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Overcoming Obstacles to Achieve Results

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Gallatin Steel, located in Ghent, Ky., is a steel mini-mill manufacturer of numerous hot rolled steel coil products and aluminum, zinc, brass, bronze and lead coiled products, producing 1.4 million tons of coils annually. The products are derived from scrap materials melted in direct-current (DC) electric arc furnaces. Recently, two of the furnaces needed replacement and Gallatin Steel wanted to know the condition of the concrete they were supported on.

Terracon was selected to evaluate the condition of the pedestal concrete walls as part of the furnace replacement project. Failure or weakening of these pedestal walls could pose serious issues with both personnel safety and iron production.

The 20-foot-tall concrete pedestals are subjected to significant weight bearing furnace components, extreme temperatures, and furnace releases of molten and sulfur-bearing slag as part of the iron ore smelting process. Vertical pedestal walls have been protected over the years by several applications of gunite/shotcrete to an unknown thickness, which were observed to be delaminating from the pedestal walls in most locations.

Terracon’s first task in this investigation was to develop a testing program to evaluate how the pedestals held up with the extreme circumstances.

The testing program consisted of compressive strength testing, petrographic examination, and chemical testing for water extractable sulfate content. In order to evaluate the physical properties of the concrete, Terracon utilized a diamond-tipped core barrel and core drill to obtain four-inch diameter cores from the walls. The core drill had to be mounted and secured to the wall face using expansion anchors to hold it in place during drilling.

For the Terracon team, this project was unique in the complicated coordination that had to take place both from a Terracon and client standpoint. The coring process presented several obstacles the team had to work to overcome.

The coring operations were logistically challenging, requiring the use of a man-lift to access the upper portions of the pedestals, which were as high as 20 feet above the ground. Terracon personnel were required to work during restricted hours, so the team had to work quickly and efficiently.

In fact, all of the field coring activities had to occur within a designated “shut down” period, which was only two days. Terracon was authorized to perform this work only three business days before the planned shut down. It was critical to complete the field activities during this time to avoid delay since the next shut down was not scheduled for at least another 30 days.

To complicate matters, Gallatin Steel needed to periodically start up these furnaces during the shut down period, which further delayed the coring operations. The brief start-ups also posed a physical hazard to the coring crew, as these operations resulted in releases of cooled slag and metal fragments from a discharge chute at the bottom of each furnace. Numerous false starts were encountered, in which the core drill barrel siezed up trying to drill through hardened steel slag or hitting an embedded reinforcing steel bar. Overall, 12 attempts were made to extract cores in order to get the seven needed for testing.

With quick yet thorough planning, Terracon was able to successfully perform the activities within the allotted time period and obtain the total number of cores for testing.

The seven cores were returned to Terracon’s Cincinnati materials laboratory for testing. Each core was visually examined for physical characteristics, and three of the cores were subjected to petrographic examination by Terracon Petrographer Terry Stransky, P.G. Compressive strength tests were performed on six of the cores, and water-extractable sulfates were performed on all seven cores to identify chemical effects from sulfur-bearing slag.

Test program results indicated that, while limited fracturing of concrete from the pedestals was apparent, the fracturing had not resulted from heat stress or chemical attack from external sulfate exposure. There was no evidence of chemical (sulfate) attack of the concrete. In fact, the concrete consisted of a very well hydrated, adequately consolidated, Portland cement and fly ash, air-entrained concrete. Terracon was able to determine for Gallatin Steel the concrete was in good condition.

However, the gunite/shotcrete overlays, while protecting the underlying pedestal concrete from the heat and chemical effects of the steel slag, appeared to be in poor shape. Terracon recommended the removal and replacement of these materials.

Bringing both sides, the owner and consultant, of the project team together safely and successfully was the result of solid client relationships and people from both teams were willing to work together to accomplish a common goal.