Feb. 8, 2001 University Park, PA --- Penn State engineers have developed a "smart" maturity meter to estimate and to signal by phone when newly poured concrete bridge supports, pavements, and highway surfaces have reached the correct hardness and strength to be opened to traffic or the next phase of construction. "This method of estimating the strength of concrete can save taxpayer money in reduced cost of quality control and assurance testing," says Dr. Paul Tikalsky, associate professor of civil and environmental engineering and a developer of the prototype.
"In addition, the meter provides information on the status of the actual structure rather than on representative concrete samples, the method most often used today to estimate concrete strength," he notes.
The meter prototype and accessory technology were developed by Tikalsky and David G. Tepke, a doctoral student, as part of Tepke's master's degree research. Tepke completed his master's degree program in December 2000 and is now a doctoral candidate at the University. The new maturity meter is the result of integrating new digital phone technology with an existing concrete monitoring concept. The concept, Tikalsky says, has been around since the 1940s but has only recently been employed in meters on the commercial market. The Penn State prototype is a "next generation" meter that the developers estimate will cost less than those currently available. In addition, the Penn State meter provides real time evaluation and quality control information with cellular technology.
Ambient temperature, the heat generated by the chemical reactions in the curing process itself and the variability in the concrete mixture, as well as other factors, influence the rate at which concrete structures achieve their intended strength. Currently, when concrete is poured to create a structure, small sample castings are made, for test purposes, to represent how the concrete is gaining strength in the actual structure.
The Penn State prototype uses the fact that the internal temperature of the concrete can be directly related to the time it takes to mature. Only a minimal number of castings need to be made for the Penn State method to be effective. To determine the internal temperature, the prototype uses simple thermocouple technology, the same technology used in a digital thermometer, and then integrates it with a computer program-net-on-a-microchip, along with cell phone technology, to provide a "smart" monitoring component.
In the Penn State prototype, sensor wires are snaked through the concrete forms before the cement is poured. After the cement is in place, the wires are connected to the maturity meter which is, in turn, connected to a digital cell phone. By calling up the phone, the developers can download the digital data and use software they have developed to convert the temperature data into a maturity rating.
Tikalsky notes that the system can be used to monitor the status of a structure remotely and sound an alert on a pager or phone when the concrete reaches readiness or an alarm if the concrete is in danger of freezing which can cause serious damage to the maturing structure. The Penn State meter is expected to cost about $2,000 when it is commercially available and to reduce substantially the test castings that need to be made. Since an average of 200 castings are required for each concrete bridge upright, for example, the potential savings represents a significant part of the quality control and assurance testing budget.
Tikalsky also says that the meter has the potential to reduce litigation in connection with assurance testing. Since, when the maturity meter is used fewer castings need be made, the liklihood that castings can be removed from the site and tampered with is also reduced. "People can have more confidence in the results with the maturity meter, because the actual structure is being tested not just a separate concrete sample," he adds.
Tepke recently presented a paper, "Concrete Maturity Progress: A Survey of Departments of Transportation," co-authored by Tikalsky, at the Transportation Review Board (TRB) Annual meeting in January 2001.
"The survey, distributed in all 50 states, was conducted to inform transportation officials and contractors of nationwide progress in using maturity technology as a quality control tool for transportation applications," Tepke says. "While the existing maturity method has been advanced to assist states and contractors in placing high quality concrete, the vast majority of states are not yet using it to its full potential. Most departments of transportation do not have a standard protocol to specify the use of the technology and therefore have no direct means of utilizing maturity data."
Tepke and Tikalsky's paper was selected by TRB from more than 100 as one of four papers to be distributed nationally and internationally. TRB selects and distributes these papers to provide state DOT practitioners with information that has potential for immediate application in their daily operations.
The research was supported by a grant from the Pennsylvania Department of Transportation.
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