GPRS Project Managers kept a construction project at Massachusetts Institute of Technology (MIT) on time, on budget, and safe by employing precision concrete scanning services to ensure damage-free coring through a concrete slab.
The work occurred within one of the buildings on the 108-year-old, 168-acre campus in Cambridge, Massachusetts. The general contractor on the project intended to core in three locations along the slab and wanted to know where rebar lay hidden within the concrete.
Originally established in Boston in 1861 before the current campus in Cambridge opened in 1916, MIT is one of the preeminent universities in the world. According to the school’s website, it was founded to “accelerate the nation’s industrial revolution.” 101 Nobel laureates, 61 National Medal of Science winners, 33 National Medal of Technology and Innovation winners, and 83 MacArthur Fellows are associated with the university.
A renovation project on such a historic campus naturally garners a lot of attention and scrutiny. The contractor overseeing the work could not afford any delays or disruptions caused by damaging reinforcement embedded within the concrete.
Damage to rebar or post tension cables during coring or cutting concrete can potentially cause immediate structural failure that leads to injury or the death of those on site. And, according to a recent study completed for GPRS by Finch Brands, the average cost to repair damage to rebar or conduit embedded within concrete is $12,000.
To locate and map rebar within a concrete slab, GPRS Project Managers utilize a non-destructive technology known as ground penetrating radar (GPR). A GPR scanner emits radio waves into the concrete, and those waves interact with – or “bounce” off – any subsurface material they encounter. Those interactions are detected by the scanner, and instantly displayed in a readout as a series of hyperbolas that vary in size and shape depending on the type of material that was located.
It takes extensive, specialized training to be able to take a series of hyperbolas and use that to determine the precise location of buried objects. That’s why all GPRS Project Managers (PMs) are certified in Subsurface Investigation Methodology (SIM), the industry-leading training and specification for not only concrete scanning and utility locating but also sewer line inspection and leak detection.
SIM has played a significant role in GPRS achieving and maintaining a 99.8%+ accuracy rate on the over 500,000 utility locating and concrete scanning jobs we’ve completed to date. It was developed to provide subsurface investigators with greater education, advanced field training, and a repeatable process that allows them to accurately locate utilities and other buried objects.
The SIM-certified GPRS Project Managers working at MIT located and mapped the rebar in the proposed coring locations, and then marked their findings – including the estimated depth of the reinforcing material – on the surface of the concrete slab. They were able to complete this work on the same day that the client contacted GPRS, so that the engineers on the project could immediately incorporate this data into their planning process.
Guaranteed Results
GPRS is so confident in the accuracy of our concrete scans that we decided to put our money where our mouth is.
The GPRS Green Box Guarantee is an industry-leading, proprietary program designed to give you peace of mind. It’s simple: when GPRS conducts a concrete scan and places a Green Box within that layout prior to you anchoring or coring that concrete, we guarantee the area will be free of obstructions.
If we’re wrong, we agree to pay the material cost of any damage that occurs.
The Green Box Guarantee helps prevent potentially life-threatening injuries and damages, eliminates project delays, costly repairs and unexpected change orders, and ensures clear communication between you and our field team members about where it’s safe to break ground. It’s just one way we are working to achieve our goal of 100% subsurface damage prevention.
From skyscrapers to sewer lines, GPRS Intelligently Visualizes The Built World® to keep your projects on time, on budget, and safe.
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Frequently Asked Questions
How is ground penetrating radar (GPR) used to identify tendons vs. rebar in a post-tensioned slab?
In post-tensioned structures, we typically find one mat of support rebar near the base of the slab. This mat is generally consistently spaced and remains at a constant elevation. Post-tension cables are generally found above this support mat and “draped” throughout the rest of the structure. The elevation of the cable is usually high near the beams and column lines and drapes lower through the span between beams and column lines. Knowledge of these structural differences allows us to accurately differentiate between components.
Can GPR determine the difference between rebar and electrical conduit?
Yes, in most cases, GPR can accurately differentiate between rebar and electrical conduit. Additionally, GPRS Project Managers will use electromagnetic (EM) locators to determine the location of conduits within concrete. If we can transmit a signal onto the metal conduit, we can locate it with pinpoint accuracy. We can also find the conduit passively if a live electrical current runs through it.
The combined use of GPR and EM locating allows us to provide one of the most comprehensive and accurate professional conduit locating services available.