President Biden just unveiled a $4 billion blueprint to update a 150-year-old rail tunnel in Maryland as the latest project in the federal government’s bid to overhaul U.S. concrete infrastructure.
The newly named Frederick Douglass Tunnel will replace the Baltimore & Potomac Tunnel (B&P), which dates back to the Civil War era and is the oldest rail tunnel in the United States.
This piece of American rail history is described by Amtrack as suffering “from a variety of age-related issues such as excessive water infiltration, a deteriorating structure, and a sinking floor. There are no fire and life safety systems that help keep passengers safe in the event of emergencies, and excessively costly maintenance is required.”
It’s little wonder why the repair cost is excessive when the structure was completed in 1873 and received temporary fixes from 1910 through the 1980s. However, none of those repairs were meant to be permanent, and now, crumbling brick, exposed rebar and conduit, and falling concrete are just some of the problems causing delays for 99% of the trains running through the B&P corridor.
The Bipartisan Infrastructure Law, also known as The Infrastructure Investment & Jobs Act, which will pay for the tunnel replacement, was met with great anticipation by construction professionals of all kinds. Everyone from Civil Engineers to manufacturers and general contractors have been excitedly awaiting the release of funds so that neglected dams, bridges, roads, tunnels, and airport terminals can support the nation’s needs.
Nowhere is that need greater than in concrete infrastructure.
Concrete can also be the most challenging to assess because in most cases, the damage occurs from the inside out. The degradation is sometimes referred to as “concrete cancer” due to its unseen nature because by the time obvious cracks, pitting, and crumbling are evident, the interior structural integrity of the once-robust structure is a mess.
Which means it’s a small miracle that the worst problems with the B&P Tunnel have been delays and not a complete collapse.
That has not been true for several high-profile concrete infrastructure failures. Dozens of other aging concrete structures fail every week. Most of them never make your nightly news.
Here are two examples of the extreme damage that crumbling concrete can cause:
On January 28, 2022, Pittsburgh’s Fern Hollow Bridge collapsed, dumping multiple cars and a city bus into a ravine, injuring eight people, and severing a major gas line that had to be shut down to avoid explosions and further injuries. The bridge itself was steel that was supported by a concrete superstructure and covered in concrete decking, both of which were rated as poor by a 2019 NTSB assessment. The federal government has pledged $1.4 billion to rehabilitate Pennsylvania’s bridges as part of its infrastructure plan.
Another high-profile case is the now-infamous Champlain Tower condominium building in Surfside, Florida. Inspectors who viewed the foundation of the structure after its 2021 collapse that killed 98 people reported naked rebar hanging from the ceiling, rusting from long exposure to the salty, humid sea air which had spent years eating the concrete it was installed to support.
The public outcry was immediate, and led to the unanimous passage of the Surfside Bill, which requires inspection of every high-rise condominium in Florida (some 1.52 million units) by the end of 2024.
So, engineers, architects, and contractors who are planning and executing large-scale municipal infrastructure projects are faced with two overlapping problems:
- How do you gauge the structural integrity of existing concrete structures so they can be maintained and repaired?
- How do you safely build, repair, and maintain concrete structures to avoid failure and collapse?
How to Visualize Concrete Infrastructure Without Cutting or Coring (Non-Destructive Testing)
Let’s tackle the second question first. There are several ways to go about discovering what’s going on inside post-tension concrete. One of those ways, GPR (ground penetrating radar), is what GPRS was built on. GPR, sometimes supplemented with Electromagnetic (EM) locating, allows a technician to scan the existing concrete structure to locate conduit, rebar, water and sewer lines, telecom lines, and voids so that you can avoid utility strikes, cross bores, and other hazards when cutting into existing concrete structures.
Accurate and complete GPR and EM imaging is vital to the success of any concrete infrastructure project because you cannot cut or drill into existing structures without knowing what’s underneath – unless you’re willing to risk tens of thousands of dollars in damage, two to three months of downtime, and serious injury to your crew.
This is why GPRS Project Managers are SIM certified. SIM stands for Subsurface Investigation Methodology. It is the highest standard of training for non-destructive testing (NDT) in the concrete industry and it is the backbone of how we have maintained a 99.8%+ accuracy rate in concrete imaging and utility locating on over 350,000 jobs nationwide.
An elite GPRS Project Manager, armed with a portable GPR device, can so accurately map the features inside a slab that when they mark out a clear zone for cutting or drilling, we guarantee their accuracy.
So, that’s how you can easily see specific PME and telecom features inside your slab. But what about gauging the structural integrity so that you know where maintenance and repair are required?
Non-Destructive Concrete Structural Integrity Testing
The most accurate and complete non-invasive concrete analysis comes from Ultrasonic Pulse Velocity (UPV) and Tomography tests.
These methods can assess cold joints, honeycombing, and more to provide a complete picture of what’s really happening inside your concrete. However, they require specialized and expensive equipment, and highly trained technicians to perform. So, many pieces of concrete structure are going untested due to the sheer volume of concrete requiring analysis vs. the professionals able to do the testing.
Even in Florida, the initial structural analysis guidelines in the new law require only a visual assessment and maybe a sounding test, also known as the 9-iron or hammer test, where a person uses a piece of metal or a rebound hammer to tap the surface and listen/feel for voids in the structure. As you can imagine, there is enormous room for error in those less technical methods.
Your only other option for “seeing” inside a concrete slab is to perform invasive testing or potholing, which causes damage to the structure while testing it for damage. While potholing is sometimes a necessity to verify conditions, it is inefficient, damaging, and counterintuitive when locating PME hazards prior to executing cutting or coring for repairs.
As municipalities across the country begin their infrastructure renewal projects, it is crucial that they utilize the most accurate and advanced subsurface imaging and non-destructive testing methods available to preserve their structures, their budgets, and most importantly, their people. GPRS provides the testing you need to make all of that possible.
What can we help you visualize?