Dust-Up Over Pavement Preservation

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Changes planned

CRF p-graphStreet application of a preservation substance called CRF has proven results in making streets last longer. It’s worked in Bloomington, where a pilot program is in its third year but where testing began in 2007. This year’s application, however, has resulted in large amounts of dust, causing annoyance to residents and prompting numerous complaints.

Public Works Director Jim Karch has initiated six steps to avoid similar problems in the future.
“We apologize for the inconvenience of the dust this year,” said Karch. “In engineering, creative solutions sometimes cause side effects. We still are sold on the end result – better streets that last longer and may eventually save taxpayers millions of dollars. We have taken steps to mitigate future side effects.”

The City Council and Administration uses pavement preservation as a way to address deteriorating roads and limited budgets

A study in 2011 showed the City needed $60 million to fully repair streets by the conventional process of milling old asphalt and resurfacing. The City amped up its resurfacing program but also introduced preservation methods.

Research on CRF has stretched five decades, and in Bloomington it was first tested in 2007. CRF is what is known as an asphalt rejuvenator. It restores the balance of maltenes and aphaltenes to prevent the street surface from fracturing. It often is applied with a mix that includes 30 percent water.

In Bloomington, however, it is used full strength (100 percent) and has the added benefit of filling cracks in the street. In common language, it has the effect similar to applying a weather sealant to a porch deck.
The City contracts for another road sealant, Reclamite, to protect new and recently resurfaced streets. CRF contains Reclamite but in greater concentration and works to rejuvenate aging streets. That has a major effect on the budget. It costs about $30 per lineal foot to mill down a street and resurface it with asphalt. It costs about $2.50 to use CRF instead.

 

 

 CRF Grundy

Treated vs. Untreated: A photograph from a Grundy County CRF test strip shows a treated portion (bottom) vs. an untreated portion of street.

Application:
CRF is a petroleum-based, oily substance. Once it is sprayed onto the street, the street is covered with a fine limestone aggregate, called “lime screening.” The lime screening prevents cars from tracking the CRF oil. This white substance can create dust when driven over – as experienced this year in Bloomington.

Three test streets running about four blocks total were coated with CRF last year. One dust complaint resulted. This year, CRF was applied to 110 blocks of streets from April 8 to April 17. Complaints were widespread.

 In response to a volume of dust complaints, the City swept the streets. However, the City also discovered that the CRF still had not fully cured.

The dust problem was replaced by a different problem: The tracking of CRF oil as cars passed over CRF-treated streets. In these areas, new lime had to be applied while the CRF continued to cure.

For CRF use in future years, the following steps will be taken, Karch said:

  1. Treated roads will be closed to through traffic until the CRF cures and the remaining lime can be swept off. By keeping through traffic off the streets, far less dust will be generated. “Slow down” signs will be posted to urge motorists to drive slower and, as a result, reduce lime dust. 
  2. Street parking will be banned during the treatment and curing process. Street parking will be eliminated on CRF-treated streets until the CRF cures and the lime screening is swept.
  3. More effort will be undertaken  to notify residents of upcoming CRF work.
  4. City staff will research construction materials in search of a lime screen that will cause less airborne dust.
  5. CRF work may be delayed until the fall in future years. Hotter temperatures slow the curing process.
Jack White, president of Corrective Asphalt Materials, explained the scientific principle behind CRF and Reclamite during a regional conference on pavement preservation in Bloomington in March 2014.  

CRF seminar

 More reading on CRF

From the contractor Jack White from Corrective Asphalt Materials writes about the science behind CRF and asphalt rejuvenators
Asphalt Rejuvenators:
Fact, or Fable?
 A research paper on pavement preservation
From the manufacturer  Tricor Refining brochure on uses for CRF
Bloomington tests  A document on CRF testing in Bloomington