Laying down high-tech pavement: Intelligent Compaction takes guesswork out of density


Modern technology is taking the guesswork out of paving the nation’s roads and runways.

“Intelligent Compaction” refers to compaction of road materials such as asphalt, soils or aggregate bases using modern vibratory rollers equipped with an integration of high-precision positioning systems, accelerometers and onboard computer systems. The transmitted information provides feedback to the roller operator regarding the compaction process, said Richard S. Giessel, P.E., statewide quality assurance engineer for the Alaska Department of Transportation and Public Facilities.

Maintaining uniform compaction is extremely important to achieve consolidation and uniformity of materials, thus avoiding pavement failure.

“Traditionally the roller operator must always know what he or she has already rolled,” said Amanda Gilliland, quality control manager for Knik Construction Co. Inc. “Even the best operator can mess this up every once in a while. When you pave for 10-plus hours, rolling can be a bit redundant.”

The on-board computer screen changes color each time the roller passes the same spot, Gilliland said, allowing the operator to keep track of roller passes.

“They just focus on making everything the same color, and they aren’t having to remember, ‘Was this the third or fourth pass?’” she added.

It also helps keep the roller operator honest.

“It is pretty typical to feel pressure to keep up with the paving train,” Gilliland said. “If a roller falls behind they might be tempted to drop a pass and catch up. With this system they have to get everything ‘colored in,’ so it really helps set and maintain the paving speed as well. You can also look at temperatures, speed and impact settings. So if you are having any problems getting density, it is a great tool to use to see why density was not met.”

Data is typically downloaded at the end of a shift for evaluation by contractors and engineers.

 

It isn’t all about the roller

Additional instruments provide even more data input.

A Paver-Mounted Thermal Profiler system mounted on the mast of a paving machine tells the operator the temperature of the hot-mix asphalt mat as it emerges from the paving machine and before rollers begin compaction, Giessel explained.

Pavement temperature plays a key role in pothole prevention, Giessel added. Thermal images generated by a PMTP showing a green area indicate cooler temps and potentially a future pothole.

With a PaveScan Rolling Density Meter — as a standalone or mounted on a truck — a single operator can map the compaction of every square foot of paving laid during a typical shift in about three hours,” Giessel said. “That’s less time it takes a two-person crew to drill density test cores and patch the holes in the new paving.”

However, use of IC does not replace the traditional method of drilling core samples.

Taking a core is physically cutting a sample of the asphalt and measuring its density, Gilliland said. Density specifications and definitions of “good density” vary by state, but in Alaska good density is considered to be 95-percent of Maximum Specific Gravity, she added.

Knik Construction uses other density gauges and cores samples to test for density, Gilliland said. “IC is not yet a substitute for these, in my opinion, but the technology is getting closer to eliminating the need to take cores from the new asphalt.”

 

Sitka airport runway overlay project

Giessel said he first learned of IC in 2012, but it was Gilliland and Bruce Brunette, DOT&PF’s Southeast Regional Materials Engineer, who first brought IC to Alaska.

It was first used by Knik Construction in the 2013 Sitka Rocky Gutierrez Airport runway overlay project in Southeast Alaska.

According to the Federal Highway Administration’s Application Notes on the project, Wirtgen/HAMM Tandem IC Rollers were used with Wirtgen representatives on site to assist with training.

In the end, according to the report, both the mat and joint densities on the runway repaving met full bonus requirements and remained consistent throughout the project.

Since then, Knik Construction has implemented IC in airport runway projects in Ketchikan, Petersburg and Yakutat and IC will be included in the Kalifornsky Beach Road project this summer in Soldotna.

 

Pavement life

Giessel said asphalt pavements can last from six to 30 years, depending on traffic and environmental factors. However, wear on Alaska’s pavement is worse due to high-speed studded tire traffic combined with high daily traffic counts. Giessel cited the Glenn Highway from Airport Heights to the Parks Highway interchange as an example.

“In addition to the insidious damage from studded tires, early pavement failures are caused by low compaction and insufficient bond between paving layers,” he added.

Modifications in material and IC technology were used in last year’s repaving of the Glenn Highway, he said. Engineers hope to get 10 to 15 years of wear versus the six- to seven-year life of past pavements.

Giessel said the DOT&PF recognizes the benefits of IC and currently requires it on major runway and road paving projects.

Most contractors in Alaska have IC-equipped rollers. Upfront cost of purchase or rental is minimal when one thinks of the benefits, Gilliland said.

“Advancing this technology is very important for Alaskans to get better roads that will last longer with less maintenance cost,” Giessel said.

 

Nancy Erickson is a freelance writer living in Moose Pass.