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Planning Plays Key Role on Slab Removal Job in Toledo

Mon May 09, 2005 - Midwest Edition
Construction Equipment Guide

The Windermere Pumping Station in North Toledo, OH, is one of four main pumping stations in the greater Toledo area. Constructed in 1982, the facility recently needed to replace all of its major pumping equipment. The upgrades required cutting and removing a 12-in. (30.5 cm) -thick structural slab measuring 35 ft. (10.7 m) long and 20 ft. (6 m) wide.

In July 2004, CSDA member Ohio Concrete Sawing & Drilling Inc. in Sylvania was contracted by Mosser Construction Inc. in Toledo to saw and remove a 12-inch-thick concrete floor slab that was attached to the exterior of a building that was being occupied. The removal would expose the basement area under the slab, allowing access to the basement for the equipment upgrades.

The 35-ft.-long by 20-ft.-wide slab was located directly above a double basement and shoring was not feasible because there were weight restrictions of 150 lbs. per sq. ft. on the first basement floor.

Mosser specified concrete cutting because it would be precise, leaving the remaining floor and building undisturbed and clean. The general contractor specifies quite a bit of sawing and drilling, especially in its bridge work, and knew it would be the most appropriate method for this job. The slab could be lifted out of the way by a crane that would work from the parking lot, thereby eliminating the problem of access.

Removal of the precisely cut slab of concrete by crane would also reduce the risk of anything falling and damaging the basement floor 18 ft. below. It was also a time-saving method as cutting would progress quickly and cleanup would be held to a minimum. A crane would be required for lifting the cut pieces, but this would take less than eight hours including travel time from the crane yard and back.

Prior to cutting, the general contractor excavated the asphalt pavement surrounding the slab so operators would have room to perform the cutting work. When Ohio Concrete crews arrived on the job with two operators and two trucks, they began flush cutting and wall sawing simultaneously. Operators used a 35-hp (26 kW) Cushion Cut wall saw from Dimas to make a 28-ft. (8.5 m) flush cut in the slab along the building and to cut the three exposed sides of the slab’s perimeter, freeing the 12-in.-thick slab from the supporting walls.

Next, operators drilled 24 holes for rigging and removing the slab. Ohio Concrete’s crew carefully laid out and drilled core holes that would be used for lifting the 67,000 lbs. (30,391 kg) piece of concrete. The holes were laid out so they could be used for lifting the large piece as well as the smaller pieces resulting from the main slab’s division into smaller sections. Operators would need these holes to be placed correctly in order to rig the pieces using the basket lift method, a secure form of lifting in which all four corners of the slab are rigged.

Operators then began flat sawing to cut the dogleg area of the slab. The main slab was now a rectangle weighing 67,000 lbs. There were a couple small areas in corners of the main slab near a step that required some chain sawing to free the slab for lifting. When completely cut, this large piece was removed using a 100-ton crane and set on 4 by 4-in. (10 by 10 cm) pieces of wood in the parking lot next to the crane.

With the large slab placed securely in the parking lot, operators used a Core Cut 6500 gas-powered flat saw from Diamond Products to make three 18-ft. (5.5 m) cuts, reducing the large piece into four smaller pieces for removal. Cutting the slab before it was lifted was not an option as it was resting on only three walls. This operation would have required major shoring from the sub-basement floor and the floor below the slab, a method that would have been too labor intensive. This method would have also created safety issues in moving materials in and out of the basement. So by cutting the large slab from the parking lot, operators were able to quickly reduce the slab into four manageable pieces. On the last day of the job, the crane arrived and each piece was loaded into a 20-yd. dumpster for disposal. Work was completed by early afternoon.

All lifts were made with a basket lift using straps and a clevis, the fastening device, to attach to the crane cable. A 100-ton crane was used so all the dumpsters could be reached without moving the crane. Five 20-yd. dumpsters had been ordered while cutting was still in progress to assure timely delivery. The dumpsters were positioned in the lot so the crane could reach all of them without relocating.

The job was completed ahead of schedule, largely because operators did not have to make any more cuts than necessary to get the pieces to the dumpster.

“I appreciate the way Ohio Concrete personnel took time to think through this project to make sure all the needed equipment was on hand,” said Mike Rettenberger, the job superintendent of Mosser Construction, of Ohio Concrete’s performance on this project. “This allowed them to complete the project in a short period of time and without any interruptions to our work or other activities at the pump station.”

The biggest concern on this job was that other contracted employees were working near the rigging and removal area. The Ohio Concrete crew had to ensure that these employees remained clear of the work, especially during the lifting. Ohio Concrete used standard caution tape around the excavation area and notified other contractors in the area about the planned lift of the slab.

Safety was never compromised during the job. Operators wore all the required Personal Protective Equipment (PPE) including hard hats, safety glasses and ear protection. All lifts were completed using the basket method, meaning the concrete pieces were supported on all four corners, not only two, which could have caused the piece to flip during the lifting.

In all, Ohio Concrete operators performed 28 ft. (8.5 m) of flush cutting along the building; 76 ft. (23 m) of 18-in.-thick wall sawing to free the slab from the walls; 24 ft. (7.3 m) of flat sawing on the slab in place to remove the dogleg; and an additional 60 ft. (18.3 m) of flat sawing to further break down the slab for placement in the dumpsters after the cut slab was set in the parking lot. Twenty-four 5-in.-diameter holes were core drilled through the slab for lifting.

“The job stayed on schedule and the customer was very satisfied with the work and the housekeeping,” said John Aston of Ohio Concrete Sawing and Drilling.

While the job may not appear that complicated, Ohio Concrete’s pre-planning efforts, cutting strategy and attention to details such as the timing of equipment arrival and the size of the crane ordered all contributed to the smooth, timely completion of the job.

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(This story appears courtesy of CSDA and Concrete Openings magazine.)

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