Sweeping the Board

GPR Imaging and Diamond Tools a Winning Combination

The use of non-intrusive ground penetrating radar (GPR) technology provided a Chicago-based CSDA member with critical data to flat saw over 2,000 linear feet of concrete safely and accurately in one of the city’s most iconic buildings.

Crosby Associates is a planning and design firm of visual identity, branding and communications programs for organizations, products, services, events and initiatives. The firm’s office is located on the 35th floor of the 605-foot-tall, 44-story Chicago Board of Trade Building.

A GPR imaging technician scanned over 400 square feet of concrete flooring.

A GPR imaging technician scanned over 400 square feet of concrete flooring.

When the company decided to renovate its 3,400-square-foot office space, it was specified that all electrical cabling be out of sight and buried for safety and aesthetics. Therefore, a 200-linearfoot trench 24 inches wide, along with various other cuts, was to be made in the concrete office floor to bury cables and accommodate new furniture and fittings. The trench had to be 2.13 inches deep with a 0.06 tolerance for both depth and width. It would be covered by a cushioned cork material for employee comfort upon completion. However, the floor contained hidden keyways and other objects connected to the building’s architecture, utilities and office space below. Therefore, each of these objects had to be located, identified and avoided before cutting and chipping out the concrete. It was made clear by the owners that there was no margin for error.

The trench depth tolerance was based on the existence of a clay tile floor underneath the concrete. This clay floor could not be disturbed, as per the specification of the Chicago Board of Trade, because the keyways that locked the tiles in place also helped maintain structural integrity. In addition, a banking firm occupied the floor below and would remain in operation during the work, so noise and water control while cutting was crucial. The general contractor for the renovations, H&R Johnson Bros. Inc. of Evergreen, Illinois, worked with electrical contractor Brennan Electric, Inc., also of Evergreen, and chose Chicago Cut Concrete Cutting of Schaumburg, Illinois to cut the trench and other areas.

“We were referred to Brennan Electric for this project based on our reputation in the Chicago Board of Trade Building. We had successfully completed numerous projects in the building before this one, so were confident that this job would have a positive outcome,” said Tiffany Phillips, owner of Chicago Cut.

Operators created a trench that was 24 inches wide and 2.13 inches deep to house electrical cabling.

Operators created a trench that was
24 inches wide and 2.13 inches deep to house electrical cabling.

No other methods were suitable for the job. It was not only essential that the contractor acquired data to show all hidden objects below the surface, but also that operators used tools and equipment that created low noise, low vibration and produced minimal debris. Any use of highpercussion tools would have compromised the structural integrity of the surrounding structure and caused high levels of noise. Working indoors in a relatively confined space, the team from Chicago Cut had to use electrical equipment that produced no emissions and wear the necessary items of personal protective equipment.

Chicago Cut was given two eight-hour shifts to complete the trench work, so the company’s GPR technician, Samantha Hopkins, visited the site one day prior to the start of cutting. The technician utilized a PS 1000 unit from Hilti to scan the required floor areas and produce imaging data. Approximately 400 square feet was covered in four hours, during which time the technician was able to map out the location and depth of all objects found for the saw operator to avoid.

The GPR equipment was able to help the technician identify different types of material within the concrete and any voids present within or below the slab, which was also useful information for the other contractors and the property owners. GPR findings identified targets in the trench that H&R Johnson Bros. wanted to use for the new furniture installation. After the findings were reviewed by all parties, adjustments were made to the installation plan.

The finished trench, showing exposed piping and other objects within the concrete floor.

The finished trench, showing exposed piping and other objects within the concrete floor.

Once the trench location was finalized, concrete cutting work began. Operators Matt Bartels and JR. Woodruff used a 10-horsepower CC1300 electric flat saw from Diamond Products fitted with an 18-inchdiameter blade to make the 2.13-inch-deep cuts for the trench. A K3000 hand saw from Husqvarna was also used for some areas that required cuts. Water control was the cutting contractor’s number one challenge during this stage of the job, based on the office below being occupied. A wet vacuum was employed to collect water and slurry during the work.

All 2,000 linear feet of concrete sawing was completed in eight hours. With all flat sawing and hand sawing work done, a Chicago Cut operator then began to chip out all concrete within the cut lines of the trench using a Bosch hammer drill. The operator was careful not to exceed the specified depth of the trench or hit any of the objects detected by the GPR equipment. The entire trench was chipped out in eight hours.

“There was some concern because of the voids present in the clay tiles. We had to be extremely cautious chipping out the areas because if we went past our mark, the water would travel into any cracks created and through the voids in the tile to the ceiling of the office below,” said Bob Hopkins, Vice-President of Chicago Cut. “We had two eight-hour shifts to complete all tasks and the job was finished on time.”

The professionalism of the cutting contractor did not go unnoticed by the property owners either. Bart Crosby of Crosby Associates expressed his satisfaction with the work, saying, “The Chicago Cut team did a fine job and created no disturbances. The positioning of the trench was critical, as it determined where our new furniture could be placed and we did not want any exposed cabling. It turned out great.”

A sweep of the building—in this case a scan—enabled this CSDA member to complete a delicate concrete cutting job in the Chicago Board of Trade Building successfully. The growing use of GPR imaging is helping to reduce accidents on sawing and drilling jobsites as hidden objects and hazards are being identified and avoided. Combining this equipment with diamond tools is proving to be a winning combination.

The Chicago Board of Trade was established in 1848 and is one of the world’s oldest futures and options exchanges. More than 50 different options and futures contracts are traded by over 3,600 members through open outcry and electronic trading. Volumes at the exchange in 2003 were a record breaking 454 million contracts. The Chicago Board of Trade took shape to provide a centralized location, where buyers and sellers can meet to negotiate and formalize forward contracts. The Board of Trade moved to its current location in 1885, but the original building was rendered structurally unsound during the 1920s and was subsequently demolished in 1929. Upon learning of the condition of the building, architectural firm Holabird & Root was given the task of designing a new building and construction began almost immediately after the demolition of the old one. The new Chicago Board of Trade Building opened the following year, in 1930. At 605 feet tall, it was the tallest building in Chicago until the Richard J. Daley Center superseded it in 1965. In 1977, the Chicago Board of Trade Building was designated a Chicago Landmark and is now classed as a National Historic Landmark.

Company Profile
Chicago Cut Concrete Cutting, Inc. has been in business since 2012 and joined CSDA the same year. The company is based in Schaumburg, Illinois and services the entire Chicagoland area. Chicago Cut Concrete Cutting, Inc. is a woman-owned business, has 20 operators, 20 trucks and offers the concrete cutting services of flat sawing, core drilling, wall sawing, GPR imaging and hot tar sealing. The company employs CSDA Certified Operators.

Resources
General Contractor:
Brennan Electrical, Inc.
Sawing and Drilling Contractor:
Chicago Cut Concrete Cutting, Inc.
Schaumburg, Illinois
Phone: 773-282-2288
Email: hops@chicagocutcc.com
Website: www.chicagocutcc.com
Methods Used: GPR Imaging, Flat Sawing, Hand Sawing

Author: Russell Hitchen

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