Meter cuts the costs of testing new concrete
The following is a document reprint by Tom Greenwood, The Detroit News (Thursday, July 17, 2003)
One would be hard pressed to say that concrete and wine have something in common, but they do: They're both at their best when they've matured.
With wine you check the label, but it's more complicated with concrete. Up until now, road engineers have had to take samples from the fresh concrete and subject it to high pressure testing to determine its hardness.
Only in this way can engineers determine the earliest point at which motorists can begin to drive on the new surface. The sampling is accurate, but time consuming and expensive. It may also be on its way out.
The Michigan Department of Transportation is now testing a high-tech, noninvasive procedure to determine the cure rate of concrete that appears to be accurate, instantaneous and inexpensive.
"They're called maturity meters," said Tim Stallard, a concrete engineer with MDOT's materials research and testing group.
"Basically it's an electronic measuring device that is buried in the concrete. The meter collects information about the concrete as it cures (hardens) and can be checked electronically with a small, hand held device that's similar to a Palm Pilot."
Currently MDOT is testing the maturity meters on Grand River, where the road is being completely reconstructed between Beck and Novi Roads, in Novi, by Tony Angelo Construction. "Maturity meters have been around since the 1940s," Stallard said.
"But all the other meters used wires to relay information. On a busy construction site sometimes the wires were cut or torn out. It's a complicated procedure."
The newer meter is a dark gray rectangle about six inches long with a bar code on one side and a light emitting diode on the other. Its software program has been designed by Wake, Inc., in Sturgis, and is powered by a 3.5 volt battery.
Here's now it works: The meter is attached to a section of rebar and is submerged in the concrete about a foot from the curb. Its exact location is stenciled into the concrete so engineers can find it without any problems.
"The meter collects information and stores it until I contact it with this," Stallard said, holding up a small computer.
"The meter catalogs a great deal of information, including the current temperature of the concrete; the temperature when the concrete was poured; the date it was poured and the dates of when it was previously checked."
Engineers use the internal temperatures to chart the growing hardness of the concrete. "It tells us when the concrete has matured enough so that motorists can begin to use it," Stallard said. "That's especially important to business owners who want customers to have access to their shops as soon as possible."
Because this is an experiment, MDOT is also testing the concrete in the old manner, in which four cylinders of concrete are drilled out of the road surface and then tested. The cylinders are then pressure tested for hardness. So far, the readings from the cylinders and the maturity meters have been almost identical.
Currently the meters cost about $50 each, but the price will drop if MDOT decides to purchase the meters in bulk. Stallard estimates MDOT will use 40 to 50 of the meters on the Grand River project. The meters can also be used in bridge abutments and decks, driveways, tunnels and under water.
Now, don't you wish your kids came with maturity meters?
Commuter columnist Tom Greenwood can be contacted at commuter@detnews.com; at (313) 222-2023 or by writing to The Detroit News, 615 W. Lafayette, Detroit, MI 48226.
One would be hard pressed to say that concrete and wine have something in common, but they do: They're both at their best when they've matured.
With wine you check the label, but it's more complicated with concrete. Up until now, road engineers have had to take samples from the fresh concrete and subject it to high pressure testing to determine its hardness.
Only in this way can engineers determine the earliest point at which motorists can begin to drive on the new surface. The sampling is accurate, but time consuming and expensive. It may also be on its way out.
The Michigan Department of Transportation is now testing a high-tech, noninvasive procedure to determine the cure rate of concrete that appears to be accurate, instantaneous and inexpensive.
"They're called maturity meters," said Tim Stallard, a concrete engineer with MDOT's materials research and testing group.
"Basically it's an electronic measuring device that is buried in the concrete. The meter collects information about the concrete as it cures (hardens) and can be checked electronically with a small, hand held device that's similar to a Palm Pilot."
Currently MDOT is testing the maturity meters on Grand River, where the road is being completely reconstructed between Beck and Novi Roads, in Novi, by Tony Angelo Construction. "Maturity meters have been around since the 1940s," Stallard said.
"But all the other meters used wires to relay information. On a busy construction site sometimes the wires were cut or torn out. It's a complicated procedure."
The newer meter is a dark gray rectangle about six inches long with a bar code on one side and a light emitting diode on the other. Its software program has been designed by Wake, Inc., in Sturgis, and is powered by a 3.5 volt battery.
Here's now it works: The meter is attached to a section of rebar and is submerged in the concrete about a foot from the curb. Its exact location is stenciled into the concrete so engineers can find it without any problems.
"The meter collects information and stores it until I contact it with this," Stallard said, holding up a small computer.
"The meter catalogs a great deal of information, including the current temperature of the concrete; the temperature when the concrete was poured; the date it was poured and the dates of when it was previously checked."
Engineers use the internal temperatures to chart the growing hardness of the concrete. "It tells us when the concrete has matured enough so that motorists can begin to use it," Stallard said. "That's especially important to business owners who want customers to have access to their shops as soon as possible."
Because this is an experiment, MDOT is also testing the concrete in the old manner, in which four cylinders of concrete are drilled out of the road surface and then tested. The cylinders are then pressure tested for hardness. So far, the readings from the cylinders and the maturity meters have been almost identical.
Currently the meters cost about $50 each, but the price will drop if MDOT decides to purchase the meters in bulk. Stallard estimates MDOT will use 40 to 50 of the meters on the Grand River project. The meters can also be used in bridge abutments and decks, driveways, tunnels and under water.
Now, don't you wish your kids came with maturity meters?
Commuter columnist Tom Greenwood can be contacted at commuter@detnews.com; at (313) 222-2023 or by writing to The Detroit News, 615 W. Lafayette, Detroit, MI 48226.
