News Release, Kansas Geological Survey, Aug. 13, 1999
Geologists from the University of Kansas, working with the Kansas Department of Transportation, have developed new methods of identifying the types of limestone that produce high-quality concrete. Their suggestions could result in Kansas roads that last longer and need fewer repairs.
With a grant from the Department of Transportation (KDOT), geologists Robert Goldstein and graduate student Jason McKirahan from the KU Geology Department and Evan Franseen from the Kansas Geological Survey studied limestones that are commonly quarried in eastern Kansas. In particular, they focused on a rock layer called the Farley Limestone, deposited here by shallow seas about 330 million years ago.
Today the Farley is quarried in several locations in northeastern Kansas, particularly in the area around Kansas City. Once it is quarried, the limestone is ground up and added to other materials to make concrete.
The geologists studied samples of the Farley from 17 locations in Johnson, Wyandotte, and Leavenworth counties, including quarries, outcrops, and cores recovered from drilling. Analyses show that limestone that has clay dispersed throughout the rock will eventually result in less-durable concrete. The type and amount of clay minerals also affect the quality of concrete.
"Certain clay minerals will absorb water," said Goldstein. "That makes the concrete expand and produces poorer quality concrete.
"That's why limestone that contains no clay, or small amounts of non-expandable clay, produces concrete that is more durable.
The key, then, is predicting where the Farley and other similar limestones contain no or relatively small amounts of clay. Limestones deposited under certain conditions contain much less clay and result in better concrete. The trick is finding those locations.
"Once quarrying has begun in a location, it's important to identify and stay away from those areas where the limestone is of poor quality," said Franseen. "We've suggested several quick and inexpensive methods that quarry operators and KDOT can use to help them do that."
"For example", said Goldstein, "we have recommended the use of a particular tool, spectral gamma-ray logging, that measures the natural radiation in the rock. Because clay-rich zones produce more natural radiation, these measurements can be made to help identify the limestones that are higher in clay."
"By incorporating basic geologic techniques and using gamma-ray logging, staff at quarries and at KDOT can identify differences in the rock layers that affect the quality of concrete," said Franseen. "That should eventually lead to longer-lasting roads."