,
where the lower percent chloride ion indicated a sealer was better
able to penetrate and protect the concrete. In addition, chloride
ion tests from the specimens subjected to freezing and thawing
cycles were used to gauge the decreased ability of the sealer
to protect the concrete due to freezing and thawing.
The second area of this project focused on testing concrete crack
sealers on their depth of penetration and bond strength and durability.
Concrete prisms measuring 3"x4"x16" were cast,
cut in half lengthwise, and cracked lengthwise through the center.
The cracked pieces were then repositioned using aluminum foil
as a shim to create a crack of a desired width. Crack sealers
were
then applied to the cracked pieces to rebond them. After applying
the sealers, some specimens underwent a depth of penetration test,
in which the sealed specimens were sliced through their thickness,
and the maximum depth of penetration of the sealer was measured.
Another set of specimens were tested to determine the bond strength
of the sealer to the concrete. A companion set of specimens were
subjected to 300 freezing
Photo 2. Crack sealer specimen ready to be sealed
and thawing cycles, where the temperature
of the
specimens was alternately lowered to 0°F and raised to 50°C
in a period of five hours. At the conclusion of the freeze thaw
cycles these specimens were also tested for bond strength to determine
the durability of the sealer to remain bonded to the concrete
while experiencing freezing and thawing cycles.
