New Standard Measure for Structural Integrity Created by Innovative Engineering
Heat, concrete, and civil engineering – hardly strangers, but not exactly the best of friends. ASCE’s 2015 Charles J. Pankow Award for Innovation winner, the Thermal Integrity Profiler, brought the three together to solve a longstanding construction dilemma.
TIP is an innovative testing device based on a pioneering technology that measures the naturally occurring and considerable heat generated by curing concrete (hydration energy) to assess the quality of drilled shafts, bored, augured cast-in-place, continuous flight auger, or drilled displacement piles.
“Throughout the 1970s and 1980s, new bridge construction projects did not have strong quality-measuring systems in place,” said Austin Gray Mullins, Ph.D., P.E., M.ASCE, professor at the University of South Florida and co-inventor of TIP. “Until recently, there were no quality assurance test methods other than a weighted tape to check the depth of the hole and then the rising concrete level. At that time, the as-placed concrete and even the drilling slurry wasn’t reliably checked.”
The concept for TIP originated with Stanley C. Kranc, Ph.D., P.E., M.ASCE, professor emeritus at the University of South Florida. His concept captures temperature readings in the surrounding soil of the cast-in-place concrete of a foundation. Kranc suggested that a cone penetrometer be inserted into the soil around the shaft to measure the temperature, the logic being that if the sensor gets hot, the concrete must be there.
“We had a clear understanding that when concrete cures, it gets extremely hot. And that is good for temperature-based integrity evaluations,” said Mullins. “The curing concrete creates a heat signature that is quite distinguishable – similar to a fingerprint. However, concrete that is cooled does not have a usable heat signature.”
Kranc and Mullins tested their theory and further developed the concept for TIP’s temperature sensor system, which relies on sensors that are inserted into small tubes in the curing shafts, before the concrete has cooled and the material has become impenetrable.
Curing concrete releases a massive amount of energy. A drilled foundation shaft 6 feet in diameter and 80 feet deep, for example, releases more energy than 2 bolts of lightning.
- 1 drilled shaft, 6 ft. diameter x 80 ft. deep 12,800 megajoules
- 2 bolts of lightning 10,000 megajoules
- 2 cross-country trips in a Hummer 11,500 megajoules
- 30 Mark 82 aerial bombs 13,200 megajoules
- 5 months average household usage 13,400 megajoules
Credit: Kevin R. Johnson, MCE, E.I., Ph.D. Candidate, University of South Florida
Pile Dynamics, Inc., of Cleveland, which calls itself the world’s largest manufacturer of foundation dynamic testing, was chosen as the firm to bring TIP to life.
“Using the naturally occurring hydration energy to measure structural integrity was a great concept.” said George Piscsalko, president of Pile Dynamics, Inc. “Gray and Stan’s idea became a reality when PDI designed a commercially viable system to measure this elevated temperature.” The system developed by PDI either casts temperature sensors into the curing piles or passes a thermal probe through access ducts built into the pile.
Pile Dynamics produces TIP’s probe-based and embedded thermal sensor wires. The sensor wires are encapsulated at regular intervals along the length of copper cables. The cables are installed in cast-in-place foundations prior to concrete being poured. As soon as the concrete pour is complete, the sensors start measuring temperatures. Typically within 8 to 24 hours afterward, there is sufficient data for an engineer to approve the shaft’s integrity, allowing construction to continue. This integrity-test timeframe is much shorter than the typical 3 to 7 day waiting period required for previously used concrete integrity tests.
TIP technology is used to evaluate the integrity of cast-in-place concrete foundations such as drilled shafts, bored piles, micropiles, augured cast-in-place, continuous flight auger piles, and drilled displacement piles, and it can also evaluate the shape of slurry walls, for example.
“TIP’s development process took about a year, and then we had our first commercial TIP – after testing and after we built a successful prototype – that was ready for the commercial market,” said Piscsalko.
Piscsalko explained that the TIP system data loggers are connected to the wires as soon as the structure is cast. The data loggers automatically collect temperature data every 15 minutes.
“Piles often have so many variances in structure that affect temperature that are not visible to the naked eye – and we are improving and will continue to improve the product and the software,” said Piscsalko.
Piscsalko said TIP technology is now being used worldwide. TIP’s computerized results can reveal any necks or inclusions in the foundation as it recognizes areas that are colder than average. It also senses bulges by recognizing temperatures that are warmer than average, as well as concrete cover variations, shape of the shaft and cage alignment.
The TIP system was used during the construction of the new Cleveland Inner Belt Bridge. Specifically, TIP sensors were placed inside 16 drilled shafts, each 150 feet deep, which now support the Eastbound George V. Voinovich Bridge in the downtown area of the city.
Mullins believes that the speed at which the TIP was engineered and then built and put into use was simply incredible. “There are many great civil engineering ideas that do not see the light of day; the road is usually long in getting an idea to a finished product. And there are many ideas that never even see the light of day.” Measuring heat just got a whole lot cooler.
Read more about the Pankow Award-winning Thermal Integrity Profiler and ASCE’s 2015 OPAL Awards gala.