Tag Archives: Box Test

Tech Overview Covers Concrete Workability and Test Methods

In its ongoing series of “Observations from the FHWA Mobile Concrete Technology Center (MCTC),” the technology overview covers some practical workability tests for concrete used in slip-form paving.  

The information-packed information sheet provides a description of workability, then details the Box test and the VKelly test, both of which provide an enhanced assessment of concrete workability.

The illustrated publication describes features of both tests and says a common feature of both tests is they measure concrete’s response to vibration and better assess the workability of concrete during field placement. Though both tests can be used in the field, the primary use is during mix design/approval for optimizing concrete mixtures, the MCTC says.

The publication continues with a description of slump and explains why, in spite of limitations, slump testing is also important in concrete mixture evaluation.  A brief summary provides the reader with highlights of one of the MCTC’s latest publications. 

 

Open House Spotlights PEM and Related Testing

An open house event yesterday focused on performance engineered mixtures (PEM), as well as PEM testing methods.  Cosponsored by the Federal Highway Administration, Illinois DOT and Illinois Chapter-ACPA, the event began with presentations describing the PEM approach.  Peter Taylor of the CP Tech Center provided an overview of the PEM approach,  James Krstulovich of the Illinois DOT,  provided an agency perspective on PEM, and Mike Ayers, Illinois Chapter, provided an industry perspective.

The event, which began in Moline, IL, was followed by PEM test demonstrations at Hahn Ready Mix, Sand & Gravel in nearby Davenport, IA.  About 40 professionals representing the FHWA, Illinois DOT, industry and the CP Tech Center attended the open house event. 

PEM was developed in part, due to the traditional testing and acceptance methods, which are based on factors such as strength, slump and air.  Although these are measures of quality, they have little correlation to future performance, says the CP Tech Center, which notes the goal of the PEM transportation pooled fund is “to bring new testing technologies to state agencies and assist in new test methods that will help deliver durable, long-lasting concrete.”

“We need to make a spec that works better than what we have at the moment,”  Taylor said as in his opening remarks.  “As we move away from prescriptive specs, method specs– and move toward giving the contractor and the producer ownership of their mix designs, we have to keep moving away from the prescription, giving the freedom and innovation over to the people making (the concrete),” Krstulovich said.  Ayers said, “What we don’t consider in pavement design is durability issues, and that’s what’s coming back to haunt us.  Performance engineered mixtures is going to go a long way in alleviating that problem.”

Following the insightful presentations, the DOT also provided a brief overview of the I-74 reconstruction project, a joint project among the Illinois and Iowa DOTs to improve the I-74 corridor from Moline to Davenport.  The project includes the replacement of the I-74 bridges over the Mississippi River as well as interchange ramp reconfigurations and local roadway improvements, according to the I-74 River Bridge website.

The open house continued in the afternoon with demonstrations and interactive discussions about our testing methods that support PEM.  They are: the Super Air Meter, which measures air-void characteristics of concrete; surface resistivity testing, a rapid measurement technique to determine the permeability of concrete; the box test, a measure of workability; and the V-Kelly test, also a measurement of workability.

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Photo:  (L-R) Mike Ayers and Peter Taylor discuss surface resistivity testing during the PEM workshop.  (Photo by Bill Davenport for ACPA)

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