Tar and Chip Gravel Explanation

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Written by Judy

On September 19, 2022

Wondering why there is so much loose gravel on the roads being treated with Tar and Chip?

Office staff have received some questions along these lines, and I understand similar questions/comments have been posted on social media regarding the same.

The approved process for use during tar and chip applications within Lake Holiday is a modified single seal treatment done according to VDOT specification SP314 which states that:

“Approximately 0.17 gallons per square yard of asphalt material (CRS-2L) shall be applied to the existing surface immediately followed by an application of approximately 15 pounds per square yard of aggregate size No. 8P. The aggregate shall be spread uniformly (one aggregate deep) over the treated surface. The aggregate shall be rolled immediately at least once with a self-propelled roller of an approved design. After the seal coat has been rolled a blot seal coat consisting of approximately 0.15 gallons per square yard of asphalt material (CRS-2L) shall be applied to the surface treated pavement followed by a uniform application of approximately 10 pounds per square yard of fine aggregate. The fine aggregate shall be No. 9 aggregate according to Section 203 of the Specifications”

This process results in a large amount of loose stone being applied over top of each spray application of asphalt material (CRS-2L).  This is a normal part of the process and does result in large amounts of loose stone as you see now on the roads being treated.  There will be another spray of .15 gallons per square yard followed by another application of No. 9 stone aggregate in the coming days (the exact timing is dependent upon the contractor’s progress and schedule as they are treating approximately 6 miles while on site). This again will result in loose stone with much of the excess being removed via light mechanical brooming soon thereafter.  It is the normal expectation with this type of treatment that some loose stone will remain for many weeks after the treatment while the material beneath cures and hardens.  Once that has occurred, the roadways may be more heavily broomed mechanically.  It is recommended that this not occur for at least 6 to 8 weeks.

Hopefully this information will help give the reader an understanding of the approved process and why it results in so much loose gravel initially. With approximately 25 pounds of aggregate being applied per square yard during the treatment period, the excess can seem extreme. This amount of stone has been deemed necessary by VDOT to effectively mesh/combine with the applied asphalt liquid when rolled.  Much of this stone does not become a part of the final surface, but it does serve to ensure that stone is adhered to all areas where the asphalt material has been sprayed.

Regards,
Mike

Mike Goodwin
LHCC GM

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