On Nov. 24, members of the concrete industry gathered in the civil engineering labs at the Engineering Research Center to test the air content of concrete. The group, which was hosted by the Center for Training Transportation Professionals at the University of Arkansas, consisted of testing operators from four different states, as well as engineering students from the University of Arkansas and Pittsburg State University in Kansas.

The goal was to obtain testing information to assist in developing a precision statement for the Type B air pressure meter, which measures the air content in concrete. Concrete that is exposed to freezing and thawing is designed to contain a certain amount of air to prevent damage to the concrete when it freezes.

All concrete contains excess water and when this excess water freezes, it expands. The air content allows for this expansion to occur without cracking the concrete. On the other hand, too much air in concrete compromises its strength. Therefore, measuring the air is an important test on freshly mixed concrete and the precision statement is an indicator of the variability that can be expected among test results. 

The air content of concrete is determined using a method prescribed by ASTM International, an organization that develops and publishes standards, for evaluating materials such as concrete. However, ASTM C231, “Standard Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method,” does not currently include precision information for the Type B air pressure meter. The precision statement sets a limit on the amount of variation between two results of the same test.

In order to test the precision of the air pressure meter, staff at the CTTP along with the help of APAC Central, mixed concrete with a pre-determined quantity of air. Then, test operators ran tests on the concrete to compare the results. The sixteen participants each ran three tests each at 6 different air levels. The group conducted 288 total tests on the concrete. CTTP staff reported that they successfully obtained all the needed data. They are now analyzing the information so that the precision statement can be written.

“Concrete tests are essential for the construction industry,” explained Lance Heiliger. Heiliger is in charge of quality control at GCC Mid-Continent Concrete Co. in Northwest Arkansas, and he participated in the testing. “This is one of those test results that is often debated and it really needs to be standardized.” 

This testing event was a joint effort, organized by Frances Griffith, administrator of the Center for Training Transportation Professionals in the department of civil engineering, and by Joe Hug, technical services manager for Monarch Cement Co.  

The testing would not be possible without the help and support of several members of the concrete industry. APAC Central supplied the use of one of their trucks to mix the concrete. Other organizations that supported the center’s efforts include Arkansas Ready Mixed Concrete Association, Ash Grove Cement Company, BASF, Greenhill Concrete, GCC, Materials Testing of Arkansas, Monarch Cement, Murray Decorative Supply, Pittsburg State University, Razorback Concrete and Springfield Ready Mix.

Cameron Murray, a University of Arkansas student working on a master’s degree in civil engineering, explained that participating in the testing was a valuable experience. “It's good practice on the test methods that we will potentially have to use or evaluate the results on a regular basis,” he said. “It's also good to see what goes on behind the scenes of these specifications, how they get the numbers that go in the specifications. That's something not many students get to see.”

Griffith explained that student involvement in projects like this benefits both the students and the university. “We are very happy to have students, who understand the importance of these tests, participate in projects that help shape industry standards,” she said.