Machine Design

Cement done yet? New sensor will say so

An Elizabethtown College professor has developed an embedded sensor that functions in cement much like a thermometer in a Thanksgiving turkey.

Just as a meat thermometer shows when your turkey is cooked, a sensor in concrete can monitor how quickly water involved in the curing process chemically combines with Portland cement. Nathaniel Hager III, an adjunct faculty member in Elizabethtown's physics and engineering department, is conducting the research. The college is in central Pennsylvania.

Hager embeds a disposable sensor in a concrete structure when the cement is poured. He then beams fast electrical pulses at the sensor to produce reflections. Reflected pulses contain distortions generated by both unreacted and reacted water molecules when they combine with Portland cement. Tracking these two signals along with cure time better characterizes the cure process and identifies irregularities that lead to improper cure. Essentially, the technique looks for signals that correspond with cement strength. An absence of such signals indicates something is wrong.

The system, dubbed Time-Domain-Reflectometry (TDR) Concrete Cure Monitoring, is expected to find use testing structures to see if cement is fully hard, or on multilevel structures to determine when to pour a second layer. It also could help identify residual moisture in cement floors, says Hager. This could minimize moisture damage and reduce wait times before surface coatings, like epoxy, are installed.

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