In order to develop a specification for concrete maturity, the Michigan Department of Transportation (MDOT) was looking for a contractor and a suitable project in order to test the use of a possible wireless concrete maturity monitoring system (CMMS).
MDOT in the past couple of years has experimented with the use of a CMMS on a couple of select projects around the state. However, the CMMS was not used as a full-scale testing system on any of their selected projects. By forming a partnership MDOT and Tony Angelo Cement Construction Co., Novi, Mich., began a study in May 2003 to test the use of a CMMS on a project in Michigan.
The objectives of the study were to use a wireless CMMS on a project in Michigan from beginning to end to monitor the strength gain in an effort to minimize traffic interruption and provide real-time data. Additionally, the study was intended to provide MDOT feedback from the contractor point of view to help in the potential development of a maturity specification.
Grand’s scheme of things
The test site for the wireless concrete maturity system was the Grand River Avenue reconstruction project from Beck Road to Lanny’s Road in Novi. The owner of the project was the Road Commission for Oakland County and the design and inspection was done by JCK and Associates of Novi.
The project involved removing the existing two-lane concrete road, which had been overlaid with asphalt, and replacing it with a five-lane concrete road with separate concrete curb and gutter. The 1.6-mile project was lined with over 40 businesses that were affected by this construction. The complexity of the job was increased by the type of business in this area. For example, a transit mix concrete company, a sand and gravel hauling company and an automotive supplier that runs multiple shifts all reside around the work. This project was constructed concurrently with the reconstruction of the Grand River Bridge over the CSX Railroad which was located at the east end of the project.
The CMMS is a combination of technologies. There are three main components to it: (1) a radio frequency tag (IQ8T) developed and patented by Identec Solutions of British Columbia; (2) software developed by International Road Dynamics (IRD) of Saskatchewan; and (3) a portable hand-held device that contains a PCMCIA card.
The IQ8T tag that is embedded into the concrete is 5 1/8 in. long, 1 1/16 in. wide and 7/8 in. tall and weighs only 1.75 ounces. The tag has a five-year battery life and can be read through 8 in. of concrete. The IQ8T tag, which contains a thermometer, 8-Kb memory storage, battery and remote transmitter, is able to talk with the PCMCIA card through radio frequency identification. The portable hand-held device with an expansion pack and PCMCIA card operates the pocket concrete software program. It is able to export to CSV files the tag ID, location of the tag, logging interval, pour time and date, sample count, average temperature, high and low temperature, time temperature factor (TTF) and strength.
Prior to the paving on the Grand River Avenue project, a 9-cu-yd test batch was made at a separate location with the same materials that were intended to be used on the Grand River project. The mix design for the test batch was a 5.6-sack mix with 35% ground granulated blast furnace slag cement (GGBFS) and 6AA blast furnace slag for coarse aggregate.
From the test batch, 20 cylinders were molded and one IQ8T tag was placed into one of the cylinders. The cylinders were then field cured and broken at 1, 2, 3, 5, 7 and 28 days. Prior to all compressive strength cylinder breaks a reading was made from the cylinder with the IQ8T tag in it. This reading would provide the TTF. By having the TTF and the compressive strength results a maturity curve of strength vs. TTF is created. This information, which is specific to the test batch and materials used to make it, are then entered into the hand-held device. This maturity curve, along with IQ8T tag readings from tags placed in the new roadway, predict the strength of the concrete.
Tagged for success
On the Grand River Avenue reconstruction project, 19 IQ8T tags were placed into the concrete. The IQ8T tags were placed onto No. 5 epoxy-coated rebar with electrical zip strips. The tie bars with the IQ8T were then placed into the aggregate base with tie bar spades. A total of two to three tags were placed per day.
The CMMS was an important tool used in the reconstruction of Grand River Avenue. The maturity system provided instant real-time concrete strength results. Without attaching a box to any wires coming out from the concrete slab, Tony Angelo Cement Construction Co. could monitor the strength gain of the concrete through a wireless transmission as often as they would like to. During critical times readings were often taken a couple of hours apart to monitor the strength in an effort to move traffic onto the concrete at some of the businesses.
The maturity systems on this project helped to eliminate the dependence on the person performing the concrete series testing. All too often the concrete results on some projects can’t be obtained because the cylinders are still in the field, the testing person cannot be found, the cylinders are in the lab but have not been broken or the cylinders were destroyed in the field and they are no longer any good. By using the CMMS the results were right there in the hand-held device.
The CMMS also helped the project from the standpoint of scheduling. Operations that needed to be conducted following concrete paving and curing could be scheduled with confidence from the maturity readings. For example, pouring of driveways, curb-and-gutter and joint sealing could all be scheduled as early as possible by knowing how the concrete is gaining strength.
The disruption to local businesses was reduced by using the CMMS. By knowing the concrete strength with the click of a button, traffic at businesses which were going through gaps in the mainline concrete pavement could be switched on the pavement and the gaps filled as soon as the proper strength was obtained.
The CMMS provided good concrete strength-gain results for the Grand River Avenue reconstruction project. The results were found to be within 4-11% of the concrete cylinders that were made for the project for prior to 28 days. The CMMS was easy to use, performed terrific and became a valuable tool to the reconstruction of Grand River Avenue. All of the tags placed on this project worked. This project helped provide feedback to MDOT, which in turn developed a special provision for the use of concrete maturity testing titled Maturity Method for Determining Opening to Traffic Time.