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.
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."