Visualize an Oreo cookie with two hard layers sandwiched around a soft inside. That is exactly what the Target and Ace Hardware distribution centers would have looked like if they had simply densified their carbonated floors when they started failing.
And if they did nothing, it would have been as though they had taken off the top layer. This would have resulted in just soft concrete over hard.
Instead, both companies, three years apart, had the good fortune to have come in contact with Jason Bye, the local representative for the RetroPlate Concrete Polishing System. After analyzing the floor, Bye and the RetroPlate certified applicators provided a permanent fix, utilizing grinding equipment from Innovatech, diamonds from RetroPlate and Innovatech, and the Retro-Plate densifier.
A team effort brought together experts in concrete surface polishing. Instead of failing floors or a short-term fix of solely densifying, Target and Ace Hardware have received long-term, permanent solutions.
Defining the problem
The first step in finding a solution was to determine the problem and what caused it. Only then could a solution be developed. As a basis for our discussion, consider the following:
- Carbonization – This is a reaction which occurs when curing concrete is exposed to CO2 exhaust from propane-powered construction equipment and heaters. The exhaust drops to the floor surface in enclosed construction sites that lack adequate airflow exhausting to the outside. CO2 has a very low solubility in water, and when this occurs in conjunction with newly finished concrete, it will interact with the cement paste as it is curing. Hydration is impeded and the surface area will dry out. This creates a porous and weak floor, without reaching its normal strength and performance. Carbonization occurs primarily during colder climate pours. (The reaction is CO2 + Ca (OH2) = CaCO3 (+H2O).)
- Densification – This is the chemical reaction which creates crystallization within the concrete when a silicate or siliconate interacts with the calcium hydroxide that is created during the hydration of cement during curing. Densifiers can be sodium silicate-based or a siliconate. Sodium-based densifiers are most common. There are also lithium and potassium-based densifiers.
- Grinding /Polishing – This involves utilizing three- and four-headed industrial planetary grinding machines, initially adapted from stone and terrazzo finishing. This reduces laitance, removes coatings and weather damage, and produces a tightly closed floor surface in conjunction with a densification chemical. The equipment utilizes industrial diamonds in metal, phenolic, or resin bases. Each diamond has a different grit. A lower number indicates a larger grit. Generally, grits through 400 are considered grinding steps where significant stock removal occurs. Grits above 400 are polishing stages.
Almost 10 years ago, Kmart built a new 1 million-square-foot distribution center in Amsterdam, N.Y. But Kmart never used the facility, and six years later, Target bought the site and added another 400,000 square feet.
During the expansion early this year, the general contractor, Archer Western, was experiencing dusting in the original portion of the facility. This was very similar to what happened at Ace Hardware's nearby 557,000-square-foot facility.
Archer Western contacted Bye, a representative for RetroPlate Concrete Polishing System of Springville, Utah. Bye had been involved with the Ace Hardware project, so he was able educate Target officials on what he perceived to be the problem, and consequently, how to fix their warehouse. Bye introduced the managers from both companies to each other. So Target managers were able to evaluate a site that had similar problems, three years after repairs had been completed.
Like Ace, Target performed third-party core sample testing to confirm the carbonated flooring condition. The depth of carbonation ranged from ¼ to ¾ inches deep. Surface Tech, a RetroPlate certified applicator, then performed a test sample for Target to analyze. Ideally, the process was not just going to deliver a strengthened floor, but it was also was going to allow Target to lower maintenance costs and reduce air filter costs.
A key factor which Rob Simon and Mark Clasen of Surface Tech recommended was that when ground dry, there would be minimal disruption to the facility's operations. Surface Tech, behind seven Innovatech Predators and vacuum systems, uses a range of diamonds that start at 40-60 metals, running through 100 metals, 200 metals, application of the RetroPlate, and continuing on through 220 resin, 400 resin, and 800 resin.
Lines of communication
The project began in July 2006, with Target predetermining the layout for the project and taking into account work areas. It is very important that Surface Tech maintain open channels of communications and that they do not interfere with critical product placement periods.
When staging the work, it was imperative to plan for equipment needs: grinders, diamonds, vacuums, power sources, dumpsters for disposal, adequate trained personnel, and guaranteeing proper lighting.
Open areas that receive traffic were the actual locations to be repaired. Initially, the work is being released in 35,000-square-foot areas. Work is performed Tuesday through Sunday, from 7 a.m. to 9 p.m. About 2/3 of the 1 million square feet will receive the complete RetroPlate System of grinding, densifying and polishing; the remaining areas under the racking will receive RetroPlate densifier only. These areas do not receive traffic, and the Retro-Plate densifier will minimize the degradation and dusting in these areas.
Concrete contractors must provide proper airflow while pouring and curing a new slab. Refreshing the air at an adequate flow rate will eliminate this costly error. Carbonization is more likely to occur in colder climates on new concrete pours, but has also occurred on existing floors where all the conditions are right (or wrong)—poor ventilation, and excess CO2 and moisture. Without moisture, the CO2 will not penetrate and interact with the concrete.
Target has found the long-term solution for an unfortunate and unnecessary problem.