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High Concrete is working with Elizabethtown College and professor Nat Hagar to validate the time domain reflectometry system for mix designs used in a High Concrete plant.

The work was patented in 2004 and published as a full-length article in the Journal of Applied Physics in November 2004. An initial field-portable instrument was demonstrated in 2005 through our relationship with Hyperlabs Inc., a manufacturer of ultrafast TDR instruments. A small amount of funding was obtained in 2006 to begin a rigorous comparison between unreacted water signals and compressive strength, as well as other measures of cement hydration.

The lab is located at Elizabethtown College, Elizabethtown, Pa. Nat Hagar has been adjunct professor at Elizabethtown since 1994, teaching introductory physics and providing senior projects in the lab for students. Hager provides the electrical-measurement expertise for projects while Roman Domszy provides the chemical and material science expertise.

Both men have collaborated for more than 20 years since working at research and development at Armstrong World Industries in the 1980s.

Future direction

With the basic signals identified, a practical prototype instrument demonstrated, and a patent in place, there is a critical need to rigorously compare signal evolution with relevant concrete properties to determine if the system can be used as a predictor of properties.

Since a prediction of compressive strength is desirable, the emphasis should be on demonstrating rigorous correlations between free-water signal and compressive strength, as well as accepted measures of cement hydration. In the process, we also quantify relations between free-water signals and initial water content, in addition to residual content at longer stages of cure.

High Concrete Innovations is working with Elizabethtown and Hagar to validate the system for mix designs used in a precast plant. A sample was brought from a High Concrete plant to the laboratory at the college and embedded with a TDR sensor and thermocouple probe. The entire TDR spectrum is recorded as a function of cure time, along with the sample temperature, noting correlations between free-water concentration and reaction exotherm during the cure.

Simultaneously, samples are taken from the mix and analyzed by Differential Scanning Calorimetry (DSC) for calcium hydroxide concentration, a byproduct of the hydration reaction. Initial tests show clear agreement between free-water concentration, reaction exotherm, and calcium hydroxide concentration under differing cure conditions. Shortly, we plan to begin similar tests in the laboratory using field portable pulsing units, which could then be transferred to the production facility in Lebanon for actual plant tests.

The testing with High Concrete and Elizabethtown College is part of a program to develop a concrete hydration monitor which includes SBIR, the National Science Foundation, PennDOT, the Federal Highway Administration, and other agencies. For further information on the testing, visit www.msi-sensing.com.

— Author Paul Ramsburg is the regional quality director at High Concrete Group, Denver, Pa., and writes regularly for THE CONCRETE PRODUCER. You can contact him atPRamsburg@high.net. Nat Hagar, adjunct professor at Elizabethtown College, assisted in writing this story.