Determining the hardness of newly laid concrete is, well, hard. A variety of factors, including humidity and temperature, can affect the curing process. Today, construction crews test sample concrete cylinders by crushing them, but that doesn’t always prove accurate; the cylinders could be stored under different conditions, and the sheer mass of a slab of concrete can affect how it cures.
The Michigan Department of Transportation has solved the problem using RFID. Three years ago, it started working with Identec Solutions, a Canadian provider of active RFID tags with temperature loggers. MDOT embeds Identec active tags, which operate at 950 MHz, in concrete to get accurate temperature readings for the concrete.
The MDOT also worked with another Canadian company, International Road Dynamics (IRD), which developed algorithms that calculate the hardness of fresh concrete based on its temperature. Identec’s tags and the IRD software are sold as a package by a Michigan company called Wake, which offers a PCMCIA reader that turns an HP iPAQ or other PDA into a handheld hardness detector.
The active tags can cost from $40 to $70, according to Warren Atkins, Wake’s president. But road crews need to place only four or five tags in a stretch of concrete laid in one day to get an accurate reading of its maturity. Atkins says the system can save construction crews one day of time per week because once they determine the concrete has reached the proper hardness, the next step in the construction or repair process can begin. Crews complete their work quicker, commuters get back on the road sooner, and the MDOT winds up with hard savings.