Producing rapid-setting cement for use in cold regions is a
challenge in the cement industry. Conventional portland cement, an invention of
the 19th century, has limitations in its use on roads and bridges in cold
climates. For example, road repairs are often done by first filling the
potholes temporarily in the winter with asphalt and making the final repair
with portland cement in the spring.
In permafrost regions such as Alaska and northern Canada,
because of long winters any cementing job is a great challenge. The industry
involved with oil-field drilling and borehole completion faces a similar
problem in the Arctic region. The performance of cementing jobs without
disturbing the permafrost region surrounding the drilling area is problematic
because conventional cements neither set well nor sufficiently insulate the
surrounding ice formation when hot crude flows through the boreholes. Even pipeline
supports in Arctic climates need insulating cement to avoid thawing of the
supporting ground due to hot oil flowing in the pipes.
Portland cement-based variations are currently in use for
most of these applications, but these cements have the same calcium
silicate-related chemistry as used for warmer climates, and hence their basic
properties such as setting characteristics and thermal properties do not change
much. Thus, a novel cementing solution is needed to address the specific
problems related to cold climate applications.
During the last 10 years, Argonne National Laboratory,
Argonne, Ill., has been developing
Ceramicrete, a phosphate-based cement that may provide a solution to these cold
climate problems. This cement was originally developed for encapsulating
nuclear waste, and now is becoming a sensible option for DOTs across the
midwest and northern U.S. Illinois, Wisconsin, Indiana, Minnesota and
Pennsylvania are just a few states that now use a byproduct of Ceramicrete for
road and bridge repair.
Road life
The Ceramicrete binder consists of a blend of calcined
magnesium oxide and monopotassium phosphate. The blend is mixed with a small
amount of water. The reaction product, a rapid-setting phosphate binder, is
Ceramicrete. The binder by itself is not a very useful material because it has
nearly the same strength as that of portland cement and is comparatively
expensive (30 cents per lb against 4 cents per lb for portland cement).
However, a small amount of the binder when mixed with coal or any other ash in
a large proportion enhances its strength by two or three times. The cost then
becomes low enough that the material is suitable for specialized applications
such as cementing jobs in cold regions. For example, for road-based
applications the ideal composition of the mix is one where binder is only 25
wt% of the total. This brings down the cost of the mix to less than 10 cents
per lb. The slurry from the mixture of the binder and the ash is free-flowing
and self-leveling, and once poured in potholes it generates its own heat by
chemical reactions. The slurry sets within hours and seals the pothole tightly,
and the road is ready for the next day's traffic.
In March 1999 at Argonne, two road patches were repaired
with Ceramicrete on a trial basis to fill potholes on a road with heavy traffic
from delivery trucks. The debris from the patches was not cleared, nor were the
sides cut into smoother shapes. The temperature was 40°F. A few hours after
the repair it rained heavily and the patches, which were in low-lying areas,
were under water until the next day. In spite of the water exposure, the
patches set well. Not only have they withstood traffic for the last three
years, but the freeze-thaw cycles of the three winters have not caused any
damage.
Finding its place and staying there
In 1997, Ceramicrete was licensed to Bindan Corp., Oak
Brook, Ill., and President Tom Lally subjected himself to a crash course in
phosphate cements.
"I started reading every book in the world," he
told Roads & Bridges. "Books on phosphate bonding, acid base reactions
and basic cement technologies."
The education led to experimentation. Bindan Corp. made up
samples of the patching product and began running tests, which lasted about a
year.
The American Association of State Highway &
Transportation Officials (AASHTO) also put the product--Bindan Corp.'s version
is called Mono-Patch--through a series of trials. Their results showed that the
product was a rapid-setting cement and its 28-day strength (10,202 psi) was
very high. AASHTO's test showed Ceramicrete reaching a compressive strength of
2,055 psi in just six hours, 8,046 psi in 24 hours and 8,613 psi in seven days.
The shear bond strength results also were impressive--7,196 psi
in 24 hours. Following the AASHTO testing 15 states conducted their own
independent tests and placed the Ceramicrete product on their approval list.
The strength numbers are impressive, but ideally Lally
wanted the product to be simple.
"The premise I started with was the idea that if I can
do it, anyone can do it," he said.
Lally also had the ambition to make it happen. He showed up
at the doorstep of the Illinois State Toll Highway Authority and requested the
worst-case scenario for his patching product.
"They told us they were looking for something that
stayed in place," Lally said. "Initially out of the box there was no
distributor for this product. We had to go to people directly. After seeing the
product, the Tollway started bidding jobs with it."
The good word traveled to the Chicago Skyway, which began
using the product on its toll bridge, and the Illinois Department of
Transportation.
USG Corp., a Bindan competitor, was intrigued and invited
Lally to come down to its Chicago headquarters. USG Corp. ran more tests at its
laboratory in Libertyville, Ill., and the two companies formed a partnership to
market Mono-Patch.
"After all the testing they came back to me and said,
?What you're saying (about Mono-Patch) is true,'" recalled Lally.
The Mono-Patch mix, which consists of a phosphate binder,
sand and small aggregate, comes in a ready-to-use 50-lb bag. After a pothole
has been identified, crews come in and saw off a square section. All concrete
in the damaged area is broken up as far down as the rebar.
"Some will go down to the first rebar, but some will
not," said Lally. "It really depends on the depth of fill."
The space is then cleaned and any soft spots are treated.
The next step is critical. According to Lally, a high mixing energy is needed
with Mono-Patch and water (about 10% of content). A mortar mixer is
recommended, but a 5-gal bucket with paddle inserts also could be used. When
the mix is ready it's poured into the section and crews usually run a 2 x 4
piece of wood back and forth to level it off.
"This product is very sticky and gooey, so you don't
want to necessarily trowel it," said Lally. "They're not looking for
the perfect finish. They just want it to stay in place.
"Another advantage we have over other phosphate cements
out there is we don't set as fast. That's due to the acidic part of the formula
we're using . . . it's more controllable. That's very much like normal
cement."
