MATURITY MATTERS

Determining the strength of concrete is critical when it comes to getting traffic back on the road.

A concrete cylinder is checked for compressive strength.

Concrete pavement starts out looking like a muddy jumble of rocks and dirt. The mix contains water, cement, aggregate, fly ash and additives. When combined, a chemical reaction occurs, and concrete matures as water hydrates the cement. It’s the job of UDOT engineers, contractors, transportation technicians and lab workers to verify when the compressive strength of concrete has been reached so a road can be put in service or the next construction process can be started.

Determining the strength of concrete takes expertise, time and effort. Concrete can be damaged if the wrong assessment is made so before freeway traffic hits new pavement, or back fill is placed against a retaining wall, workers systematically test the concrete to make sure adequate strength is reached.

Traditionally, transportation technicians first take field measurements to check for consistency, air and content of the mix. Then, the concrete is poured into cylinders using the same mix used for the project. Cylinders are tested in pairs at set time intervals using a mechanized press that measures compressive strength.

The traditional testing method is time and labor intensive. Costs for the process can add up, especially if the predetermined testing interval falls on weekends or after normal work hours – technicians need to retrieve and transport the cylinders from the field to the lab and lab workers need to be on hand to run the test.

The UDOT Region One Materials Lab is using technology to predict compressive strength of concrete while saving up to eighty percent of testing costs.

A maturity meter and sensor

The method uses sensors placed in concrete and a maturity meter to measure time and temperature. The data, along with a math formula, can be used to chart a maturity curve specific to a concrete mix. The curve can be created using sample cylinders before the concrete is placed in the field. Or, meter readings can be done concurrent with construction. The maturity curve allows workers to predict when compressive strength is reached.

The cost for testing one batch of concrete multiple times using traditional methods can easily add up to a few hundred dollars. One sensor can be read multiple times and costs less than $50 for the same information.

“A maturity curve shows the progress of the chemical reaction,” says Scott Nussbaum, Region One Materials Engineer. “Using maturity meters helps reduce risk, save money and open to traffic as soon as possible.”

A maturity curve helps predict when compressive strength is reached.

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