The terminal floor at the Ted Stevens Anchorage International Airport was a 20,000-square-foot, 40-year-old concrete slab that had seen a variety of floor coverings over the years, including tile and most recently carpet. The floor experienced moisture issues, and the carpet made the terminal look dark and out of date.
The design team in charge of the terminal remodel wanted a flooring option that would brighten the space and bring the facility into the modern age. Polished concrete was appealing for its ability to satisfy those needs, but it was polished concrete's low maintenance requirements that really caught the design team's attention.
Steve Rose, owner of Grand Prospect Corporation, a concrete polishing contractor out of Big Lake, Alaska, was brought on to consult the airport job for eight months. He answered the design team's questions about polished concrete, produced mock-ups, speculated on the condition of the concrete under the carpet and explained possible repair options since they didn't know what kind of cracks and spalling they might run into once the carpet was removed.
In the end, the airport design team decided polished concrete would be the ideal flooring option for its terminal remodel and hired Grand Prospect for the job.
Not just hard, but really hard
The Grand Prospect crew started the airport terminal job by removing the existing floor coverings and utilizing a ride-on grinder to remove old adhesives. Once the crew uncovered the slab, it found the floor wasn't as damaged as they thought it would be and were able to proceed with typical repair methods.
"One major issue we had with the floor was the flatness -- you could see the floor waving, or undulating, which we knew would present a few problems in catching those lows and highs when grinding," Rose explains.
With the floor open, repaired and ready for the polishing process, the Grand Prospect crew stumbled upon another surprise. "The floor was poured in a couple different phases. When we started in the middle it was hard, but we were using regular diamonds and having success," Rose says. "But it seemed every time we would cross over a joint line the slab would change, and the concrete was getting harder."
When Rose started scratching around the floor with a Mohs hardness test kit, he found in many places the concrete was a 9 on a hardness scale of 1-10 (10 being the hardest). "Of course that presented difficulties in getting the proper tooling," Rose explains.
Generally speaking, Rose says you want to have your diamonds set in a soft resin bond when you are grinding hard concrete. "If you use a hard bond on a hard floor, the diamonds would just glaze over the floor. That hard carrier wouldn't wear down fast enough to expose your diamonds and the process would be ineffective," he explains.
Grand Prospect worked with its abrasives supplier to get a variety of options shipped in so the crew could test for the most effective tooling. Rose found a super-soft diamond metal-bonded double wing round cutter in 30/40 grit that worked for the initial cut on the really hard sections of the slab. Grand Prospect's second grinding step on the hardest sections of the slab employed a Trojan double weight extra soft metal bond cutter from Diamatic in a 60/80 grit. On the sections of the floor that weren't so hard, the Grand Prospect crew was able to use a metal-bond abrasive with 30/40 grit followed by a 3-inch ceramic transitional abrasive.
Another conundrum Rose faced was the inability to do a full wet grind but somehow cool his diamonds on the super hard concrete. His solution was something in between a wet and dry grind. "We used a misting system," he explains. "We had one worker misting water in front of the machine with a pump sprayer, applying no more than would evaporate from the diamond use. It gave us some of the advantages of wet grinding without the slurry."