Research leads to improving airport runways

Look out just about any aeroplane window during takeoff or landing, and chances are you will see a jigsaw puzzle pattern in the tarmac.

The deterioration in some concrete pavements is an issue that plagues a number of US airports. Experts have speculated that certain de-icing and anti-icing chemicals used on airfield pavements may play a role. When the average two-mile runway costs about $45 million to replace, it is a big problem.

Although his research study officially ends in May 2006, Clemson University civil engineering professor Prasad Rangaraju has the green light from the American Federal Aviation Administration (FAA) to solve an escalating problem. The FAA is implementing Rangaraju's test method now at airports across the country in an attempt to curtail further cracking.

Rangaraju developed a test method that determines whether or not a concrete airfield pavement will hold up under the use of de-icers and anti-icers which keep snow and ice off the ground at airports. The Clemson researcher says not all concrete is susceptible to cracking. In his study he found some mixtures held up much better than others.

"These are basic chemistry issues," Rangaraju said. "If a runway is going to be built, the aggregates in the concrete mixture need to be tested first to see how they react in the presence of these de-icer and anti-icer solutions. Certain aggregates hold up just fine. Depending on the findings, we can also adjust the concrete mixture by using certain supplementary cementing materials and/or chemical admixtures to mitigate the reaction and prevent the distress from occurring. This is important not only for new runways but also for patching cracks and other areas of deterioration in existing airfields."

Field observations of airports in Atlanta, Denver and Colorado Springs suggested de-icers may have played a role in tarmac distress. In lab studies, Rangarajan confirmed that de-icers are capable of triggering this type of problem. Greenville-Spartanburg International Airport in South Carolina was observed to experience no cracking for several years since the concrete was replaced.