CONCRETE SOLUTIONS

Article December 28, 2000
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A new concrete pavement can be opened to traffic when it has achieved adequate strength

A new concrete pavement can be opened to traffic when it has achieved adequate strength. How that strength is measured and knowing when the required strength is reached often takes on new importance. Opening without unnecessary delay can result in substantial savings of money and time, and an increase in safety due to shorter exposure of the work-zone area.


Maturity testing provides a reliable technique for continuous monitoring of concrete strength gain. This enables any pavement to be opened to traffic without delay, whether or not it is a fast-track project.


The maturity concept, as described in ASTM C1074 and C918, is based on the principle that strength gain is a function of time and temperature, and correlation to strength can be established. The maturity value is the sum of the degree-hours from initial concrete placement to a given time during the curing process.


The Iowa Department of Transportation has been using the method for several years and found it to give consistent and acceptable results.


Test beams or cylinders do not necessarily measure the actual concrete pavement strength. The beam or cylinder is not the same as the concrete in the pavement. It does not have the mass of the pavement, the same moisture conditions or the same temperature during the curing process. It can be tested and a strength determined, but that is only the strength of the specimen, not the strength of the in-situ pavement. There is no easy way to know how large the difference may be.


The maturity method is a two-step process. Initially, a relationship is established between the maturity values and the concrete strength as measured by tests of beams or cylinders. The development of the maturity-strength curve is done at the beginning of construction using project materials and mixing equipment. The second step is the instrumentation of the concrete to be measured. Temperature probes are installed in the concrete and the temperature is measured periodically. From these measurements, along with the age at which the measurements were taken, maturity values are determined by a maturity meter or temperature measuring device and a computer or calculator.


Iowa has concluded that maturity testing reduces construction time and traffic delays, and improves public relations during construction.


About the author: 
Packard is director of engineering-design for the American Concrete Pavement Association. You may write him in care of the editor.
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